Surf Pi parasite sound

[nebulos]

Hello everyone,

Thanks to some free time these days I'm coming back to this old project of building a Surf Pi 1.2!
I purchased a PCB and soldered the components I bought on my side.

It works! Meaning some improvements remain to be done (potentiometers adjustments, and probably a new coil like mine is currently about 260 ?H only), but it detects coins. However one thing I cannot figure out is the noise the detector is making when there is nothing to detect (even in a wave free environment). I obtain a clear signal when the detector rings but 2 seconds after the silence turns back to an irregular noise. It can be silent using the tune potentiometer, but I'm not sure it indicates a clean working state.

One clue I have is the ICL7660 Vout, which looks weird to me.
I've try to change (all) the ICs, but nothing changed.
I've try to built the ICL7660 with the same configuration on a breadboard, and I have the same signal.


Does anyone have an idea?
Is this irregular noise normal?
Is this ICL7660 output signal normal?

Best,
Anthony

[Vadim18]

Hi nebulos!
Check your battery voltage first, it must be more than 11V, or you will get random beep-beep signals.
260uH coil is absolutely normal for Surf PI, almoust like in original.
And don't use any Ethernet UTP cable wires for coil, because they all bimetal.