Differential analogRead

[jsartori]

Is there a way to do a differential analogRead on the Photon and/or Electron? Reading the posts I could find on it, it seems that there may not be; however, people mentioned some kind of dual mode that is similar. Can someone explain how to do this?

[ScruffR]

I guess you have seen this post

Faster ADC sampling challenges (SPI, MCP3008)

I added photonAudio sample 4. I should stress that this is a proof-of-concept only and only sort of works. The main thing is that the code uses two ADCs (ADC1 and ADC2). They’re run in dual-simultaneous mode, so both are sampled at the same time. They’re also run in scan mode so multiple pins are sample sequentially, and very rapidly, 5 cycles of the ADC clock (30 MHz). ADC1 is set to read A0, A2, and A4. ADC2 is set to read A1, A3, and A5. 44100 times per second, controlled by a hardware …

Can you elaborate what you'd need beyond that approach?

[rickkas7]

The STM32 hardware does not support differential ADC mode. However, you can use dual simultaneous mode to read a pair of ADCs at exactly the same time and difference them in software. Both signals need to be in the range of 0 to 3.3V relative to a common ground, not truly differential, however.

Rather than mess with using the ADC hardware at that low of a level I’d use an I2C differential ADC which is really designed for that purpose.

[Rftop]

@rickkas7

Rather than mess with using the ADC hardware at that low of a level I’d use an I2C differential ADC which is really designed for that purpose.

Adding to Rickkas7's suggestion : I believe the ADS1115 is a common choice. It is a 4-channel ADC, It requires 2 channels (+/-) for each 16-bit Differential Measurement, so you can measure 2 different voltage sources. There is a lot of sample code floating around and can be found for ~$8 USD.

[jsartori]

The code in the github linked in this post explores a lot of ADC features, which adds a lot of complexity. I just want to use one component of this – the dual sampling mode. Can someone show me how to use the dual sampling mode without all the other things this code is doing?