Monday, February 11, 2008
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
Monday, February 4, 2008
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.
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
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.
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.
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.
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
'PonyProg2000 - Serial Device Programmer
ATMEL’s AVR series
MICROCHIP’s PIC series
PIC16x83, PIC16x84, PIC16F84A