Reading 250V on the HV bus

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3 weeks 7 hours ago - 3 weeks 4 hours ago #11627 by thecardella
Hello,
I'm going through the build videos of the Arduino UNO all in one clock. So far I had to stop at the end of the HV circuit build because I am getting a read of 250V on the HV pin where I would expect 195V.
The 5V bus looks good, I get a stable 5.02V, the Arduino is on and the IRF840 gets very very hot, too hot to touch.
I am powering the board from the board connector (not the Arduino one) with a 12V power supply.

Has this happened to anyone else? Any idea?
Thanks

Alberto
Last edit: 3 weeks 4 hours ago by thecardella.

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2 weeks 6 days ago #11635 by Ty_Eeberfest
It sounds to me like there is an issue with the voltage feedback in the HV generator circuit. I'm talking about the signal that's called HVS on the schematic. It goes to A0 on the UNO.

With the circuit running check the voltage on A0 (referenced to ground).

If you read 0v then there's probably a problem with the connection between UNO and clock, or maybe a cut trace in the clock board. Use schematic and eyes to physically check the condition of the trace.

If you read greater than 0V but less then 2V you need to look at resistors R1 and R2 and make absolutely sure they are the right values in the right places. I'm thinking you will find your resistors are swapped.

If you read 2V +/- 0.2V then I'm not sure what's going on. Check back and we'll go from there...

Look into it later when the dust is clearing off the crater.

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2 weeks 6 days ago #11636 by thecardella
Hi, thanks for the suggestion. I get 2.91V on the pin A0.
I also checked continuity between each part following the schematics but I could not find anything wrong or missing connection (so far).
I guess that having ~3V on HVS means that the voltage divider is correct so R1 and R2 are in the correct place, right?

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2 weeks 6 days ago #11637 by thecardella
I thought I replied but I cannot see the post so excuse me if I'm writing a duplicate (I'm not sure if the forum has a delay in display posts or I did not press Submit)

Thanks for the suggestion! I have gone through all the tracks checking for expected continuity and comparing with the schematics. I could not see anything unexpected.
On pin A0 of the Arduino I am reading 2.91V...so I guess the voltage divider is setup correctly (I mean R1 and R2) ?

On a side note, I am using a clone Arduino board, actually it's a combination of ATMega328 and ESP8266, with the Arduino UNO format, so I would not expect surprises on that side, but maybe you have record of past issues with a simular board that I'm not aware of.

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2 weeks 6 days ago #11638 by Ty_Eeberfest
Your posts go into the moderation queue and sit there until somebody here releases them. That's because you are new. You will not be moderated after you make a few more posts. It's a pain in the ass but it's the only way to positively keep the porn spammers away.

Okay so... you're correct the voltage divider sounds like it's put together correctly and doing its job. The ~3 volts corresponds nicely with the excessively high voltage. The voltage is running away to the high side because somehow the software isn't seeing the feedback form the divider so it thinks it needs to drive harder to bring the voltage up. Eventually it "winds up" to a high limit.

At least that's one probable scenario. I'm a little suspicious of your "hybrid" arduino since I've never tried the software on one like it. If you have a regular UNO - clone or legit - please try loading up the code on it and doing a test run to see if anything changes.

Another thought is that at the stage of the build that you are on, the HV generator is running uncalibrated. That can certainly result in the HV reading a bit high but what you are reading seems absurdly high. In order to calibrate the HV generator you'd need to continue with the build to the point of having all the anode and cathode drive circuitry complete, i.e. get it to the point you can light up a tube. Install 1 tube and connect up a button to CONN_FRONT. Do a factory reset by while holding the button down while powering up. Release the button. The tube should soon start counting 0 - 9 repeatedly. Tap the button while the tube is displaying "8". That should start the calibration routine. When it finishes calibration, cycle power again but don't touch the button. Read your HV voltage. If it's 170 - 180 you're good. Just be sure to repeat the whole factory reset and calibration ritual when you have all 6 tubes connected.

Let me know what happens. This is a bit weird. Usually when this happens it's just user error putting in the divider resistors.

Look into it later when the dust is clearing off the crater.

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2 weeks 6 days ago #11639 by Ty_Eeberfest
Also... just remembered this. Ages ago there were issues with the metal case of the USB connector on some UNO clones touching the clock board, shorting things out and causing all sorts of random hell. I think changes to the clock board layout to compensate for UNO variants eliminated this. But take a look just to be sure nothing on the UNO is touching where it shouldn't be.

Look into it later when the dust is clearing off the crater.

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