On-Air Sign with RF Relay Images

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On-Air Sign with RF Relay Schematic

Construction Notes

This is a very simple circuit that has a voltage doubling detector feeding an OpAmp. The OpAmp has a gain of 50 and in turn drives a Darlington Transistor that toggles a relay. The circuit is built on a Protoboard with point to point wiring and the board was mounted inside the On-Air Display. Nothing about this circuit is too crotical but try to keep all leads as short as possible. You can use almost anything as an antenna. A long piece of wire will work real well. I had a lot of the parts in my junk box and I bet you do too. The whole project should cost under $100 maybe much less if you have a well stocked junk box as is very easy to build. The most important thing is to learn something and have fun building this very useful device. Why not give it a try? Drop me a line if you find this project helpful or have any questions.

On-Air Sign with RF Relay Parts list

.01 uF Capacitor (Quantity 2) Digikey .01 uF Capacitor Image $0.31
1N34A Germanium Diode (Quantity 2) Newark 1n34a Image $3.76
10K Ohm Potentiometer Digikey 10K Potentiometer Image $0.79
2.7K Ohm 1/4 Watt Resistor Digikey 2.7K Resistor Image $0.10
100K Ohm 1/4 Watt Resistor Digikey 100K Resistor Image $0.10
1K Ohm 1/4 Watt Resistor Digikey 1K Resistor Image $0.10
LM324N Quad Operational Amplifier Digikey LM324N Image $0.57
MPSA13 Darlington Transistor Digikey MPSA13 Image $0.42
Nichicon UVR1E102MPD 1000 uF 25 Volt Capacitor Digikey 1000 uF Cap Image $0.44
Panasonic JS1-12V-F 12 Volt Relay Digikey JS1-12V-F 12 Image $1.67
PCB Terminal Block (Quantity 2) Mouser PCB Terminal Block Image $1.69
PR1593L Protoboard 2-Hole Pads Amazon PR1593L Protoboard Image $5.50
340 Studio Warning Light Broadcasters On-Air Warning Image $80.00

Project Downloads

RF Relay Schematic (AutoCad .DWG File) Click here to Download
RF Relay Schematic (Adobe .PDF File) Click here to Download