nrf51822 ACD pins

[Aaron]

I am trying to figure how to pin my nrf51822 on a PCB. I need the chip to sample and convert an analog voltage signal coming from a photodiode heartbeat detection circuit. I have read through the documentation quite a bit and I believe I understand most of this, but I'm not getting a clear picture as to whether or not I need to do anything with AREF0/AREF1. I am still building the sensor, so I can adjust my gain accordingly. I think the easiest method would be for me to use the VREF_VBG of 1.2V. If I design my sensor to have a low impedance and ensure that my sensors output voltage is < 1.2V, can I simply connect the output of the sensor to any pin in the range 4-10? Do I need to connect anything to AREF0 and AREF1? Can they be left hanging? Also, I expect this only ranges positive voltages, correct? I'll need to offset my sensor by (Vsensor,max/2)?

[Mahesh Venkitachalam]

My understanding is that you need to use AREF0/1 only if your input voltage range and the ADC voltage range is not matching.

Have you looked at the nRF51 Series Reference Manual? (Not the product spec.)

There are 5 pages of information on the ADC in the above and it talks about all the issues you mentioned above.

If you are looking for a simple ADC example, here's my project that uses ADC to read light levels from an LDR:

electronut.in/.../

Regards

[Stefan Birnir Sverrisson]

There are also ADC examples available on Nordic's Github.

Yes, the ADC only ranges positive voltages.

As stated in the nRF51 Series Reference Manual v3.0, table 311, you can measure different voltage range on the input with adjusting the prescaling of the ADC. with e.g. 1/3 prescaling and VBG reference you have range 0V - 3.6V on the input.