RE: nrf51822 ADC always reads 0.6v

_Scott_ — Tue, 12 Jul 2022 18:02:48 GMT

Not sure why it took so long to figure this out, but turns out AIN0 and AIN1 on the nrf51 DK cannot be used since they are tied to the 32kHz oscillator. AIN0 is what I was trying to use. This was exacerbated by having a broken signal generator which made it appear like AIN2-7 were having the same issue. After switching to AIN2 and connecting a functioning source, the ADC works as expected.

RE: nrf51822 ADC always reads 0.6v

_Scott_ — Mon, 11 Jul 2022 23:10:42 GMT

devzone.nordicsemi.com/.../7317.ADC_5F00_Config.pdf

So reading through this documentation, Figure 1 and the paragraph above it reveals the ADC has an internal power supply of 0.6v. It would appear what I am stuck reading is the internal power supply voltage. The ADC configuration will cause R^ain to vary by table 1. The signal generator I am using to output a dc signal has 50ohm output impedance. Accounting for 50ohms and R^ain in a voltage divider calculation, I should still not be seeing 0.6v as the Analog in value. However since I have tried every ADC configuration option, it would seem my issue stems from a circuit layout, however I am not sure how connecting a low impedance source to analog in would cause issues. The documentation linked specifically notes using less than 1kohm input impedence under the ADC Input Impedance Limitations section.