Rev A - Stuck in step 7

[kt315]

It detect's it at apporximately 3 cm: https://youtu.be/dj2eUcmOb6o
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you have strange zoom. you have to find a source of this. either it is a lamp or your voltage power source.
begin from small coil to use. very small. just do 300uH coil on ferrite rod.

[green]

Monitor U4 pin 5 with scope while adjusting R14 or sample delay pot. Should be fast to near -5v and then RC time constant going back to 0v. Time back to 0v should change with pot adjustment.