non-VCO problem

[1843]

Carl,

I have finished my third Hammerhead. Their detections are pretty good.
But all of them have a common problem in the output sound:
When an object becomes very close to the coil (less than 6cm for small objects), instead of its noise loudness becomes stronger, mutes (damps)...
It hasen't this problem with VCO option...

What do you think about this problem?

I am sure that problem is after IC8 because when HH detects the object, TP5 rises to +5V.
(When object is near the coil, TP9 has a square waveform)

Regards

[Carl-NC]

Don't recall seeing this... is SW2 closed? Check R51 & R38 values... if they're correct, try tacking another 10k in parallel to R51 & see if it helps.

- Carl

[1843]

Thanks Carl!
I changed R51 to 4.7K... The problem solved...