Battery voltage too high in QGC

[arachnida]

Hello,
I'm a newbie here, but not new to all sorts of multirotors like OP, MK, DJI, MWii and others.

I've got a rev 2 board from a friend and connected it to a PSU 12V output. The reading in the QGC is way too high, 14.6V. I've checked the resistor R4 on the board and it reads around 8.4K (on board measurement). The log voltage7 reading gives me 1.99V. But here I'm a bit confused, the wiki reads:

VIN 7 Voltage read from R3, R4 voltage divider. Rev1 board (4.7k): LOG_VOLTAGE6 / .221 = Vin; Rev2 board (8.45k): LOG_VOLTAGE6 / .136 = Vin;

Do I have to use LOG_Voltage6 or 7? I guess 7 is correct, but the calculation in the WIKI is done on 6?!?

If I calculate the reading and divide by 0.136 for a rev2 board I get 14.63V, also what I see in the QGC.

What am I doing wrong?

Cheers,
arachnida

[Max]

Hi arachnida, welcome to the forums!

Thanks for the heads-up on the typo in the docs -- fixed. I'm not sure about your voltage readings though... sorry! Hopefully someone else will chime in.

-Max

[arachnida]

Thanks Max for correcting the WIKI!

I guess the easiest way is to change the calculation in the FW, but I don't want to recompile every new release of the AQ FW. Changing the voltage divider Rs is also an option, but maybe there is a much more logical explanation.

Still waiting for my Hoverthings Flip frame to arrive so I can test out this promising board.
/arachnida

[Kisssys]

Hello arachnida

Have you actually read the voltage of that power supply, I'll bet it's putting out about 14.63 volts.

If I applied 14.63 volts to the voltage divider of 8.45k and 1.33k it would give me 1.99 volts the AQ says it is. You don't have a problem, you have a pretty good voltmeter.

Cheers
Steve

[arachnida]

Hi Steve,

Yes i'm positive it's 12.0 V. My PSU has a V and A meter and I double checked with a multimeter. BTW, I'm using the latest beta but also tried the r37v2 to no avail.

I will do some more tests tomorrow to see if the voltage divider is giving the correct voltage to the ADC.

Have a good night,
arachnida

[Kisssys]

The only thing it could be is the value of R3 is not correct. It should be 1.33k. One side should be grounded and the other should read 1.99 volts and 14.63 volts on the other side of R4. I believe I helped somebody a while back that R3 was missing completely now that I think about it.

[arachnida]

I took my Rigol Scope to see the signal on the V divider, it reads a clean 1.64V DC that can be expected for a 12V power supply. (1.64V/0.136=12V) So the input to the ADC is correct but log_voltage7 reads 1.98V (noise from 1.988 - 1.990) and the QGC shows 14.6V. The calculation in the FW is fine but is done on a wrong reading from the ADC.

If I lower my PSU I see the voltage in the QGC dropping accordingly.

[JussiH]

Well, it sounds like there could be some error on your board or an ADC malfunction on the MCU. Pls measure voltage on pin18 on the MCU to see if it corresponds with the output of the voltage divider.

[arachnida]

Thanks Jussi, that is exactly the info I needed! I will test it tomorrow and report the result.

[arachnida]

Pin 18 measures 1.64V, exactly the same as the output of the V div.