How do i wire a 3.5mm audio headphone jack?


Hi there,

i would like to implement this soundchip[1] for real, but i don’t know how to wire a mono 3.5mm audio headphone jack to the FPGA to get any audio output (the ‘spkr’ pin in that Verilog project[1]) - GND goes to GND (of course), but what about the SIGNAL pin? Can i feed it directly to any FPGA pin without worrying about impedance, voltage / current levels, etc?

I’ll probably use a pair of wired earphones or a couple of small speaker to test the audio output, FWIW.

Moreover, i have one of this[2] laying around but i can’t find the schematics, it would be awesome if someone can tell me how to wire it to the FPGA.




The correct way to do things is to follow the circuit diagram here -

In practice, with most speakers or earphones, you can omit the low-pass filter capacitors, without any noticeable change in audio quality.

Personally, I also omit the resistor without any problem so far. That may risk damaging the FPGA pin, but the pins have non-linear current output so don’t seem to get damaged in practice - see

If you use that Audio Wing device, it will have the low-pass filter and current limiting resistor built in.