Fault finding on surf PI with simple 386 audio amp

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I see people all the time struggling to find faults on their Surf PI projects
with out any real test gear.
Here is a simple idea, you can try and test a few points in the circuit with a simple 386 audio amp.

At least you can test the 555 output and a few of the gates.

First make sure that all the voltages to all of the IC's are correct,
connect up a simple 386 amp and probe around the pcb.

Here is a simple circuit I used for these audio files, these were made on a fully working
surf pi kit from Silverdog, the threshold was turned down to minimum.
You must use the latest schematic on Silverdog site for correct pin numbering.

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This mp3 file is the audio output of the Surf pi speaker with a coin being waved in front of it,
you can just here the threshold breaking.

[6666]

This mp3 is the tone you should hear on pin 3 of the 555.

You should also hear the same tone at Test point 1 and test point 2
and pin3 U4A and pin4 U4B .

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This is what you should hear on pin 8 UC4.

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This is the latest schematic from Silverdog.

[bernte_one]

very cool

many thanks