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STM32 PCB ADC Voltage Measurement Problem

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Raiser

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Hello,

I am using a custom built PCB having two STM32 microcontrollers. There are four motors around the PCB, each of them drawing 4-5A current.

I am trying to measure battery voltage on the PCB using one of the ADC channels of the microcontroller. I calibrated the ADC values with voltmeter and a power supply by changing the voltage on the ADC input pin. The voltage is measured from a voltage divider circuit connected to the battery (resistors are selected for 3.3V). The problem is; I am getting correct voltage measurements from ADC when the motors is not running. However, if I turn the motors on, I am getting incorrect voltage measurements, with an error about 0.7 volts.

I think that the problem is related to analog GND, cable lengths and magnetic noise.

Any suggestions and solutions about this problem?

Any helps will be appreciated.

Regards,
Mert
 

Raiser

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The reference is zero volts, AGND is connected to ground.
 

Raiser

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The STM32 A2D must have a finite reference voltage.
Sorry, I misunderstood.

AVCC is connected to 3.3volts. For the chip I am using (STM32F103RB), there is no analog reference input pin. Also, I could not found any register containing internal reference voltage setting.
 

klystron

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It is a good idea to use an external voltage reference. Using the supply 3.3 VDC as a reference expose the analogue measurements to all the PSU noise.
 
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    Raiser

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Raiser

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Thank you, klystron. I will try it.
 

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