Reading Force sensing resistors values via ADC of nrf52DK

[vam5104]

Hi,

I need to make two FSRS to read and display the output simultaneously. So, initially I had to get the ADC values from two analog pins at the same time. After struggling a bit, I was able to get it. Now, I need to get the force readings from FSRS. The vDD was taken as 5V since I connnected both the FSRs to the same 5V pin in the nrf52 dk. R_DIV was taken as 2500 ohms. However, the readings I obtained were not accurate. This is because, the ADC values show values fluctuating between 0,1,-1,2. It’s very confusing for me.

Can anyone help me with this?

Thanks!

[AmbystomaLabs]

It is erroneous to say you are taking a reading on two inputs simultaneously. nRF52 has but a single ADC that is muxed on multiple pins. The two pin samples are always separated by one sample interval.

You should probably post a schematic of what you are doing and your code.

In addition, care should be taken if you are using 5vdc as your divider reference. You cannot take a gpio pin above nRF_Vdd.

Also you should read up on how an SAADC works. The input forms an RC network during acquisition which can give bad data depending on the equivalent source resistance and capacitance.