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Monday, December 22, 2008

Christmas Star

This circuit can be used to construct an attractive Christmas Star. When we switch on this circuit, the brightness of lamp L1 gradually increases. When it reaches the maximum brightness level, the brightness starts decreasing gradually. And when it reaches the minimum brightness level, it again increases automatically. This cycle repeats. The increase and decrease of brightness of bulb L1 depends on the charging and discharging of capacitor C3.

When the output of IC1 is high, capacitor C3 starts discharging and consequently the brightness of lamp L1 decreases. IC2 is an opto-isolator whereas IC1 is configured as an astable multivibrator. The frequency of IC1 can be changed by varying the value of resistor R2 or the value of capacitor C1. Remember that when you vary the frequency of IC1, you should also vary the values of resistors R3 and R4 correspondingly for better performance.

The minimum brightness level of lamp L1 can be changed by adjusting potentiometer VR1. If the brightness of the lamp L1 does not reach a reasonable brightness level, or if the lamp seems to remain in maximum brightness level (watch for a minute), increase the in-circuit resistance of potmeter VR1. If in-circuit resistance of potmeter VR1 is too high, the lamp may flicker in its minimum brightness region, or the lamp may remain in ‘off’ state for a long time. In such cases, decrease the resistance of potmeter VR1 till the brightness of lamp L1 smoothly increases and decreases. When supply voltage varies, you have to adjust potmeter VR1 as stated above, for proper performance of the circuit. A triac such as BT136 can be used in place of the SCR in this circuit. Caution: While adjusting potmeter VR1, care should be taken to avoid electrical shock

Thursday, October 30, 2008

Tuesday, October 7, 2008

Bridgeable Amplifiers

Amplifier bridging is simply using 2 channels of an amplifier to drive a common load. For 2 channel amplifiers, one left signal and one right signal is used to drive a mono speaker load. Keep in mind that mono and bridging are not necessarily the same. Mono means that there's only one output signal. There could be more than one speaker but each speaker will have the same output. Bridging means that you are using more than one source of power to drive a load (speaker). The sources of power are one each output from either channel of the amplifier. A long time ago, amplifiers had signal on the positive output speaker terminals only. To bridge one of those amplifiers, you'd have to use some means to invert the signal on one channel (remember the old 'bridging modules' for Orion amplifiers?). Today's bridgeable amplifiers have an inverted channel as part of their design. For many amplifiers, the left positive and right negative are are the signal outputs. A few use the left negative and the right positive. Others still (mostly mono amplifiers that are to be used in bridged pairs) require that you choose 0° or 180° via a switch to invert the signal.

Before we go any farther let me say this... It it NOT necessary to bridge an amplifier to make it produce maximum power. Bridging is simply one option. If an amplifier is 2 ohm stereo stable (and therefore 4 ohm mono stable), it will produce the same power into a 2 ohm stereo load as it will into a 4 ohm mono load. Later, I will explain why this is.

Many people feel that they have to connect every amplifier they own in a 2 ohm mono configuration. These are generally the same people who have owned (and destroyed) many amplifiers. This is because very few amplifiers (especially Class A/B amplifier) are capable of safely driving a 2 ohm mono load. Later, I'll explain why 2 ohms mono is dangerous to most amplifiers.

As was said above, bridging an amplifier simply means using two output terminals both of which have signal on them (there's usually one each from the left and right channels of the amplifier). It is usually done to increase the power output to a speaker or to utilize both channels of a stereo amplifier if you only have one woofer.

To fully understand how amplifiers are bridged, we should first cover "phase" as it applies to audio amplifiers. The following diagram shows 3 sine waves that are out of phase with each other, to varying degrees.

As you can see, the first waveform is the reference. You must have a reference or the term "phase" has no meaning. In the above diagram, the middle waveform is 90 degrees out of phase with respect to both of the other waveforms. The third waveform is 180 degrees out of phase with respect to the reference waveform and 90 degrees out of phase with respect to the middle waveform. The diagram below shows the phase angles in a different type of illustration.

The following diagram shows how the waveform relates to the 360 degrees of a complete circle (one complete cycle of the waveform).
1. The waveform's potential (voltage) is at (equal to) ground (the reference) which, in this case, is the same as "0 degrees". The instantaneous voltage increases as the waveform moves toward 90 degrees.
2. At this point, the waveform has gone through 90 of the 360 degree cycle. This is the point of maximum instantaneous voltage for the sine wave signal. After it passes this point in a counter clockwise direction, the voltage starts to drop. Note that at this point, the speaker would be forced the maximum distance from its point of rest. For most speakers, if this signal were applied to the positive terminal of the speaker and the negative terminal were connected to the reference (ground), the speaker would be pushed out of the box.
3. At point c, the instantaneous voltage is back at reference and we have gone through 180 of the 360 degree total cycle. If another sine wave of the same frequency would start at "A" at this point in time, it would be 180 degrees out of phase with reference to the original waveform. The speaker (mentioned above) would be back at its point of rest at this point in time.
4. This is 270 degrees through the cycle. You can see that the voltage is at it's lowest point (it's actually at its maximum negative instantaneous voltage). At this point in time, the speaker would be pulled in. The voltage will start to increase as it moves through this point. When the waveform reaches point "A", it starts a new cycle.

This diagram shows 2 waveforms and the reference to the 360º cycle.

And this diagram shows two sine waves that are 180º out of phase.

In diagram C, there are 2 sine waves. The first waveform is the "normal" sine wave. The bottom waveform is "inverted" or 180 degrees out of phase with respect to the "normal" signal. In a 2 channel (left and right) bridgeable amplifier, one output is in phase with the input signal and the other channel is inverted. In most bridgeable amplifiers, especially American made amps, the left positive has the in phase signal and the right negative has inverted signal.
In diagram D, you can see that both negative terminals, on the non-bridgeable amp, go to a reference point inside of the amp. This means that there is no signal on those connections. In many amplifiers, the reference is actually 'ground'. You will also see that both positive terminals have a normal (non-inverted) signal on them.

In contrast...

The left channel of the bridgeable amplifier is set up just like the left channel of the non-bridgeable but the right channel of the bridgeable amp is where you will see the difference. Notice that the right negative has the signal on it, also notice that the signal is inverted (flipped upside down).

In the following diagram, you can see a speaker connected in a normal configuration and another speaker connected in bridged mode. You can see that the peak voltage available to the normal speaker is 1/2 the voltage available to the bridged speaker (between points A and B). The normal connection uses 1 signal lead and the reference (ground). The bridged speaker uses 2 signal leads. Since the voltage available to the bridged speaker is doubled (between points C and D), the power driven into the speaker can be four times as much as the normal connection (remember that P=E2/R).
Remember that the AC voltage across a speaker's voice coil is what determines the amount of power dissipated by the voice coil (and ultimately how much sound pressure the speaker will produce). In other words, when more voltage is applied to a speaker, the speaker will play louder. If one speaker terminal is connected to a reference point which has no signal (commonly referred to as ground-indicated by the red line) and the other speaker terminal is connected to the signal (speaker output) lead of the amplifier, you will only be able to get half of the power supply's total voltage across the speaker at any point in time.

Realize that a speaker must move equally in both directions from its point of rest. If the amplifier's power supply output is 40 volts total or ±20 volts with "ground" as the reference, the maximum instantaneous voltage that can be applied across the non-bridged speaker's terminals is 20 volts. Well this would be true if the amplifier components were 100% efficient. In the real world the output voltage would be somewhat lower due to inefficiencies but we won't worry about inefficiency right now. For now assume that the full power supply voltage (positive or negative) can be driven into the speaker. If you remember the section on Ohm's law, you will understand that the amp will only be able to produce 100 watts (peak power) into a 4 ohm speaker.

Power=(voltage across speaker*voltage across speaker)/(resistance of the speaker)
Power=(20*20)/4 ohms
Power=100 watts


1. I used resistance instead of impedance because, for this example, impedance would complicate things greatly.
2. Even with 100% amplifier efficiency, The RMS power would only be 1/2 of the power output indicated. The 100 watts is peak power.

Now, what if you have only a single 4 ohm speaker and a 2 channel NON-bridgeable amplifier with sufficient current output capability to drive a 2 ohm load on each of its output channels? You know that the amplifier could produce MUCH more (and also maximum) power into four 4 ohm speakers (which would be equal to a 2 ohm load per channel), but maximum power would not be produced into the single 4 ohm speaker on a single output channel (i.e. left OR right). To produce maximum power into a single 4 ohm speaker (without increasing the rail voltage) you could simply invert the signal of one channel and bridge the speaker on the amplifier. This is why some of the older amplifiers used a 'bridging module' (it inverted the signal going to one channel). It is very easy to invert one channel when designing an amplifier and it makes the amp much more versatile. When one channel is inverted, it's output voltage is of the same magnitude as the "normal" channel but is of opposite polarity (as indicated by the violet and yellow lines of the following diagram).

At any point in time, if the normal channel's output voltage is positive, the inverted channel's output voltage is negative and vice-versa. The inverted channel is basically a mirror image of the normal channel. Now remember that 4 ohm speaker and the fact that the power dissipated in it's voice coil is determined by the voltage across its terminals. With the bridgeable amp, one of the speaker's terminals would be connected to the normal output channel (violet waveform) and the other speaker terminal would be connected to the inverted channel (yellow waveform) of the amplifier. This allows you to get the total power supply voltage across the speaker. Remember, we are not concerning ourselves with inefficiencies within the amplifier. You can see by the following formula, that the power getting to the speaker is much greater.

Power=(40*40)/4 ohms
Power=400 watts

You can see that this is considerably more power! (100 watts unbridged and 400 watts bridged)

If an amplifier is only rated to drive a 4 ohm minimum load on each of its channels, it WILL fail if you try to drive a 4 ohm bridged mono load. If you have an amplifier rated to drive a 2 ohm stereo load (2 ohms on each channel), it's only going to be able to drive a 4 ohm bridged mono load. A 2 ohm bridged mono load will more than likely destroy the amplifier.

2 Ohm Stereo vs 4 Ohm Mono Loads

There seems to be some confusion as to why a 4 ohm mono and a 2 ohm stereo load are the same, as far as the amplifier is concerned. When two 4 ohm speakers are connected to each channel of a 2 channel amplifier, the amplifier is capable of driving the speakers with half of the total power supply voltage. If the amplifier has a power supply which produces plus or minus 20 volts, it will not be able to drive the speakers on a single channel with any more than 20 volts at any point in time. If we have a 2 ohm load on each channel, at the highest point on the waveform the amplifier will apply 20 volts to the speaker load. Remember that we are only considering a single point in time for this example. If we go back to ohms law...

I=10 amperes

If we take a single 4 ohm speaker and bridge it on that same amplifier, the amplifier will be able to apply twice the voltage across the speaker. This is because while one speaker terminal is being driven positive (towards the positive rail), the other terminal is being driven towards the negative rail. This will allow the entire power supply voltage to be applied to the speaker's voice coil. It will now be able to drive the 4 ohm speaker with 40 volts instead of 20 volts in the previous example. Back to Ohm's law...

I=10 amperes

The same amount of current flows through the output transistors whether the amplifier is driving a 4 ohm mono load or 2 ohm stereo load. As far as the amplifier is concerned, they are the same load.

Some people say that when an amplifier is bridged onto a 4 ohm load, it 'sees' a 2 ohm load. While it is true that the same current flows whether the amp is bridged on a 4 ohm load or a 2 ohm stereo load, the amplifier is driving a 4 ohm load across its outputs. A single 4 ohm speaker can never be a 2 ohm load.

Why a 2 Ohm Mono Load May Damage Your Amplifier

As you saw in the previous discussion, a 4 ohm mono load is the same as a 2 ohm stereo load as far as the amplifier is concerned. Looking at the diagram below, configuration 'x' shows a 2 ohm stereo load. Configuration 'y' shows a 4 ohm mono load. If both amplifiers are driven to the same output level, the current flowing through the outputs would be equal. In configuration z we have added another 4 ohm speaker bridged onto the amplifier. This means that the load has doubled which means that there is only one half of the impedance of configuration 'y'. Remember that impedance is the opposition to the flow of electrical current. An amplifier depends on a high enough impedance to prevent too much current flow through the output transistors. When the load is lowered to 2 ohms mono as in configuration z, the current flow through the output transistors is doubled (4 ohms mono vs 2 ohms mono). The amplifier's maximum safe output current may be only slightly higher than that needed to drive a 4 ohm mono or 2 ohm stereo load. When the amplifier tries to drive the 2 ohm mono at full rail voltage (40 volts) the safe operating area of the transistors will (more than likely) be exceeded. Keep in mind that we are talking about the most common types of amplifiers which are designed to drive 2 ohms or higher per channel (2 ohm stereo stable and 4 ohm mono stable amplifiers). There are amplifiers (high current amplifiers) which are designed to drive low impedance loads. These amplifiers have more transistors and heavier duty components to withstand the increased flow of current through the output transistors.
You should remember:
1.When a speaker is bridged onto an amplifier, BOTH speaker terminals are driven with a signal.
2.The signal on one speaker terminal is a 'normal' signal while the signal on the other speaker terminal is 'inverted'

Monday, September 29, 2008

Atmel ISP Programmer

It connects to the Parallel port, and can be used to program any Atmel AVR while it is still in the system, provided the system provides a standard In System Programming (ISP) connector. The PC interface is through the Parallel port, and makes use of the same pinout as the STK-200 programmer from Kanada Systems. The STK-200 programming cable is very popular, and almost every ISP download software (Except ICCAVR's inbuilt chip programmer) supports it.


The device is very simple, it only contains a single chip, a 74LS245 (a 74LS244 can also be used, with suitable modifications). Of course, a 74HC245 can be substituted. I think this is necessary when programming the ATMega series devices with the Atmel AVRISP software, since it uses some sort of 'fast-mode' that gives an error during programming. Ignoring the error doesnt seem to do harm, and the program executes correctly on the chip. Other programmers such as PonyProg( not have any problems, regardless of the device being programmed.

The standard ISP pinouts

The standard pinouts are as shown above. The pins are:
AVR-ISP pinouts
RESETUsed to reset the target system under the PC's control.
SCKThe serial data clock
MOSIMaster Out Slave In, used to send data from the PC (master) to the AVR (slave). Data is transmitted on the edges of SCK.
MISOMaster In Slave Out, used to send data from the AVR (master) to the PC (slave). Data is transmitted on the edges of SCK.
LEDThe PC makes this line high to indicate that programming is occuring. Not used in all systems.
PWRCan be used either to provide power to the target system during programming, or for the programmer to draw power from the target system during programming. I use it to allow the programmer to draw power from the system.

The circuit

The only chip used in the device is a 74LS245 octal bidirectional 3-state driver. However, a 74LS244 octal unidirecional bus driver may also be used. I just happened to have a 74LS245 lying around. The chip is used so that when the device is not being programmed, the programming interface lines are all tristated, allowing the device to function normally. The direction control is permanently grounded, making the device essentially unidirectional. The tristate enable is connected to one of the outputs of the parallel port, along with a pullup. Hence, when the programmer is not plugged into a port, or when the device is not being programmed, the '245's outputs go into tristate mode. Notice that pins 2 and 12, along with pins 3 and 11 are connected together. This is the identification method used by programmer software to determine that an STK-200 compatible programmer is attached to the parallel port. I havent used the programming LED option, and chose not to use a power-on LED, so that the device being programmed has the least load on it's power supply.
The whole device was assembled on a veroboard, nothing special. It works fine and gives no problems, except when programming an ATMega103 using AVRISP.


Software compatible with this programmer includes
  • AVR ISP from Atmel(, a very good device programmer. It can read/write the Flash and EEPROM, and set the security bits. It includes a nice "Autoprogram" command, that reloads all the device files and downloads the ones that have changed to the AVR.
  • PonyProg, by Claudio (, another nice programmer, a bit slower than AVRISP. However, it can be used to program lots of other types of devices, such as EPROMS, serial EEPROMS, etc.
  • CodeVisionAVR C compiler's inbuilt chip programmer, by HP Infotech ( , has the advantage of being a part of the compiler IDE.


Here introduce the temperature regulator(Thermostat) which used a thermistor for the temperature sensor. This circuit can control a outside system by driving a relay when the temperature of the thermistor becomes a setting temperature. The strict temperature setting can not be done with this circuit like the thermometer. The resistance value of the thermistor changes by the ambient temperature. This circuit changes the change of the resistance value into the change of the voltage using the transistor. Then, it compares that voltage and the voltage of the setting temperature using the voltage comparator and it drives a relay. It is a relatively simple circuit. With this circuit, the difficult point is to handle an analog signal (the temperature change). The characteristic of the thermistor, the transistor and so on has an influence on the performance of the equipment just as it is. Even if the thermistor or the transistor of the same name is used, the same performance (the setting temperature range and so on) isn't sometimes gotten. The design to have considered the ruggedness of the part is possible. This time, I made a circuit based on the result which measured the characteristic of each part. I think that this way becomes reference as the case when there is not data of the part.

Heat Sensitive Switch

At the heart of this heat-sensitive switch is IC LM35 (IC1),which is a linear temperature sensor and linear temperature-to-voltage converter circuit. The converter provides accurately linear and directly proportional output signal in millivolts over the temperature range of 0°C to 155°C. It develops an output voltage of 10 mV per degree centigrade change in the ambient temperature. Therefore the output voltage varies from 0 mV at 0°C to 1V at 100°C and any voltage measurement circuit connected across the output pins can read the temperature directly.

The input and ground pins of this heat-to-voltage converter IC are connected across the regulated power supply rails and decoupled by R1 and C1. Its temperature-tracking output is applied to the non-inverting input (pin 3) of the comparator built around IC2. The inverting input (pin 2) of IC2 is connected across the positive supply rails via a voltage divider network formed by potmeter VR1. Since the wiper of potmeter VR1 is connected to the inverting input of IC2, the voltage presented to this pin is linearly variable. This voltage is used as the reference level for the comparator against the output supplied by IC1. So if the non-inverting input of IC2 receives a voltage lower than the set level, its output goes low (approximately 650 mV). This low level is applied to the input of the load-relay driver comprising npn transistors T1 and T2. The low level presented at the base of transistor T1 keeps it nonconductive. Since T2 receives the forward bias voltage via the emitter of T1, it is also kept non-conductive. Hence, relay RL1 is in de-energised state, keeping mains supply to the load ‘off’ as long as the temperature at the sensor is low.

Conversely, if the non-inverting input receives a voltage higher than the set level, its output goes high (approximately 2200 mV) and the load is turned ‘on.’ This happens when IC1 is at a higher temperature and its output voltage is also higher than the set level at the inverting input of IC2. So the load is turned on as soon as the ambient temperature rises above the set level. Capacitor C3 at this pin helps iron out any ripple that passes through the positive supply rail to avoid errors in the circuit operation. By adjusting potmeter VR1 and thereby varying the reference voltage level at the inverting input pin of IC1, the temperature threshold at which energisation of the relay is required can be set. As this setting is linear, the knob of potmeter VR1 can be provided with a linear dial caliberated in degrees centigrade.

Therefore any temperature level can be selected and constantly monitored for external act ions like turning on a room heater in winter or a room cooler in summer. The circuit can also be used to activate emergency fire extinguishers, if positioned at the probable fire accident site. The circuit can be modified to operate any electrical appliance. In that case, relay RL1 must be a heavy-duty type with appropriately rated contacts to match the power demands of the load to be operated

300W 6x LM3886 bridged-paralleled power amplifier

Power Amplifier 150W(single channel)

Unbalanced to Balanced Line Converter

This circuit will convert unbalanced audio lines to balanced audio lines. Here's the schematic diagram using NE5532 dual opamp chips, some resistors and capacitors.

We all know that balanced lines have less susceptibility to noise, especially on long distances. This is common knowledge.But I'd like to point out one more benefit of balanced signals that I just realized this afternoon. And that benefit is you'll have 6db more gain in a balanced signal compared with the original unbalanced signal!!! Mathematically, we know it would happen, but seeing it as a real waveform in Sonar is proof of concept.

What's the big deal about 6db gain?
6db of gain is DOUBLE the signal strength... which means, your signal is going to be hotter, without any changes in your setup. Thus, you don't have to increase your preamp/mixer's gain as much to achieve a good loud level, and since the signal increased by 6db, it also goes into saying that you just reduced your noise by 6db too, i.e. you also reduced noise by half.

You see, MOST gear are really unbalanced inside. They just have balanced drivers at the output stage. And some mastering engineers (read Bob Katz's book) prefer unbalanced gear ( yeah, I was shocked to hear this). His reasoning that since all the gear are plugged in one room anyway, and the inside circuitry of gear are almost always unbalanced, and depending on how the balanced circuit driver was made, could degrade the signal, etc... This guy knows electronics and his statement actually makes sense.

But he also said that there are some truly balanced circuitry where you can't take away any part out, and these are almost always the best kind of gear.

Back to the topic... the circuit above can be added to any unbalanced out and make it balanced. The 2 driver opamps drive each half of the signal, one being 180-degree inverted. In this case, the rejection of EMI and RFI is between the lines of the balanced input and output gears.... not within the gear itself. If you can isolate the unbalanced-to-balanced driver circuit in a device and the device can still work, then that device is really unbalanced.

From the input transformer, all the way to the output transformer, it is balanced. i.e. I can't take away the output transformer and still have this functioning right. I can't take away the input transformer and still have it functioning. The input and output transformer makes this gear have balanced inputs and outputs, and the supporting circuitry inside relies on connecting to these transformers to do its job.

The above circuit is an ACTIVE balanced driver. i.e. it requires power.

Wednesday, August 6, 2008

LA4440 - 6W 2-Channel, Bridge 19W

LA4440 - 6W 2-Channel, Bridge 19W typ Audio Power Amplifier

Manufacturer: SANYO


  • Built-in 2 channels (dual) enabling use in stereo and bridge amplifier applications.
  • Dual : 6W´2 (typ.)Bridge : 19W (typ.)
  • Minimun number of external parts required.
  • Small pop noise at the time of power supply ON/OFF and good starting balance.
  • Good ripple rejection : 46dB (typ.)
  • Good channel separation.
  • Small residual noise (Rg=0).
  • Low distortion over a wide range from low frequencies to high frequencies.
  • Easy to design radiator fin.
  • Built-in audio muting function.
  • Built-in protectors.

  • a. Thermal protector
    b. Overvoltage, surge voltage protector
    c. Pin-to-pin short protector

    Pin No. Pin Name
    1 NF1
    2 IN 1
    3 Preamp. GND
    4 Audio Muting
    5 DC
    6 IN2
    7 NF2
    8 Power AMP GND2
    9 B.S2
    10 OUT2
    11 Vcc
    12 OUT1
    13 B.S1
    14 Power AMP GND1

Tuesday, August 5, 2008

FM Wireless Mike

FM Wireless Mike can transmit voice signals to any FM Radio receiver 100 meters away. The circuit is basically a frequency modulated transmitter working at 100 MHz. The frequency of the transmitter can be varied slightly by changing the trimmer C5. You can use ordinary condenser mike in this circuit. The transistors can be replaced by any low power transistors like BC148 or BF494.

The coil L1 is air core 6 turn 24 SWG. Third turn is tapped and connected to telescopic antenna. You can replace telescopic antenna with a small piece of wire.

Miniature MW Transmitter

Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speeches or songs within a short range.

The circuit uses only one transistor. The entire circuit can be easily assembled on a prototyping printed circuit board. After assembling all the components properly put the whole assembly in a plastic enclosure provided with a telescopic antenna. Now keep your MW radio and the transmitter on a table about one meter away from each other. Switch on the radio receiver and turn to a clear spot where no broadcasting station is present. Now switch on the transmitter and turn the gang condenser. At some position loud hissing sound will be heard from your receiver. Stop the gang condenser at this position. Speak some thing to the speaker which serves as the microphone. Now turn the radio receiver to get clear and loud sound.

The transmitter have a range of 200 meters. You can increase the range by using an external antenna and sensitive receiver at receiving end.

600 Volt Power Supply For QRO

Amateur Radio Transmitters using valves such as 807 or1625 works well with a plate voltage between 600V to 700 Volts.The circuit described here is a full wave voltage doubler. The output voltage is twice the input voltage. For 230V AC input the output will be nearly 600 Volts.

Resister R1 is used to limit the initial high voltage and high currents. Capacitor C1, C2, C3 together with coils L1 and L2 form input line filter. The capacitors C4 and C5 protects diodes from high voltage transients on the AC line as well as reduces inter carrier hum modulation of the R.F picked up by the mains. Capacitors C6 and C7 provides enough filtering for the output DC Voltage.

C1, C2, C3 - 0.1 mf 630V
C4, C5 - 0.01 mf 630V
C6, C7 - 100 mf 450V
R1 - 10E 5W Wire Wound
R2, R3 - 220KE 2Watts
D1, D2 - BY127
D3, D4 - BY127
L1, L2 - 12 Turns 18 SWG
Wound over 4 Cm
long Ferrite Rode.

Ceramic Filter Beat Frequency Oscillator

BFO is a simple device which helps us to listen SSB and CW transmissions. Reception of SSB and CW signals requires a product detector or BFO (Beat Frequency Oscillator) to reinsert the missing carrier. This circuit is very simple since it requires no turned circuit and hence no adjustment in the BFO circuit. The number of components required is also very limited. To produce 455 Khz carrier a ceramic filter is used. It cost me Rs: 6/- only. The RF choke (RFC) is made by winding 150 turns of enamelled wire on half watt 150 K carbon resistor.

When receiving Single Side Band (SSB) signals the locally generated carrier beats with the SSB signal to produce the complete audio signal. Because the ceramic filter operates at fixed frequency, no turning is required to demodulate the single side band (SSB) signals and no regulated power supply is necessary. First tune your AM radio to some SSB signal and switch on the BFO and slightly adjust receiver turning for good resolved audio quality. To resolve stronger stations connect a wire not bigger than 10 cm to the out put of the beat frequency oscillator.

Most of the BC receivers use 455 KHz as IF amplifier frequency. Some receivers have an IF Frequency which lies between 450 and 460 KHz. For best result the receiver IF amplifier frequency and the beat frequency oscillator frequency should be the same.


They will be swarming once again, the unwanted, winged torturers, looking for the victims and leaving behind swelling and itch!

The mosquito problem is a part of everyday life, espacially during the summer.

Since the immemorial, inventive people have struggled hard to find effective means of protection against these insects. Even though it is a fact that only the females are dangerous, the males can also create situations of panic by their humming. Scientists say that these and many other insects find some particular frequencies of sound very unpleasent abd run away from these frequencies.

It seems quite obvious then, that by creating these insects frequencies electronically, we should be able to repel these insects! The most important point to remember here is that, unfortunately, this method has so far not been completely sucessfull. Whereas one group of insects can be made to run away at frequencies around 5 KHz, other types may desert only at higher frequencies, about 10 to 20 KHz. For some types, all the frequencies may fall on deaf ears! Yet other theories propose that in fact some frequencies may even attract them instead of repelling.

Whatever may be the truth, trial is superior to just theorising. Even though the cost of our circuit may prove to be a wrong investment, as the population of mosquitoes and insects who are immune to our insects/mosquito repellant is likely to be predominant ! The loss is very high - four resistors, two capacitors, two transistors and a buzzer.


The Astable Multivibrator, which is generally used as a signal generator, is once again used here to generate the desired frequencies. It is an excellent example of the fact, how versatile simple basic electronic circuit can be.

Let us quicklt see the operation of the astable multivibrator circuit. When T1 is conducting T2 is off and when T2 is conducting, T1 is off. The capacitors C1 and C2 contributes decisively to this ON/OFF cycles for the transistors T1 and T2. The time taken by C1 and C2 to charge and discharge decides the shape of the output waveform. Another important factor in the operation of the circuit is the fact that the transistor goes into conduction only when the base-emitter voltage exceeds 0.7 volts (for silicon transistors). From this basic knowledge we can visualise how the transistors exchange their roles and how the voltage on the collector of each transistor jumbs between the lower and upper level, producing a rectangular waveform. If you take a close look at circuit, you will notice that C1 and C2 are not equal. They differ in their values by afactor of four.

The output signal will thus be a non symmetrical waveform. Such a non symmetrical signal contains more high frequency harminics compered to the normal square wave signal. The output of our circuit will have the basic frequency of 5 KHz along with harminics of 10, 15 and 20 KHz. If some insects are deaf to frequencies upto 5 KHz, they may react to 10 KHz or 15 KHz or even 20 KHz, one never knows ...

The piezo buzzer used should not have an internal oscillator built into it. The circuit consumes 0.3 ma current, and can give about 1500 hours of nonstop operation.

R1,R4 - 10 K Ohm
R2,R3 - 560 K Ohm
C1 - 82 PF
C2 - 330 PF
T1,T2 - BC547
Piezo Buzzer (Without internal oscillator)

Thursday, July 31, 2008

Active Sub Whoofer

Variable Regulated Powersupply(1.2 to 30V @ 1.5 Amps)

Parts List
BR1 = Bridge Rectifier, 100V - 3A
C1 = 2200 ìF, 63V
IC1 = LM317, adjustable regulator
C2 = 0.1 ìF
V = Meter, 30V,
Ri = 85 ohm
C3 = 1 ìF, 40V
TR1 = Transformer, 25V, 2A Plug = 3-wire plug & cord
R1 = 1K8, 5%
S1 = On-Off toggle switch
R2 = 220 ohm, 5%
D1 = 1N4001
R3 = 27K, 5%
Fuse = 110V, 500mA, slow-blow
P1 = 5K, potentiometer FuseHolder, wire, solder, case, knob for P1
P2 = 10K, 10-turn trim-pot Red & Black Banana Jacks

Couple Notes:

This is a simple, but low-ripple powersupply, and an excellent project if you're starting out in electronics. It will suit your needs for most of your bench testing and prototypeapplications. The output is adjustable from 1.2 volts to about 30 volts. Maximum current is about 1.5 amps which is also sufficient for most of your tinkering. It is relatively easy to build and can be pretty cheap if you have some or all the required parts. A printed circuit board is not included and I'm not planning on adding one since the whole thing can easily be build on perforated or vero board. Or buy one of Radio Shack/Tandy's experimenters boards (#276-150). Suit yourself. The meter and thetransformer are the money suckers, but if you can scrounge them up from somewhere it will reduce the cost significantly. BR1 is a full-wave bridge rectifier. The two '~' denotes 'AC' and are connected to the 25vac output coming from the transformer. IC1 is a 3-pin, TO-220 model. Be sure to put a cooling rib on IC1, at it's max 1.5 A current it quickly becomes very hot...
Most of the parts can be obtained from your local Radio Shack or Tandy store. The physical size of the power supply case depends largely on the size of the meter &: transformer. But almost anything will do, even wood. Go wild.

Circuit Description:
The 110V-AC coming from the powercord is fed to the transformer TR1 via the on-off switch and the 500mA fuse. The 30vac output (approximately) from the transformer is presented to the BR1, the bridge-rectifier, and here rectified from AC (Alternating Current) to DC (Direct Current). If you don't want to spend the money for a Bridge Rectifier, you can easily use four general purpose 1N4004 diodes. The pulsating DC output is filtered via the 2200ìF capacitor (to make itmore manageable for the regulator) and fed to 'IN'-put of the adjustable LM317 regulator (IC1). The output of this regulator is your adjustable voltage of 1.2 to 30 volts varied via the 'Adj' pin and the 5K potmeter P1. The large value ofC1 makes for a good, low ripple output voltage.
Why exactly 1.2V and not 0-volt? Very basic, the job of the regulator is two-fold; first, it compares the output voltage toan internal reference and controls the output voltage so that it remains constant, and second, it provides a method for adjusting the output voltage to the level you want by using a potentiometers. Internally the regulator uses a zener diode to provide a fixed reference voltage of 1.2 volt across the external resistor R2. (This resistor is usually around 240 ohms, but220 ohms will work fine without any problems). Because of this the voltage at the output can never decrease below 1.2volts, but as the potentiometer (P1) increases in resistance the voltage across it, due to current from the regulator plus current from R2, its voltage increases. This increases the output voltage.
D1 is a general purpose 1N4001 diode, used as a feedback blocker. It steers any current that might be coming from the device under power around the regulator to prevent the regulator from being damaged. Such reverse currents usually occur when devices are powered down.The 'ON' Led will be lit via the 18K resistor R1. The current through the led will be between 12 - 20mA @ 2V depending on the type and color Led you are using. C2 is a 0.1ìF (100nF) decoupler capacitor to filter out the transient noise which can be induced into the supply by stray magnetic fields. Under normal conditions this capacitor is only required if the regulator is far away from the filter cap, but I added it anyway. C3 improves transient response. This means that while the
regulator may perform perfectly at DC and at low frequencies, (regulating the voltage regardless of the load current), at higher frequencies it may be less effective. Adding this 1 ìF capacitor should improve the response at those frequencies.
R3 and the trimmer pot (P2) allows you to 'zero' your meter to a set voltage. The meter is a 30Volt type with an internal resistance of 85 ohms. I you have or obtained a meter with a different Ri (internal resistance) you will have to adjust R3 to keep the current of meter to 1mA. Just another note in regards this meter, use the reading as a guideline. The reading may or may not be off by about 0.75volts at full scale, meaning if your meter indicates 30 volts it may be in reality almost 31volts or 29 volts. If you need a more precise voltage, then use your multimeter.

Because of the few components you can use a small case but use whatever you have available.I used a power cord from a computer and cut the computer end off. All computer power cords are three-prong. The ground wire, which is connected to the middle pin of the power plug is connected to the chassis. The color of the ground-wire is either green or green/yellow. It is there for your protection if the 110vac accidentally comes in contact with the supply housing (case). BE CAREFUL always to disconnect the powerplug when you working inside the chassis. If you choose to use an in-line, or clip-type fuseholder be sure to isolate it with heat shrink or something to minimize accidental touching.
I use perf-board (or Vero board) as a circuit board. This stuff is widely available and comes relatively cheap. It is either made of some sort of fiber material or Phenolic or Bakelite pcb. They all work great. Some Phenolic boards come with copper tracks already on them which will make soldering the project together easier. I mounted the LM317(T) regulator on a heatsink. If you use a metal/aluminum case you can mount it right to the metal case, insulated with the mica insulator and the nylon washer around the mounting screw. Note that the metal tab of theLM317 is connected internally to the 'Output' pin. So it has to be insulated when mounting directly to the case. Use heat sink compound (comes in transparent or white color) on the metal tab and mica insulator to maximize proper heat transfer between LM317 and case/ or heatsink.
Drill the holes for the banana jacks, on/off switch, and LED and make the cut-out for the meter. It is best to mount everything in such a way that you are able to trouble-shoot your circuit board with ease if needed. One more note about the on-off switch S1, this switch has 110VAC power to it. After soldering, insulate the bare spots with a bit of silicon gel. Works great and prevents electrical shock through accidental touching.
If all is well, and you are finished assembling and soldering everything, check all connections. Check capacitors C1 & C3 for proper polarity (especially for C1, polarity reversal may cause explosion). Hookup a multimeter to the power supply output jacks. Set the meter for DC volts. Switch on S1 (led will light, no smoke or sparks?) and watch the meter movement. Adjust the potentiometer until it reads on your multimeter 15Volts. Adjust trimpot P2 until the meter also reads 15volts. When done, note any discrepancies between your multimeter and the power supply meter at full scale (max output). Maybe there is none, maybe there is a little, but you will be aware of it. Good luck and have fun building!

Final Note:
You can add two silicon diodes (in series) to the output of the LM317 to drop the final 1.2V, giving the full 0-30V range. I built a similar supply using the LM317, to supply a wafer coating spinner motor. The 1.2V kept the motor spinning at over100rpm, which was unacceptable to the researcher, who needed to ramp the motor speed from 0-8krpm.

Active Antenna for AM/FM/SW

This simple little circuit can be used for AM, FM, and Shortwave(SW). On the shortwave band this active antenna is comparable to a 20 to 30foot wire antenna. It is further more designed to be used on receivers that use untuned wire antennas, such as inexpensive units and car radios.

L1 can be selected for the application. A 470μH coil works on lower frequencies and lie in AM, for shortwave try a 20μH coil. This unit can be powered by a 9 volt alkaline battery. If a power supply is used, bypass the power supply with a 0.04μF capacitor to prevent noise pickup. The antenna used on this circuit is a standard 18-inch telescoping type, but a thick piece of copper, bus-bar, or piano wire will also work fine.
The heart of this circuit is Q1, a JFET-N-Channel, UHF/VHF amplifier in a TO-92 case.It can be replaced with an NTE451.Output is taken from jack J1 and run to the input on the receiver.

FM Radio Antenna Amplifier

Active FM-Amplifier:

With only a small handful of parts you can built this trusty FM Amplifier. It works with only 1 UHF/VHF type transistor, MFE201. This amplifier will pull in all distant FM stations clearly. The circuit is configured as a common-emitter tuned RF pre-amplifier wired around VHF/UHF transistor MFE201. There are a couple other models that probably would work too, like the NTE107, 2SC2570, etc. but I have not tried it.

Adjust capacitor trimmers C1 and C2 for maximum gain. Input coil L1 consists of 4 turns of 20SWG enameled copper wire over a 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has onlythree turns. Pin configuration is shown in the diagram.

Wednesday, July 9, 2008

AM DSB Transmitter for HAMS

This circuit of AM transmitter is designed to transmit AM(amplitude modulated) DSB (double side Band) signals. A modulated AM signal consists of a carrier and two symmetrically spaced side bands. The two side bands have the same amplitude and the carry same information. In fact, the carrier itself conveys or carries no information. In a 100% modulated AM signal 2/3rd of the power is wasted in the carrier and only 1/6th of the power in each side band
In this transmitter we remove the carrier and transmits only the two side bands. The effective output of the circuit is three times that of an equivalent AM transmitter.

Opamp IC741 is added here as a microphone amplifier to amplify the audio signals from the condenser mike. The output of the Opamp is fed to the double balanced modulator build around In4148 diodes. The modulation level can be adjusted with the help of preset VR1.
The carrier using cristal wired around BC548 transistor T2. The carrier is further amplified bt transistor T1, which also acts as a buffer between modulator. The working frequencey of the transmitter can be changed by using the cristals of the diffreent frequencies. For multi-frequency operation, selection of different cristals can be made using a selector switch. The level of the carrier coupled to the DEM(double Balanced Modulator) cna be adjusted with the help of preset VR2.

The output of the DBM contains only the product (of audio and carrier) frequencise. The DBM supress both the input signals anf produce the double side band supressed carrier(DSBSC) at its output. However, since the diodes used in the balanced modulator are not fully matched , the output of the DBM does contain some residual carrier. This is known as carrier leckage. By adjusting the 100-ohm preset(VR2) and the trimmer (c7) you can nullify the carrier leckage.

To receive DSb signals you need a Beat Frequency Oscillator(BFO) to reinsert the missing carrier. If you dodn't have a BFO, or want to transmit only AM signal, adjust preset VR2 to leak some carrier so thar you can receive the signals on any ordinary radio receiver. In AM mode 100% modulation can be attained by adjusting presets VR1 and VR2.
The DSBSC signal available at the output of the balanced modulator is amplified by two stages of RF libnear amplifiers. Transisor 2n2222A(t3) is used as an RF amplifier., which provides enough signal amplification to drive the final power amplifier around transistor SL100B. The output of the final power amplifier is connected to the antienna.

All coils are to be wound on ferrite balun cores(same ast used in TV balun transformer of size 1.4cm x 0.6 cm) using 24 SWG enameled copper wire. proper heat-sink should be provided for SL100B transistor used as final power amplifier.

Range of the order of a few kilometers can be easily achieved by proper choice of the site, type of antenna (such as a resonant half-wave dipole of lenght 10 meters for 7.08 Mhz frequency) and proper matching of transmitter to the antanna. Use good quality shielded wire of short length to connect the crystals.

Saturday, June 7, 2008

60W Linear amplifier

The 60 Watt linear amplifier is simple all solid state circuit using power mosfet IRF840. The IRF series of power transistors are available in various voltage and power ratings. A single IRF840 can handle maximum power output of 125 watts. Since these transistors are used in inverters and smps they are easily available for around Rs: 20/-.

The IRF linear amplifier can be connected to the out put of popular VWN-QRP to get an output of 60 Watts. The circuit draws 700 ma at 60 Volt Vcc. Good heat sink is a must for the power transistor.

Alignment of the circuit is very easy. Connect a dummy load to the out put of the circuit. You can use some small bulb like 24V 6Watts as the dummy load. I have even used 230V 60Watts bulb as dummy load with my IRF840 power amplifier working at 120Volts. Adjust the 10K preset to get around 100 ma Drain current. I used gate voltage of 0.8V with my linear amplifier. A heigh gate voltage can make the power transistor get distroyed by self oscillation. So gate voltage must be below 2V and fixing at 1V will be safe.

Bifalar transformaer T1 is wound with 8 turns 26SWG on 1.4 x 1 balun core.
The coil on the drain of IRF is 3 turns 20 SWG wound on 4 number of T13.9 torroids (two torroids are stacked to form a balun core). The RFC at the Vcc line is 20 Turns 20 SWG wound on T20 torroid.

Saturday, May 24, 2008

555 DC-AC Inverter

Parts List:
R1 = 10K
R2 = 100K
R3 = 100 ohm
R4 = 50K potmeter, Linear
C1,C2 = 0.1uF
C3 = 0.01uF
C4 = 2700uF
Q1 = TIP41A, NPN, or equivalent
Q2 = TIP42A, PNP, or equivalent
L1 = 1uH
T1 = Filament transformer, your choice

This DC-to-AC inverter schematic produces an AC output at line frequency and voltage. The 555 is configured as a low-frequency oscillator, tunable over the frequency range of 50 to 60 Hz by Frequency potentiometer R4.
The 555 feeds its output (amplified by Q1 and Q2) to the input of transformer T1, a reverse-connected filament transformer with the necessary step-up turns ratio. Capacitor C4 and coil L1 filter the input to T1, assuring that it is effectively a sine wave. Adjust the value of T1 to your voltage.

The output (in watts) is up to you by selecting different components.

Input voltage is anywhere from +5V to +15Volt DC, adjust the 2700uF cap's working voltage accordingly. Replacement types for Q1 are: TIP41B, TIP41C, NTE196, ECG196, etc. Replacement types for Q2 are: TIP42B, TIP42C, NTE197, ECG197, etc. Don't be afraid to use another type of similar specs, it's only a transistor... ;-)

TDA2030 typical application circuit

Friday, May 23, 2008

TDA2030 amplifier circuit to a single power law

Rated at 14 W. Power supply ± 6 ~ ± 18V. Output current, harmonic distortion and pay the small distortion (± 14V / 4 ohm, THD = 0.5%).

TDA2030 amplifier circuit to double the power law

Rated at 14 W. Power supply ± 6 ~ ± 18V. Output current, harmonic distortion and pay the small distortion (± 14V / 4 ohm, THD = 0.5%).

Ta7378P FM wireless microphone circuit

TA7378P using FM radio integrated block the production of FM wireless microphone, external components small, simple and easy system, work stability, particularly suitable for the production of radio enthusiasts. Figure FM wireless microphone for the specific circuit, ICl (TA7378P) includes RF amplifiers, mixers, to enlarge the buffer, the local oscillator circuit and bias, the regulator circuit.
The circuit Qiaomiaodejiang combination of internal circuits, use of the circuit-and AFC (automatic frequency control) the use of a variable capacitor oscillator circuit to generate FM (FM) waves.
In order to reduce the impact of external, in the oscillation between the mixer and a buffer amplifier has. Finally, RF amplifiers zoom through launch FM radio antenna.

99.6MHZ J-power FM transmitter antenna

99.6MHZ J-Power FM transmitter antenna

99.6MHZ J-power FM transmitter antenna 99.6MHZ J-power FM transmitter antenna

10 mm diameter brass refrigeration production with a total length of 3.5 M 10 mm diameter brass refrigeration production with a total length of 3.5 M

15 W transmitter power amplifier 88-108MHZ

The power amplifier can be reactive 1-2 W ,88-108MHZ power FM transmitter As for the expansion of 10-15 W, a single C Larger and multi-level low pass filter components, has a high conversion efficiency and strong Yi-wave suppression.
Circuit see attached map shows, using high-power launch of C1972, its parameters are as follows: 175 MHZ, 4A, 25W, power gain ≥ 8.5 db, as shown by parameters, circuit work center frequency of about 98 MHZ, the importation of about 2 W of RF power , The rated output up to 15 W.
To maintain 88 ~ 108 MHZ with any frequency output reached rating, according to the level before the center frequency of some components to make suitable adjustments. May, when necessary, to reduce low-ball-series, to increase power output. The expansion of the power signals from three low-pass filter Yi-filtered high element of the transmitting antenna feed.
Components choice: In addition to electrolytic capacitor, the other tiles with high-frequency capacitors, C11, C12, C14 use high-frequency characteristics of a good, stable performance of adjustable capacitors, inductors Choke RFC1, RFC2 finished with inductors, must pay attention to the current RFC2 Carrying capacity, should use the coarse diameter Cores with the inductors.
L1-L6 available ø0.8mm the high-intensity enameled wire system, a diameter of about 5 MM, a few laps in the plans to "T" for the units indicated. Q1 ordinary Q9 socket, and supporting the use of plugs. Q2 used for 50 Ω RF output connectors, and then of resistance is smaller, more conducive to impedance matching.
Larger effective power more common for the launch of the C1972, of course, especially if you sufficient money to buy blocks C2538 contour of the gain, power will be even greater.

Debug circuit, be sure to pay attention, the power circuit, we must connect false load (I use 30 1 W, 1500 Ω high-precision metal film resistors made parallel), and there must be enough in the cooling devices, normal working hours Power Of not less than 2.5 A, the antenna impedance strictly equivalent to 50 Ω, can not be used Duanbang drawbars antenna, or a strong current of RF feedback circuit will create their own interference, most of RF energy to space and can not be convergence in the consumption of power, to overheating Damage must be launched for 50 Ω coax, tabled Reply to launch outdoor antenna.
Circuit the normal work of the key lies in whether the circuit debugging, the whole process had to very carefully.
Debugging, enter only the smaller the incentive power supply voltage drop to 9 V, using high-frequency voltage (can not use ordinary multimeter) monitoring false load at both ends of high-frequency voltage value, regulating C12, C14, L3, L4, L5, L6 So that the voltage range of 15-20 V around, and then adjust C11, L1 voltage to the largest.
And then gradually raise the voltage, each raising a voltage repeatedly adjusted C12, C14 and C11, L1 so that the maximum output voltage, noted that the input voltage and RF power simultaneously increasing incentives to ensure the accuracy of the results of debugging. Reach rating, 13.8 V supply voltage of about 2 A current work around, 50 Ω-load resistance at both ends voltage ≥ 40 V, RF power output of 15 W.

With the RF power amplifier with 50 Ω-wide umbrella to the vertical launch antenna (gain of about 2 dB), to ordinary FM radio test fired from the coverage of not less than 15 KM

VHF UHF TV modulator

Simple TV Modulator that working on VHF UHF Band, the oscillator generates frequency is modulated with the video signal and the modulated carrier wave thus generated is fed into the TV set's aerial input via a cable. Then all that remains to do is tune the VHF UHF TV set to the correct frequency.
The harmonics generator converts the oscillator signal into a sort of frequency spectrum containing all the multiples of 27 MHz up to about 1800 MHz. The TV modulator's output signal is made up of a large number of little peaks, each of which is a complete transmitter signal. At least one of these will always be in band I (VHF channels 2. . . 4), one in band III (VHF channels S. . .12) and many of them will be in bands IV and V (UHF channels 21.. .69).

TV Transmitter Band I and III

This TV transmitter working on VHF Band I and III, using negative sound modulation and PAL video modulation. This is suitable for countries using TV systems B and G, like Australia and Indonesia.
This circuit has not been tested at UHF frequencies. The modulated sound signal contains 5.5 -6MHz by tuning C5. Sound modulation is FM and is compatible with UK TV Transmitter System I sound. The transmitter however is working at VHF frequencies between 54 and 216MHz (band I and Band III) and therefore compatible only with countries using Pal System B and Pal System G.

88-108 MHz Preamplifier

This VHF amplifier working on Band 2 Radio Spectrum tuning approximately 88 - 108 Mhz

The Preamplifier circuit uses two 2N3819 FET's in cascade configuration. The lower FET operates in common source mode, while the upper FET, operates in common gate, realizing full high frequency gain. The bottom FET is tunable allowing a peak for a particular station.
Coil details follow:
L1 4 turns of 18swg air spaced with a 1cm diameter, the tap is one turn up from earth end...
L2 4 turns of 18swg air spaced with 1 cm diameter. The coupling coil is 1 turn interwound from the supply end. Enamel coated wire must be used.

Making Simple TV transmitter

(1) Soundless version, You are familiar with the most simplest FM transmitter" that I designed (left). Let's try to transform it into a TV transmitter. Just change the input from the audio to the video (video camera or VCR) and check the signal at your television set: in Europe, for instance, choose the channel 2 - 4 and turn the trimmer cap of the transmitter. You will find some images or might watch a clear image. This suggests that it will be not so difficult to build a TV transmitter.

(2) Advanced Version (AV) , When you succeed in this version to work, you may try the advanced version (pdf). ( )
In this version, stability and quality are improved. This can have even the audio too. However, in order to complete this, you have to use a proper frequency counter.

FM Transmitter With Transistor 2SC1815

Will have to introduce a system of simple and small FM transmitter. Not only does it meet the requirements of the launch distance, but also at the same time using microphone and voice input signal line, background voice. Modulation circuit surveillance has also joined the table first, so that they can better control and the proper use of transmitters, the following circuit diagram, read briefly, whether it's just like a radio station equipment as many functions. Yes, this small transmitter can help you easily set up an amateur FM radio stations! 500 M in the coverage around. Echocardiography the bar, act immediately!
Principle small FM transmitter circuit components and options:

Signal to the microphone after intake, the C1 coupling into the BG1 and external circuit voltage of the single negative feedback amplifier, the voltage signal amplification weak enough to enlarge the extent of U1A and the line to enter the input signal with a mixed U1B. Mixed signal modulation way to the R17 from BG2 FET and the surrounding circuit composed of common than LC finishes the test, the test than the LC oscillator are characterized by a general three-capacitance oscillator simple, but also with high efficiency and high stability. Waveform, and modulation bandwidth, as this amateur production of FM transmitters appears to be particularly important.

Finally BG3 cast by the post-amplifier to enlarge the field by launching antenna fired by general can listen to FM radio broadcast. Another component of the signal through the amplifier to enlarge U1C after the wave rectifier D2 SR DC drive microamps table, Near and surveillance signal modulation rate. Use the system for general should not exceed 85 per cent suitable. GM and other integrated circuits using LM324 four operational amplifier and form a single power reverse input, both of the input voltage is set at half the supply voltage. Table surveillance for the first u-200, BG1.BG3 choose 2SC1815. BG2 three DO2 FET, D2 varactor diode using a S2267. Antenna require the use of 1 / 4 wavelength, such as the use of the best pull rod antenna not less than one metre. Otherwise effect will be less than overstaying launch. Final say about, please do not interfere with normal radio!

FM transmitter With uPC1651

The circuit has been produced by Japan's NEC as a major upc1651 IC devices, the high gain circuit, work stability, thereby ensuring the microphone performance. Use of FM transmitter. Used it 40 - 50 cm soft drag line for antenna, the effective range of more than 30 launch M. L carefully spacing adjustment and fine-tuning capacitor, will launch frequency coverage for 88 - 108 Mhz. Map L enameled wire with diameter of 0.51 mm in diameter, 4 mm cylindrical Tuitai from around 5 laps

FM Stereo Encoder CD4066

Circuit schematics IC1-4069 in the Y1, Y2 formation of a 76 KHZ frequency of the oscillator, the Y3-Y6 isolation plastic, into IC2 dual JK flip-flop CD4027 composed of two components- frequency circuit, a symmetrical + / 38KHZ-19 KHZ and the square wave, + / -38 KHZ IC3 the square used to control analog switches CD4066, a stereo audio input signal after switching modulation used for the 19 KHZ frequency mixed signal to the transistor into FM 9014 after isolation Modulator.
Click to access the debug FM modulator and 5 V power supply, with a multimeter measured IC1CD4069 the legs and IC2 CP, Q, Q, the legs should be half the supply voltage, the oscillator has been start-up. If a digital frequency meter measured IC1 output frequency, frequency regulation RW1 to 75 KHZ + /-10HZ can. If not, can be transferred to the prospective radios, RW2 half-good, and then transferred RW1, the bright lights stereo radio, and no speakers in the temple frequency whistle sounds. From the input into the stereo audio signal (1.5 Vpp, output amplifier available), this will be able to receive stereo radio broadcasting.

Input signal can be obtained from the line, but at R7 should be changed. Finally, can be transferred R7 to the smallest high-frequency noise, in fact R6, R7 equivalent BA1404 in 13, 14 feet of external components, the Pilot mixed signal and composite signal circuits, and input to the amplifier, the circuit of is 9014, and BA1404 from 12 feet on the entry.

Macsot MR-700 High Quality wireless microphone

This is collected by the Macsot MR-700 wireless microphone system launch of the circuit for maintenance reference. High Quality Audio on receiver output.
Active components:
  • Microphone or Audio Preamplifier with IC MC4458
  • Dynamic Audio processed with one NE571 From Philips
  • Frequency Oscillator generated by one crystal 20.05 MHz and Varactor diode 2CB11A. No drift frequency is guaranted.
  • 9V DC power supply or battery.

FM Stereo Transmitter With MC145151

This fm stereo transmitter use pll chip MC145151 from Motorola and stereo encoder chips BA1404 with vco built in. MC145151 IC used is to overcome the single-frequency instability in the BA1404. Modulation of the emission control BB910 frequency. B571C kept in control procedures, the procedures required to prepare another.

Parts List and Schematic

Component Values of the fm stereo transmitter you can find out the schematic. Please download schematic for enlarged image

Amplifier section of this FM Stereo transmitter uses a single 2sc2053 transistor with power out about 250 mWatt.