How do i wire a 3.5mm audio headphone jack?


#1

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.

Thanks!

1: https://8bitworkshop.com/v3.4.0/?platform=verilog&file=sound_generator.v
2: http://store.gadgetfactory.net/audio-wing/


#2

The correct way to do things is to follow the circuit diagram here - https://github.com/gundy/tiny-synth.

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 https://forum.mystorm.uk/t/documentation-for-electrical-limitations-of-io-pins-pmods/528

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