This project is an Application/extension of Digital Pulse Counter.
Transmitter Part: The transmitter circuit (see Fig. 1) is built around timer NE555 (IC1), which is wired as an astable multivibrator producing a frequency of about 38 kHz. The infrared (IR) beam is transmitted through IR LED1.
HERE A is +9V and B is GND.
Receiver Part: There are two 7 segment displays driven by two CD4026B (CMOS DECADE COUNTER/DIVIDER) used here to count up to 99. Seven Segment display used are common cathode type(see fig below).
Moving ahead when the transmitted signal is cut, Pulses are generated by the IR receiver TSOP1738. The output of TSOP1738 is then fed to monostable multivibrator circuit made using NE555. Then the controlled stable pulse of 250ms (T=1.1*R*C) is fed to CD4026B which will drive the unit place display to make it count from 0 to 9. When it overflows, carry is generated by this IC and this carryout is fed to another CD4026B driving Tens Place display . Thus making the whole circuit count 0 to 99. Similar CD4026 circuit can be added to increase the number of counts.
This Circuit has various applications such as spring oscillation counting, Counting no of people entering through door(one way), as a bugular alarm, etc.
Here you can download the PDF Schematic of the receiver part.
The range of this FM transmitter is around 100 metres at 9V DC supply.
Fig. 1: FM transmitter
The circuit comprises three stages. The first stage is a microphone preamplifier built around BC548 transistor. The next stage is a VHF oscillator wired around another BC548. (BC series transistors are generally used in low-frequency stages. But these also work fine in RF stages as oscillator.) The third stage is a class-A tuned amplifier that boosts signals from the oscillator. Use of the additional RF amplifier increases the range of the transmitter.
Coil L1 comprises four turns of 20SWG enamelled copper wire wound to 1.5cm length of a 4mm dia. air core. Coil L2 comprises six turns of 20SWG enamelled copper wire wound on a 4mm dia. air core.
Fig. 2: Pin configurations of transistors BC548 and C2570
Use a 75cm long wire as the antenna. For the maximum range, use a sensitive receiver. VC1 is a frequency-adjusting trimpot. VC2 should be adjusted for the maximum range. The transmitter unit is powered by a 9V PP3 battery. It can be combined with a readily available FM receiver kit to make a walkie-talkie set as shown in Fig. 3
Fig. 3: Walkie-talkie arrangement
I have used earphone speakers in replacement for condenser mic providing more portability.
COURTESY: ELECTRONICS FOR YOU