WisBlock RAK4631 + RAK13002 IO adaptor pin WB_A0 ADC voltage

WisBlock
1

Hi. Could you please let me know what is the max voltage that I can put on pin WB_A0 ADC on a RAK13002 attached to a RAK5005 WisBlock and RAK4630.

I have a CT that I want to wrap around a grid line to measure the (solar) export current. The CT is rated 120A/40mA 10 ohms. I also want to read the mains AV voltage (240v AC).

Any help would be gratefully appreciated. Thank you.

2

Hi John,

The max input voltage on the WB_AO depends on the setup of the ADC with analogReference(AR_INTERNAL_3_0);
Possible values are:

typedef enum _eAnalogReference
{
  AR_DEFAULT,
  AR_INTERNAL,          // 0.6V Ref * 6 = 0..3.6V
  AR_INTERNAL_3_0,      // 0.6V Ref * 5 = 0..3.0V
  AR_INTERNAL_2_4,      // 0.6V Ref * 4 = 0..2.4V
  AR_INTERNAL_1_8,      // 0.6V Ref * 3 = 0..1.8V
  AR_INTERNAL_1_2,      // 0.6V Ref * 2 = 0..1.6V
  AR_VDD4               // VDD/4 REF * 4 = 0..VDD
} eAnalogReference ;

Beside of that, the input voltage should never ever go higher than the supply voltage of the RAK4631, which is 3.3V.

Keep in mind that WB_A0 is connected to the battery over a resistor to measure the battery voltage and that you cannot use it to measure external voltages, unless you remove a resistor on the base board. It is recommended to use WB_A1 instead.