RE: nRF52832 with Thermistor Sensor - ADC

Steve H — Fri, 10 Mar 2017 08:45:03 GMT

Thanks, Sigurd.

RE: nRF52832 with Thermistor Sensor - ADC

Sigurd — Thu, 09 Mar 2017 21:30:23 GMT

Hi Steve, here is an updated link.

RE: nRF52832 with Thermistor Sensor - ADC

Steve H — Thu, 09 Mar 2017 11:33:22 GMT

Hi Ole, just noticed that your link in 5 is broken.

RE: nRF52832 with Thermistor Sensor - ADC

Mark — Fri, 17 Jun 2016 00:53:28 GMT

Thanks Ole

RE: nRF52832 with Thermistor Sensor - ADC

Ole Bauck — Wed, 15 Jun 2016 15:22:01 GMT

Hi,

Between 3.3V regulator and Vdd there is a diode, see here. So a voltage around 3V is normal.
If you use 1/6 gain and 10 bit resolution the usable range will be 810. You can also use 1/5 gain to increase the range (saturating voltage will be 3V) and higher resolution (12-bit or even 14-bit with oversampling). You can change the resolution by changing SAADC_CONFIG_RESOLUTION in nrf_drv_config.h to e.g. SAADC_RESOLUTION_VAL_12bit.
You don’t need to use PPI, you can trigger a sample in code with nrf_drv_saadc_sample().
I am a bit unsure if using internal pull-up resistor on the GPIO would work, but in your case I would not do it anyhow because the accuracy of the internal pull-up resistor is bad (11k-16k), see here. The ladder resistor in SAADC (which is configured with the .resistor_p = NRF_SAADC_RESISTOR_PULLUP) is about 160kohm, see here. Not sure what the accuracy is on this resistor.

You can set down the acquisition time to 3 us, which is just within what we recommend with source resistance of 10kohm, see here. Do that with:

nrf_saadc_channel_config_t channel_config =
    NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);
channel_config.acq_time = SAADC_CH_CONFIG_TACQ_3us;