ADC negative voltage

[janik]

Hello,

I've already read a lot in the forum, but I'm not quite sure yet.
Is it possible to measure an AC voltage with the ADC? Normally no, but in the documentation a resistor ladder is mentioned which should allow the measurement of positive and negative voltage.
Can I use it to measure an AC voltage that oscillates around 0?

Or can I measure either positive or negative voltage, depending on how the register is set?

[hmolesworth]

Yes, turn on both 160k bias resistors and AC couple the AC signal with a capacitor. Peak-Peak voltage must be within the VDD, typically 3 volts max

//                        +----------------------------------------------+
//                        |                 nRF52840                     |
//                        |    VDD                                       |
//                        |   --#--                                      |
//                        |     |                                        |
//                        |     |   Option                               |
//                        |     +-|   160k                               |
//                        |       |<- High                               |
//                        |     +-|   Bias                               |
//             ||C        |     |                                        |
//     +-------||---------O-----#------------#------#--> P0.nn SAADC     |
//     |       ||         |     |   Option   |      |    Ref = Int       |
//     |                  |     +-|   160k  +++     |                    |
//     |                  |       |<- Low   | |   -----                  |
//     @                  |     +-|   Bias  | |   -----                  |
//     @                  |     |           +++     | 2.5pF              |
//     @  AC              |     |            |1M0   |                    |
//     @                  |   =====        =====  =====                  |
//     | Pk-Pk < 3 volts  |    ===          ===    ===                   |
//     |                  |     =            =      =                    |
//     |                  |                                              |
//     +------------------0-----+                                        |
//                        |     |                                        |
//                        |   =====                                      |
//                        |    ===                                       |
//                        |     =                                        |
//                        +----------------------------------------------+