Another plea for help diagnosing a Surf PI board

[Kev]

The threshold circuit looks to be your Achilles.
Sort out your threshold and critically dampen your coil and you'll easily get nickels at 14 inches in the ground.

Look out here come the blisters..................:-)

P.S. If you do the trick with the trimmer best to use a 1k2 and a 10k trimmer, seems your coil is pretty fast so that will give you a bit more headroom.

Cheers

[gfcardi]

Thank you for all of your help. I appreciate it IMMENSELY!!

[Kev]

Hi gfcardi,
Just thought you might like a tip regarding resistor selection?
Say you found that you needed a damping resistor of 856 Ohms.
First take the reciprocal of this number (1÷ 856) and store that in your calculator memory. Then look at your resistor selection and select the first one above 856. Likely this will be 910. Take the reciprocal of this number and subtract it from the one you stored in memory. Now take the reciprocal of the result, which in this case is 14,425 or 14k425, now look at your resistors and see if you have one close to this, I doubt you will have, so repeat the scenario until your result comes close to a valid value

Example, (856^-1 - 1,500^-1 = 501.557^-06) ( 501.557^-06 ^-1 = 1,994 ) 1,994 is very close to 2k.
So a 2k in parallel with a 1k5 gives 857 Ohms
It is more accurate with E24 series and above. E12 is not quite as accurate.

Maybe you Majored in Maths and this is quite obvious to you, I'm sorry, I don't know your situation, but it might help someone else along the ways, as will all the scope shots you posted.

HH
Kev

[gfcardi]

Hi Kev!

That is a really clever trick. Thanks! I am always interested in learning how to do things faster and better.

Greg