Audio Relay Switch


This circuit is designed to receive a line output from a computer and, if the frequency falls within the appropriate range, power one of four relays. The line inputs are each run through an RC bandpass filter into peak detector, which is then connected to the positive terminal of an op-amp comparator. If the peak detector exceeds a certain voltage (adjustable), the comparator will activate the relay. Up to four signals may be operated simultaneously, activatig all of the relays independently.


The circuit was ultimately successful. The relays behaved as intended, switching very cleanly and quickly when the target frequency was received. Initially there was some difficulty as one of the relays broke after soldering. Half of the board needed to be unsoldered and resoldered in order to find it. This resulted in a very messy soldering job, but a functional design. The device sometimes had difficulty switching all four relays at once, and the relays may trigger each other if the reference voltage is improperly calibrated.


The device performed remarkably well. If I were to rebuild, I would have used a bigger circuit board so as not to layer PCBs. The layering process created unnecessary complications for space and worsened the build quality. The target frequencies should have been spaced more evenly to provide a greater overall voltage tolerance.