I use my raspberry 1 B+ with a DAC board (like hifiberry) and volumio/moode audio distribution.
The board is working as a pre-amp and it's connected to my hifi amplifier RCAs input, sending analog audio signals.
My raspberry is powered on all day long. As now I have to manually go to the amp and power it on (and off)...
My amplifier has a 3.5mm mono connector labeled "trigger input" (the manual says it works 3-30v AC or DC). That connector allows to turn on and off the amplifier remotely from a master device. You turn on the master device and the amp receives the signal and it wakes up from standby. I measured that if there is voltage it stays on, if <2.1v DC it goes into standby.
I tried sending with 3.0v DC from a lab power supply and it works as I want. Well it works as long as >2.1v DC. So it should work even from raspberry GPIOs. I measured the amp trigger input was pulling only 0.70/1mA at 3.0v DC and it worked perfectly.
I would like to drive this from the raspberry GPIO, with a script that fetch MPD status, and if not playing it should set the GPIO pin to low (0v) after 10 minutes of inactivity, thus turning off the amp. The script is not a problem, already found one and works.
The problem is the circuit, being electronic noob don't want to damage the raspberry.
- Can I drive it directly from the GPIO (e.g. without a relay) being only 1mA load? I can hear the amp has a relay that clicks when i send voltage to that trigger, so it should be only relay's coil load?
- How can I protect the gpio from shorts (e.g. pulling out the 3.5mm connector while ON) and eventual overvoltage(that shouldn't happen as there's no current on the amp side being an input, but don't know the circuit)
I have a load of passive components around, can solder, just can't design circuits.