[sdiy] Jack insertion detection

[Tim Ressel]

Hello supremely helpful folks!

I've got another challenge: how to detect when a plug is inserted into a 
jack. These are 3.5mm mono jacks btw. The current method is to use a 
stereo jack. When a mono plug is inserted the ring connection gets 
shorted to ground by the sleeve of the plug. This method works well, but 
the stereo jacks are taller than the mono jacks.

The only jack I can use is a switched mono jack where switched port is 
tied to the tip port until a plug is inserted. My idea is to use the 
switch port to feed an out of range voltage to the tip port, probably a 
negative voltage. Then use a comparator to detect when the tip port goes 
high.

Any other thoughts?

-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com