[SOLVED] Is it posible to measre the AVref Reference Voltage through Software in Stm32

I need to measure the 3.3V input given to my ADC input pin. but the reference to AVref is varying from 3.28 to 3.33 because of this my error also increasing, and if i am calibrating at the time the Voltage is 3.28 but after some time its varying to 3.31... so is it any possibility for measuring what the voltage is given to my ADC reference.

Thanks,

Hi,

I assume you are using VCC as reference voltage.
Because of the known problems with drifting VCC this is not recommended for absolute voltage measurement with reasonable precision.
There is a good reason why they spent a pin as reference voltage input.
--> Connect a reliable, precise and stable voltage reference IC to it.

Measurement means "compare with a reference".
If you want to measure your reference voltage this means you need to "compare" it with a another - more reliable - reference.
Do you have such a reference? If yes, then why do you use VCC as ADC_reference?
--> If your reference is not reliable then it is no reference.

Some microcontrollers have a built in voltage reference. If your microcontroler has one, then use this reference instead of VCC - always.

Klaus

There are trick. You need to measure well known voltage with ADC. You may use ion or just a diode with forward drop. But having this value, you can calculate the supply voltage with same precise as you getting input voltage. I did this trick when mcu directly supplied from battery.

Many STM32 have an internal reference voltage that can be used to calibrate supply relative ADC measurements. The method is described in the reference manual ADC section. If no internal reference is present or it's not accurate enough, you can connect an external precision reference to an ADC input and use it for the correction.

Hi,

What's the benefit of using VCC as VRef when there is the internal VRef?
I see no benefit in:
* accuracy
* precision
* effective resolution
* processing speed
* software effort
...
Klaus

Hi ,

Thanks for your valuable reply.

My hardware team is given the VDDA with 3.3V the same as VDD and they are not cared about the error, but i am not satisfied with the result. so i am possible to find the error on my own so that i can obtain a best result by reducing the error.

Easyrider83

There are trick. You need to measure well known voltage with ADC. You may use ion or just a diode with forward drop. But having this value, you can calculate the supply voltage with same precise as you getting input voltage. I did this trick when mcu directly supplied from battery.

i will try this thanks for this info

FvM

Many STM32 have an internal reference voltage that can be used to calibrate supply relative ADC measurements. The method is described in the reference manual ADC section. If no internal reference is present or it's not accurate enough, you can connect an external precision reference to an ADC input and use it for the correction.

I will try this too

Hi,

My hardware team is given the VDDA with 3.3V the same as VDD and they are not cared about the error, but i am not satisfied with the result.

Click to expand...

The problem is not with pins VDDA and VDD.
It´s the problem of
* the pin VREF (or whatever it is called with your microcontroller)
* and your software setup for ADC reference voltage selection.

Klaus

Btw: You could give additional informations like:
* exact microcontroller type
* schematic
* code

Its stm32f100c8

- - - Updated - - -

Hi guys the problem is solved. there is a Vrefint in my ADC register where i can read the Voltage and found the error. Thanks for all for your kind support.