Wiring Diagram Remote Control

This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor. ( Click here for Colpitt Oscillator Resonant Frequency Equation.) Frequency is around 100Mhz with values shown.

4 Transistor Transmitter Circuit Diagram

Audio modulation is fed into the tank circuit via the 5p capacitor, the 10k resistor and 1N4002 controlling the amount of modulation. The oscillator output is fed into the 3.9uH inductor which will have a high impedance at RF frequencies.

The output stage operates as a class D amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.

24 Volt DC is a very prevalent voltage used fashionable developed settings. This hobby circuit lower was designed to acknowledge four unlike 24v DC alarm input signals, which are followed by used to drive a single low power beeper. The beeper is a magnetic type with its own oscillator/driver. The four diodes form an “or else” gate so one solitary of the four inputs want cause the beeper to produce blast. A CMOS version of the widely held 555 timer is used to strobe the beeper on and rancid on something like 1Hz.