SAADC very high noise.

RE: SAADC very high noise.

Luk3 — Mon, 03 Jul 2017 12:22:14 GMT

I read it yesterday but I had a hope that I it's something missing in the configuration. I used to lower noise in embedded ADC, but it is good to hear that is normal. Thank you.

RE: SAADC very high noise.

Jørgen Holmefjord — Mon, 03 Jul 2017 11:32:06 GMT

Your results seems to be within what is expected. Please see this thread.

RE: SAADC very high noise.

Luk3 — Mon, 03 Jul 2017 06:16:15 GMT

Without oversampling:

/* Configure ADC */
memset(&saadc_config, 0 , sizeof(saadc_config));
saadc_config.interrupt_priority = 7;
saadc_config.low_power_mode = true;
saadc_config.oversample = NRF_SAADC_OVERSAMPLE_DISABLED;
saadc_config.resolution = NRF_SAADC_RESOLUTION_14BIT;

/* Configure channel */
memset(&saadc_channel_1, 0 , sizeof(saadc_channel_1));
saadc_channel_1.acq_time 	= NRF_SAADC_ACQTIME_3US;
saadc_channel_1.burst 		= NRF_SAADC_BURST_ENABLED;
saadc_channel_1.gain		= NRF_SAADC_GAIN1_5;
saadc_channel_1.mode		= NRF_SAADC_MODE_SINGLE_ENDED;
saadc_channel_1.pin_p		= NRF_SAADC_INPUT_VDD;
saadc_channel_1.pin_n		= NRF_SAADC_INPUT_DISABLED;
saadc_channel_1.reference	 = NRF_SAADC_REFERENCE_VDD4;
saadc_channel_1.resistor_n	= NRF_SAADC_RESISTOR_DISABLED;
saadc_channel_1.resistor_p  = NRF_SAADC_RESISTOR_DISABLED;

RE: SAADC very high noise.

Jørgen Holmefjord — Fri, 30 Jun 2017 14:38:51 GMT

Could you post all your SAADC and channel configurations?

RE: SAADC very high noise.

Luk3 — Fri, 30 Jun 2017 11:45:19 GMT

I tried measure the coin battery voltage with the internal reference and nothing changes.

RE: SAADC very high noise.

Jørgen Holmefjord — Fri, 30 Jun 2017 11:41:27 GMT

Yes, the internal refrence should be stable, but if you sample VDD you might not get stable readings if VDD is not stable.

RE: SAADC very high noise.

Luk3 — Fri, 30 Jun 2017 11:16:38 GMT

Only with the multimeter. Even with slightly unstable VDD, I think the internal 0,6V reference voltage should be stable.

RE: SAADC very high noise.

Jørgen Holmefjord — Fri, 30 Jun 2017 10:51:33 GMT

The noise does seem a bit high, have you checked that VDD is stable using other measurement option? Also have a look at this thread about accuracy of the SAADC.

RE: SAADC very high noise.

Luk3 — Fri, 30 Jun 2017 06:01:42 GMT

SD in enabled but an advertising isn't. With the internal reference and gain 1/6 results are very similar. I also tried to measure a 3V coin battery, no difference. Supplying board with battery instead of USB without effects. I checked schematic and between regulator and nRF52 is diode placed. Schotky diode Vf varies from load, can it be source of that noise?

RE: SAADC very high noise.

Turbo J — Thu, 29 Jun 2017 14:09:29 GMT

Try again with the internal reference and 1/6 gain. But VDD may be noisy due to chip activity like CPU or radio.