baracuda rev A silverdog bad performance

[rdz28]

hello to all, I built the geotech baracuda step by step and I stuck in step 7 (I do not have an oscilloscope) I could not adjust the voltage to -2.1v so I welded an adjustable resistor instead of the resistance R20, so I managed to adjust to 2.1V .. the problem is that a hammer detects it at 13cm and a coin at 2cm.the coil is 20cm with 26 turns of 0.50mm thread, the resistance r1 is from 100ohm

[waltr]

Did you SHORT PL2?
If so and you have a 100 Ohm at R1 then possible damping is too much and signal not ready at the minimum delay.

R20 must Match the value of R19 else the integrator will be un-balanced. That is NOT the correct method to adjust the Output Voltage of U7, pin 1 .

You really should use an O'scope to do Step #6.
See if you borrow an O'scope and re-do Step #6.

[rdz28]

then restore the resistance of R20 ..I try to put the 390 back on r1?I do not know anyone who has an oscilloscope

[homefire]

Try a local high school. They may have a Electronics class or the like that use them.

[rdz28]

how about trying PC software with sound card?

[kosacid]

buy a DSO kit they are cheap and work great for what you need it for

[rdz28]

guys, before buying a kit dso I built a probe with a 3.5 jack, a 100uf capacitor, and a 10k potentiometer .. I downloaded a program on the PC called visual analyzer, now I explain how I should do to calculate the card values and where?

[waltr]

guys, before buying a kit dso I built a probe with a 3.5 jack, a 100uf capacitor, and a 10k potentiometer .. I downloaded a program on the PC called visual analyzer, now I explain how I should do to calculate the card values and where?

That should work fine. First thing is to Measure the Frequency of the pulsing and then the Delay times and pulse widths as per step #6.
If these are not correct then no hope of the analog circuit working.

Next is looking at the output of the Pre-amp and adjusting the Damping resistor value.

[rdz28]

these are the tests for step 6 .. I do not know if it's right I can not use the oscilloscope

[kt315]

I stuck in step 7 (I do not have an oscilloscope)
--
is step 7 preamp balance? what you mean?

[rdz28]

at point 7 I was stuck because I could not change the voltage, I downloaded a software on the PC and I built a probe to take advantage of the PC sound card .. I did the tests on u4 on pins 6-8-10 and those are the results, but I've never used an oscilloscope I do not know how to read or how to use it

[kt315]

if you need to measure voltage on preamp output desolder mos-fet. without signal you have to see DC voltage and balance tuning is nulling it to zero.
you do not need o-scope.

[rdz28]

and I do not have to check the values on u4 if they are right? also because I can not adjust the first pin of u7 to -2.1V and the search depth is too low

[Andi68]

Something is wrong

[rdz28]

I know but I do not understand what .. I did everything as the guide said .. but I still can not adjust u7