Custom Search

Monday, February 11, 2008

Remote control using telephone

Here is a teleremote circuit which enables switching ‘on’ and ‘off’ of appliances through telephone lines. It can be used to switch appliances from any distance, overcoming the limited range of infrared and radio remote controls.
The circuit described here can be used to switch up to nine appliances (corresponding to the digits 1 through 9 of the telephone key-pad). The DTMF signals on telephone instrument are used as control signals. The digit ‘0’ in DTMF mode is used to toggle between the appliance mode and normal telephone operation mode. Thus the telephone can be used to switch on or switch off the appliances also while being used for normal conversation.

The circuit uses IC KT3170 (DTMF-to-BCD converter), 74154 (4-to-16-line demult-iplexer), and five CD4013 (D flip-flop) ICs. The working of the circuit is as follows.
Once a call is established (after hearing ring-back tone), dial ‘0’ in DTMF mode. IC1 decodes this as ‘1010,’ which is further demultiplex ed by IC2 as output O10 (at pin 11) of IC2 (74154). The active low output of IC2, after inversion by an inverter gate of IC3 (CD4049), becomes logic 1. This is used to toggle flip-flop-1 (F/F-1) and relay RL1 is energized. Relay RL1 has two changeover contacts, RL1(a) and RL1(b). The energized RL1(a) contacts provide a 220-ohm loop across the telephone line while RL1(b) contacts inject a 10kHz tone on the line, which indicates to the caller that appliance mode has been selected. The 220-ohm loop on telephone line disconnects the ringer from the telephone line in the exchange. The line is now connected for appliance mode of operation.

If digit ‘0’ is not dialed (in DTMF) after establishing the call, the ring continues and the telephone can be used for normal conversation. After selection of the appliance mode of operation, if digit ‘1’ is dialed, it is decoded by IC1 and its output is ‘0001’. This BCD code is then demultiplexed by 4-to-16-line demultiplexer IC2 whose corresponding output, after inversion by a CD4049 inverter gate, goes to logic 1 state. This pulse toggles the corresponding flip-flop to alternate state. The flip-flop output is used to drive a relay (RL2) which can switch on or switch off the appliance connected through its contacts. By dialing other digits in a similar way, other appliances can also be switched ‘on’ or ‘off.’

Once the switching operation is over, the 220-ohm loop resistance and 10kHz tone needs to be removed from the telephone line. To achieve this, digit ‘0’ (in DTMF mode) is dialed again to toggle flip-flop-1 to de-energise relay RL1, which terminates the loop on line and the 10kHz tone is also disconnected. The telephone line is thus again set free to receive normal calls.This circuit is to be connected in parallel to the telephone instrument

Radio Remote Control using Dual Tone Multi Frequency (DTMF)

Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances. This remote control unit has 4 channels which can be easily extended to 12. This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals. Usually remote control circuits make use of infrared light to transmit control signals.
Their use is thus limited to a very confined area and line-of-sight. However, this circuit makes use of radio frequency to transmit the control signals and hence it can be used for control from almost anywhere in the house. Here we make use of DTMF (dual-tone multi frequency) signals (used in telephones to dial the digits) as the control codes. The DTMF tones are used for frequency modulation of the carrier. At the receiver unit, these frequency modulated signals are intercepted to obtain DTMF tones at the speaker terminals. This DTMF signal is connected to a DTMF-to-BCD converter whose BCD output is used to switch-on and switch-off various electrical appliances (4 in this case).

The remote control transmitter consists of DTMF generator and an FM transmitter circuit. For generating the DTMF frequencies, a dedicated IC UM91214B (which is used as a dialler IC in telephone instruments) is used here. This IC requires 3 volts for its operation. This is provided by a simple zener diode voltage regulator which converts 9 volts into 3 volts for use by this IC. For its time base, it requires a quartz crystal of 3.58 MHz which is easily available from electronic component shops. Pins 1 and 2 are used as chip select and DTMF mode select pins respectively. When the row and column pins (12 and 15) are shorted to each other, DTMF tones corresponding to digit 1 are output from its pin 7. Similarly, pins 13, 16 and 17 are additionally required to dial digits 2, 4 and 8. Rest of the pins of this IC may be left as they are. The output of IC1 is given to the input of this transmitter circuit which effectively frequency modulates the carrier and transmits it in the air. The carrier frequency is determined by coil L1 and trimmer capacitor VC1 (which may be adjusted for around 100MHz operation).

An antenna of 10 to 15 cms (4 to 6 inches) length will be sufficient to provide adequate range. The antenna is also necessary because the transmitter unit has to be housed in a metallic cabinet to protect the frequency drift caused due to stray EM fields. Four key switches (DPST push-to-on spring loaded) are required to transmit the desired DTMF tones. The switches when pressed generate the specific tone pairs as well as provide power to the transmitter circuit simultaneously. This way when the transmitter unit is not in use it consumes no power at all and the battery lasts much longer. The receiver unit consists of an FM receiver (these days simple and inexpensive FM kits are readily available in the market which work exceptionally well), a DTMF-to-BCD converter and a flip-flop toggling latch section. The frequency modulated DTMF signals are received by the FM receiver and the output (DTMF tones) are fed to the dedicated IC KT3170 which is a DTMF-to-BCD converter. This IC when fed with the DTMF tones gives corresponding BCD output; for example, when digit 1 is pressed, the output is 0001 and when digit 4 is pressed the output is 0100. This IC also requires a 3.58MHz crystal for its operation. The tone input is connected to its pin 2 and the BCD outputs are taken from pins 11 to 14 respectively. These outputs are fed to 4 individual ‘D’ flip-flop latches which have been converted into toggle flip-flops built around two CD4013B ICs. Whenever a digit is pressed, the receiver decodes it and gives a clock pulse which is used to toggle the corresponding flip-flop to the alternate state. The flip-flop output is used to drive a relay which in turn can latch or unlatch any electrical appliance.

We can upgrade the circuit to control as many as 12 channels since IC UM91214B can generates 12 DTMF tones. For this purpose some modification has to be done in receiver unit and also in between IC2 and toggle flip-flop section in the receiver. A 4-to-16 lines demultiplexer (IC 74154) has to be used and the number of toggle flip-flops have also to be increased to 12 from the existing 4

Tuesday, February 5, 2008

Ultrasonic Pest Repellent

It is well know that pests like rats, mice etc are repelled by ultrasonic frequency in the range of 30 kHz to 50 kHz. Human beings can’t hear these high-frequency sounds. Unfortunately, all pests do not react at the same ultrasonic frequency. While some pests get repelled at 35 kHz, some others get repelled at 38 to 40 kHz. Thus to increase the effectiveness, frequency of ultrasonic oscillator has to be continuously varied between certain limits. By using this circuit design, frequency of emission of ultrasonic sound is continuously varied step-by-step automatically.

One Button Digital On-Off Switch

The load is driven by the MOSFET IRFZ44 and 4093 AND gates are used in the circuit. The output of the 4093 IC drives the MOSFET. Only one button allows you to change the on-off state of the electronic circuits in which you use this switch. The circuit schematics is above. Click image to see the larger schematics diagram.

Count Down Timer

Timer kits are an ever popular item with the hobbyist. One of the main methods used is the ever-popular 555 timer IC. In this circuit we use a 555, a counter IC and a transistor switch to activate a relay either on-to-off or off-to-on (mode selected by a jumper) as soon as the counting period is over. Let us look at the kit in more detail. The circuit consists of 3 parts: an oscillator, a ripple counter and two switching transistors.

Telephone Receiver

An interesting circuit for a me- dium performance handy electronic telephone receiver, suited for receiving incoming calls, is described here. This circuit can be connected to almost all types of telephone exchange lines. To simplify the gadget, the dialler section has been omitted. The circuit can be constructed on a medium size veroboard. Wiring and components layout are not very critical. For compactness, enclose the wired circuit in a plastic cabinet as shown in Fig.(a) here. In order to prevent undesired acoustic feedback, it is necessary to adjust the orientation of ear-piece (LS) and mouth-piece (MIC) at the final stage of construction. The circuit consists of four sections: ringer, voltage regulator, transmitter and receiver. The ringer section is built around capacitor C1, resistor R1 and electronic buzzer BZ1.

500W Mos-Fet Power Inverter from 12V to 110V/220V

500W Mos-Fet Power Inverter from 12V to 110V/220V

This circuit will provide a very stable "Square Wave" Output Voltage. Frequency of operation is determined by a pot and is normally set to 60 Hz. Various "off the shelf" transformers can be used. Or Custom wind your own FOR BEST RESULTS. Additional MosFets can be paralleled for higher power. It is recommended to Have a "Fuse" in the Power Line and to always have a "Load connected", while power is being applied. The Fuse should be rated at 32 volts and should be aproximately 10 Amps per 100 watts of output. The Power leads must be heavy enough wire to handle this High Current Draw!
Appropriate Heat Sinks Should be used on the RFP50N06 Fets. These Fets are rated at 50 Amps and 60 Volts. ** Other types of Mosfets can be substituted if you wish. The LT1013 offers better drive that the LM358, but its your choice. The Power transformer must be capable of handling the chosen wattage output. Also, Appropriate Heat Sinks are Necessary on the Mos-Fets. Using a rebuilt Microwave transformer as shown below, it should handle about 500 watts Maximum. It requires about 18 turn Center-Tapped on the primary. To handle 500 watts would require using a 5 AWG wire. Pretty Heavy Stuff, but so is the current draw at that power.

12V to +/- 30V DC to DC Converter

This is a DC to DC converter for car power amplifier. 12V input generates +30V and -30V output for preamp or power amplifiers. Circuit uses SG3525 IC, Mosfets and switching power supply.

Active Antenna AA-7 HF/VHF/UHF, 3-3000MHz

If you have a shortwave or high-frequency receiver or scanner that is struggling to capture signals with a short, whip antenna, and you'd like the kind of performance that a 60-foot 'longwire' antenna can provide but lack the space to put one up, consider building the AA-7 HF/VHF/UHF Active Antenna described in this article. The AA-7 is a relatively simple antenna that is designed to amplify signals from 3 to 3000 MegaHertz, including three recognized ranges: 3-30Mhz high-frequency (HF) signals; 3-300Mhz very-high frequency (VHF) signals; 300-3000MHz ultra-high (UHF) frequency signals. Those bands are typically occupied by shortwave, ham, government, and commercial radio signals.

Active Antenna

An antenna with an integrated RF pre - amplifier

Monday, February 4, 2008

VHF/UHF TV Modulator

VHF/UHF TV Modulator

Simple oscillator that generates a frequency in the VHF or UHF region. The oscillator 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 TV to the correct frequency.

VHF Audio Video Transmitter

UHF-TV Preamplifier

Telephone FM Transmitter

Telephone FM Transmitter

This FM transmitter attaches in series to one of your phone lines. When there is a signal on the line (that is, when you pick up the handset) the circuit will transmit the conversation. In particular it will radiate from the phone line itself. It is a passive device - there is no battery. It uses the signal on the phone line for power. No aerial is needed - it feeds back the RF signal into the phone line which radiates it in the FM band. The frequency of transmission may be adjusted by the trimcap.L1 is 6 turns of enameled wire, L2 is 8 turns and L3 is 6 turns. Spread out L3 coil about 1 mm apart. The coils should not touch. A solder connection (or tap) is required from the top of the first turn in the L3 coil to the pad next to the coil. Solder a piece of wire to the top of the first turn as shown on the overlay. Then solder the other end to the pad immediately next to the L3 coil. R1 & C4 act as a low pass filter. C3 is a high frequency shunt. L2 is a RFC (radio frequency shunt.) It decouples the power and audio from the transmitter amplifier circuit. L1 and C6 should be adjusted to match a frequency on your FM receiver. With C1 at 27p you will find that the kit tunes into the FM band in the 86 - 95 MHz area. With C1 at 22p the band is raised to about 90-95mhz (depending in the coil spacing.) If you want to move this tunable area still higher to over 100MHz range then replace C1 by a 15pF or 10pF capacitor. You can experiment to get greater transmission range away from the phone line by adding an aerial (about 150 cm of 26 gauge wire) to the collector of T2.

TV Transmitter

TV Transmitter

A VHF band TV transmitter using negative sound modulation and PAL video modulation. This is suitable for countries using TV systems B and G.

Simple RF Power Meter

Simple RF Power Meter

Here is a simple set up which will enable them to measure the out put power of their transmitter. All that they require is a good multimeter which has a sensitivity of 20k ohms/4 Watts which is adequate for low power transmitters. Many beginners trying out their skill with QRP TX, for the first time have to overcome many problems before they are able to come on the air. On usual complaint is that, every thing is working fine but the signal is not going out.

The 8k resistor should be kept close to the out put terminal of the transmitter. Switch on the transmitter in the CW mode and measure the DC voltage with the multimeter. If the voltage is V then the out put power is given by Power = V^2/50

Radio Remote Control using DTMF

Radio Remote Control using DTMF

Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances. This remote control unit has 4 channels which can be easily extended to 12. This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals. Usually remote control circuits make use of infrared light to transmit control signals. Their use is thus limited to a very confined area and line-of-sight. However, this circuit makes use of radio frequency to transmit the control signals and hence it can be used for control from almost anywhere in the house.

Here we make use of DTMF (dual-tone multi frequency) signals (used in telephones to dial the digits) as the control codes. The DTMF tones are used for frequency modulation of the carrier. At the receiver unit, these frequency modulated signals are intercepted to obtain DTMF tones at the speaker terminals. This DTMF signal is connected to a DTMF-to-BCD converter whose BCD output is used to switch-on and switch-off various electrical appliances.

CB Transmitter

CB Transmitter

For the regulation it needs a voltmeter (with needle better) and charge 50W/5W. Connect charge 50W in the place of aerial, with the voltmeter in the exit voltmeter. Be supplied the transmitter with + 12V. It will be supposed we have consumption between 0,7-1A. With a screwdriver we regulate the core of inductor L1/L2 and later the variable C6 until we see the biggest tendency. We connect the microphone and speaking we observe the clue in the multimeter. If all have become right will be supposed the tendency, speaking, to go up roughly 30-35%.

5 Watt UHF TV Amplifier

This small circuit is a Linear amplifier for driving small UHF TV transmitters. Its gain is 7dB and can amplify a signal between 450-800 MHz. You can drive the circuit with 1 to 1,5 Watts signal. Better use double layer PCB with the second layer connected to earth. Use a stabilized power supply 25 volts and at least 5Amps. The transistor case is the SOT-122A and be careful because the transistor is very toxic for your health. Tuning can be achieved turning the two variable capacitors. Do not forget to use heat sink for both transistors, specially for the BLW89 and it would be better if you place a small fan as well.

400mW VCO FM transmitter

With good antenna (dipole placed outdoor and high) the transmitter has very good coverage range about 500 meters, the maximal coverage range is up to 4 km.

3V FM Transmitter for 88MHz to 108MHz

3V FM Transmitter for 88MHz to 108MHz

The important part of the circuit is formed of the Colpitts type oscillator. C3,C4,C5,C6,CD1-CD2 and L1 determines the frequency. BF982 and dual gate MOSFET are active parts in oscillator. When the input impedance of the MOSFET gate inputs are high, LC tank is not affected. However transistors force the LC tank and cause phase shift. Two driver stages are added to isolate the antenna from oscillator. First stage (BF199) amplifies the low signal of the oscillator and works as a constant load. The second stage (BFR90) amplifies the signal going through the antenna some more. A short copper wire can be used as an antenna here. Attaching a large antenna to this circuit is unnecessary because the output power is low.

Notes: 1. Coil 1: Winding wire must be 1 mm thick and isolated. Number of turns: 3.5 . 5mm core must be used and the distance between each turn must be 1mm. 2. You can use BF199 instead of BFR90. 3. If you can't find the varicap diode, you can use MV104 instead.

25W RF amplifier

RF amplifier with 25W of power for 88-108MHz FM transmitters.

1W portable PLL transmitter

1W portable PLL transmitter

This small FM transmitter includes a limiter, a microphone amplifier and a PLL digital tuning. All the parts are placed on one circuit board. The RF power is switchable between 1W and 0,2W. The schematic diagram is divided into three parts: RF part (numbered from 1), PLL (numbered from 30) and audio part (numbered from 50).

15dB UHF TV Antenna Booster

15dB UHF TV Antenna Booster

This is an UHF band TV antenna preamplifier circuit With 15dB gain to build easily. It is formed based on BF180 UHF Transistor. The first stage is an band pass filter constructed by the C1, CV1, L1, L4, C7 and C3, the second stage is a base-common voltage amplifier with low input impedance to match. Build the L1 ~ L4 as air core coil to obtain high Q-Factor. After assembling, pack it into a proper metallic box and connect the ground of the circuit to the box to reduce noise effect.

1 Watt Universal RF Amplifier

Q1 Transistor: 2N5109, MRF227, 2N4427, 2N3866

Voltage Supply: 12 - 15V

This is a universal 1 Watt RF class C amplifier that is ideally suited for low power FM transmitters. Input should be at least 100mW to achieve 1W output. It is recommended to enclose the amplifier in a metal case.

0.1 - 3.5GHz Prescaler

0.1 - 3.5GHz Prescaler

This handy prescaler divides input frequency by 1000. It takes maximum input frequency of 3.5GHz and converts it into 3.5MHz that may be measured using standard frequency meter.

Single Chip FM Transmitter

IC1: MAX2606
L1: 390nH

Voltage Supply: 3 - 5V
Frequency: 88 - 108MHz


A simple FM transmitter links your home-entertainment system to a portable radio that can be carried around the house and into the back yard. For example, you can play music on the CD changer in your living room, and listen to it on a portable radio by the back-yard barbeque.

IC1 is a voltage-controlled oscillator with integrated varactor. Its nominal frequency of oscillation is set by inductor L1, and a 390nH value places that frequency at 100MHz. Potentiometer R1 then lets you select a channel by tuning over the FM band of 88MHz to 108MHz. Output power is about -21dBm into 50 (most countries accept emissions below 10dBm in the FM band).

The home system's left and right audio signals are summed by R3 and R4, and attenuated by the (optional) potentiometer R2. R2's wiper signal serves as a volume control by modulating the RF frequency. Signals above 60mV introduce distortion, so the pot attenuates down from that level.

In the absence of a standard FM radio antenna, 75cm (30 inches) of wire will suffice as a transmitting antenna. For best reception, it should be mounted parallel with the receiving antenna. The IC operates on a single supply voltage in the range 3V to 5V, but you should regulate the applied voltage to minimize frequency drift and noise.

1W Linear FM Booster

This RF Amplifier is used for boosting small fm transmiters and bugs. It use two Philips 2N4427 and its power is about 1Watt. At the output you can drive any linear with BGY133 or BLY87 and so on. Its power supply has to give 500mA current at 12 Volts. More voltage can boost the distance but the transistors will be burned much earlier than usual.! In any case do not exceed the 15Volts. The Amp offers 15 dB in the area of 80Mhz to 110 Mhz. L4, L5, and L6 are 5mm diameter air coils, 8 turns, with wire 1mm wire diameter.An easy project, with great results.

110VAC Inverter for Automobile

This circuit will allow you to operate small devices like laptop computers inside your automobile without an expensive automobile power supply. The circuit takes advantage of the fact that power transformers are linear devices and can be used to step up as well as step down. This is evident by the fact that the supply drives the secondary and the output is on the primary.

Warning: this supply produces dangerous and lethal voltages. Use extreme caution when testing this circuit. In addition, make sure the assembly is enclosed in a plastic case. Do not package this circuit in a metal or aluminum case!

The design depends on the windings ratio and the value of the car battery to produce an AC waveform of approximately 95 volts RMS. No filtering is performed on the secondary since the transformer blocks most of the sharp edges from the input waveform.

All of the devices (14013, 555, 14020, and 4049) should have their supply pins connected to the +12 supply. The nice thing about CMOS logic is that it will operate over a wide range of voltages. Before connecting the center tap of the transformer, adjust R3 until the signal on U5 pin 13 is 120Hz.

The 14013's are used to produce a 60Hz square wave with an accurate 50% duty cycle and to force the FET switches operate in a break-before-mate manner. The 4049's have enough drive capability to snap the FET's off and on very quickly.

12V To 220V 50Hz Inverter 50W by M706B1

Serial Port PIC Programmer for PIC16 & PIC18

Serial Port PIC Programmer
Schematic & Parts List
PIC 16F628A Firmware for 8, 10, 12, 16 & 20MHZ Clock Freq.
PIC 16F628 Firmware for 8, 10, 12, 16 & 16MHZ Clock Freq.
Download Free Serial Port Programming Software from Oshonsoft

Ponyprog Circuit for AVR & PIC16F84

All resistors are 1/4W.The circuit is powered by 9...15V DC or AC. When In Circuit Programming (ISP) connectors are used, is possible the programmer to be powered from target’s power source. Diodes D2 and D6 protect the regulator LM7805, when target’s power is used.

' XTAL JUMP ' is used to cut XTAL when the AVR has internal RC oscillator enabled.

'FAMILY JUMP' is used to select which ATMEL’s family to program, AVR series (ATtinyXX, AT90SXXXX, ATmegaXXX) or 8051 series (AT89Sxxxx).

‘PIC JUMP’ is used to switch between Microchip’s PIC and ATMEL’s microcontrollers. With jumper ON only PIC can be programmed, while OFF can program ATMEL’s microcontrollers. If you don’t need to program PICs, you can leave their board area unsoldered. The PCB has been designed so that DIP sockets or ZIF sockets can be used. Because of its cost, it is recommended that only one ZIF is used combined with some pin-arrays to switch between the four different places.

The board must be connected to a PC COM port through a 9 pin to pin cable and work with the below application:

'PonyProg2000 - Serial Device Programmer

ATMEL’s AVR series

ATtiny12, ATtiny15, AT90S1200, AT90S1200A, AT90S2233, AT90S2313, AT90S2323, AT90S2343, AT90S4414, AT90S4433, AT90S4434, AT90S8515, AT90S8535, ATmega8, ATmega16, ATmega161, ATmega163, ATmega323, ATMEL’s 8051 series, AT89S53, AT89S8252


PIC16x83, PIC16x84, PIC16F84A

And some other programmable ICs (memories, microcontrollers) which Ponyprog support but need a board adapter to be programmed through ISP connectors. For more information see Claudio Lanconelli site .