ADC Resolution Scale

[stevostephenson]

Posted on May 02, 2015 at 15:29

Hi All,

I am using the ADC on the STM32F407VGE to detect water through an infrared sensor. I am getting a very small change between seeing the water and not. With the sensor clear there is 0.1 volts which reads around 130bits on the conversion and with water it is around 140bits which should be around 0.103 volts.If I cover the sensor over with my finger I get full range of 4095 which will be 3.3volts, so i know that it works.There is a possibility that the sensor is still receiving some light from the emitter through the water but I am still getting a change even though it is small.Is it possible to alter the resolution to be able to make the difference of the 0.1v to 0.103v larger on the ADC converted value?Is there a possibility to use a look up table to determine the resolution scale? #adc #stm32f4 #look-up-table

[raptorhal2]

Posted on May 02, 2015 at 18:52

In approximate increasing order of accuracy and complexity:

1. Oversample to filter noise. 2. Use a 16 bit SDADC on a STM32F37x. 3. Use an external amplifier with gain and DC bias. Use a 3.3V reference for the amplifier so it saturates at a safe voltage when your finger is in the path. 4. Use an external SDADC. 5. Use Hudson River water. (just kidding) By a lookup table, I presume you mean calibrating each bit transition. That can improve accuracy, but won't overcome the 12 bit resolution accuracy. Cheers, Hal