Above diagram is a very easy and efficient receiver for actuating garage doors, starter motors, alarms, warning systems and many some other possibilities. The SCR, which has a extremely low trigger current of 30 uA is typical — it demands an input electricity of just 30 uW to activate the relay. A high Q tuned antenna circuit assures rejection of spurious signals. A whip or wire antenna is adequate as much as 100 feet from a low power transistor transmitter. A momentary-off switch resets the circuit.
The circuit specifies a whip or wire antenna which just means a solid piece of wire 6-12 inches lengthy (15-30cm). The antenna coil is experimental, however you are able to begin with ten to 12 turns of #22 (0.7mm) magnet wire, and 5/16″ (8mm) coil diameter. Antenna wire is soldered at 1/2 turn of the coil and the gate of the BRY35 is soldered about halfway the coil. This circuit will transmit as much as 100-feet with the above specifications @ 30uA.
The relay coil is specify’s as much as 200 ohm but that’s only the one I had in stock. Any low-ohm relay, even at 9V or so, should work. And a remaining note, do not count on too much with this circuit. The “Simplest R/C Circuit” is just that; Easy!
The BRY35 is really an classic semiconductor made by Philips. A good alternative could be the EC103D1, also produced by Philips (see pin-out picture for this device). NTE Semiconductors gives an alternative of NTE5405, but I’ve not attempted it. I believe, a NTE5400 (30V) or NTE5401 (60V) will work just also. The NTE5405 is a bit overkill at 400V.