calibrate voltage / wrong voltage

[konwin]

Hello,
I successfully flashed my old original DSO150 with STM32F103CB.
The only thing I observed is that the measured voltage is around 25% to low. The test signal is shown as 2.5V and an AA battery I checked with my multimeter at 1.18V is shown at 0.9V.
Is this adjustable? Or have I done the calibration wrong (connect probe clamp to the ground clamp and leave connected while pressing ok and switching to AC/DC as stated)?

[mean00]

Hi
The problem is depending on your hw revision, the internal gain/ resistors are different, so it will always be wrong on some hw.
The "basic calibration" only calibrates the zero, i.e. dc offset. So if you see zero when you ground the signal, you did it correctly.

On my todolist i have the "advanced" calibration to calibrate YOUR device properly.
I did that in the past, it works fine, but the code is missing at the moment.

Short term, i can suggest either :
1- If you can, change capture/dso_adc_gain.cpp. it contains the gain for the different stages.
2- I can blindly change it, but i dont know your hw, might be better , might be worse.

BTW, the main goal of the "advanced" calibration was to be much more accurate.
In the past, when it's done, the value are not bad at all.

[mean00]

The explanation is here :
http://goingbacktoelectronic.blogspot.com/2019/02/dso150-input-gain.html

[mean00]

I'm manually splitting the voltage range issue into Issue #9
#9

[mean00]

@konwin
There is now in master a 5v calibration method to lower the error due to internal Vref variation
It is assumed to be 1.2 but i've measured it up to be up to 10% wrong
One calibrated, the absolute error goes down A LOT.