Stuck in step 3

[green]

More likely I misspoke It certainly would not be the first time. I suppose that I could watch the video to confirm but I am supposed to be working on my spreadsheets.
Cheers

Maybe the circuit worked better underdamped.

[surfdetector]

Maybe I miss understood when you stated the coil inductance?

More likely I misspoke It certainly would not be the first time. I suppose that I could watch the video to confirm but I am supposed to be working on my spreadsheets.
Cheers

[green]

The video was meant more to be a 30,000 Ft view of what the overall waveforms look like for those who had never seen them before rather than an attempt to match the results of the Rd formula. That being said, I don't actually recall which coil I was using for the video however it certainly wasn't anything as low as 200uH as all of mine are much higher and none of them are fast coils.
Cheers

Maybe I miss understood when you stated the coil inductance?

[surfdetector]

Watched the video. I find Rd=pi*L*F usually comes close to critical damped. Looks like your oscillation was around 235kHz(3.14*200uH*.235MHz=148ohms). 148ohms quite a bit different than 360ohms. Is the coil really underdamped or am I missing something?

The video was meant more to be a 30,000 Ft view of what the overall waveforms look like for those who had never seen them before rather than an attempt to match the results of the Rd formula. That being said, I don't actually recall which coil I was using for the video however it certainly wasn't anything as low as 200uH as all of mine are much higher and none of them are fast coils.
Cheers

[green]

You might find it of interest to watch these two videos that I did on the damping resistor jig and adjusting:
https://youtube.com/playlist?list=PL...7Rd5MniTrONUBI

Watched the video. I find Rd=pi*L*F usually comes close to critical damped. Looks like your oscillation was around 235kHz(3.14*200uH*.235MHz=148ohms). 148ohms quite a bit different than 360ohms. Is the coil really underdamped or am I missing something?

[Qiaozhi]

Does this include the damping resistor? I assume I have to connect this adjusting tool in series with the damping resistor, am I wrong?

No ... you need to remove the damping resistor first, as the tool replaces it during testing. After adjustment for critical damping, remove the tool and measure its resistance with a multimeter. Then fit the nearest standard value fixed resistor.

[gonsaIo]

Thanks a lot I will watch them and adjust it.

[surfdetector]

I already solved the problem. A trace of the mosfet was burnt. Now I'm adjusting the damping resistor. I have put a 10k pot in series with a 200R resistor, and a 2k resistor in parallel with both the pot and resistor (I read it from Qiaozhi in a thread). Does this include the damping resistor? I assume I have to connect this adjusting tool in series with the damping resistor, am I wrong?

You might find it of interest to watch these two videos that I did on the damping resistor jig and adjusting:

https://youtube.com/playlist?list=PLgBlcFVgN7pTXowPv747Rd5MniTrONUBI

[gonsaIo]

I already solved the problem. A trace of the mosfet was burnt. Now I'm adjusting the damping resistor. I have put a 10k pot in series with a 200R resistor, and a 2k resistor in parallel with both the pot and resistor (I read it from Qiaozhi in a thread). Does this include the damping resistor? I assume I have to connect this adjusting tool in series with the damping resistor, am I wrong?

[gonsaIo]

I don't know if it was the original problem, but it's quite possible: the IRF9530 pin trace connected to R2 and R3 I think (the left one from this point of view) doesn't work, it's burnt. What can I do, connect the mosfet pin directly to R2 and R3?

[gonsaIo]

OK, I'll do it as soon as possible. Thanks.

[waltr]

edit: I checked it again and it's in -4.3 V now... -5 and +5V power supply is working. Now there's no variation of voltage when placing a target near the coil, it's stuck at -4.3V

-4.3V output from an op-amp powered by +-5V means the output is at the 'rail' and can not go further.
Re-check all your soldering for bad connections and solder bridges, shorts. Use a 10x magnifier and good lighting to see possible issues.

[gonsaIo]

Well, by build goes from bad to worse... I wanted to check the U7 pin 1 value just to see if it was correct, just to check, and it results voltage was below 2.3 V (it was at 0,4V). I took out the threshold pot (47K) and shorted p1 of PL2 to p2 and tried to adjust R14... nothing changed, it was still in 0.4 V. I took out the PL2 pot and shorted p1 and p2, but it still showed 0.4 V. What can have happened?? I didn't touch anything since it was working before.
edit: I checked it again and it's in -4.3 V now... -5 and +5V power supply is working. Now there's no variation of voltage when placing a target near the coil, it's stuck at -4.3V

[Qiaozhi]

Step 7
You should set the voltage to (minus) 2.1 volts

That's what it used to say in the old Build Document. Have a look at post #1 in the part on updates and corrections:
2020-08-24: Build Document updated to match kit components, and also to correct an error concerning the adjustment of R14 (minimum sample delay).

The value of 2.3V is correct, as it used to say -2.1V.
Check your copy of the Build Document. It should be labelled Ref. 20200822-A (shown in the footer on each page).

[gonsaIo]

Step 7
You should set the voltage to (minus) 2.1 volts

I don't understand, I'm looking at the guide ( [Doc. Ref. 20200822-A]) and in Step 7 it says Set the DC voltage level to around 2.3V.