High Current Draw on Target Device

Hi,

I am using your 2 of ADCPis to perform some Voltage readings on a target device. However, I have noticed when observing the current drawn by the target device that almost a milliAmp is drawn when 10 ADC connections are being made to the target from the ADCPi. I have physically unplugged the wires from the ADCPi to the target to prove this is the case. The Pi and ADCPi are being run off a completely different Power Supply to the target, with a common Ground connected. Is there any setting I can use to disconnect the ADC inputs from the ADC when not in use to avoid any extra current draw on the target?

The extra current draw on the target is acceptable while the measurements are ongoing but I need to be able to turn them off to measure the true current draw of the target in various states. The current draw of the target is expected to be in the order of uA so the extra mA really throws this off as even using a calculated offset I lose a lot of resolution.

Thanks!

Hi

The ADC Pi uses a resistor voltage divider on the inputs to increase the voltage range from 2.048V to 5V. The voltage divider has a 10K and 6.8K resistor so each input will have a 16.8K connection to ground which would be a 0.06mA current draw at 1V input.

There is no way to disable the voltage dividers through the software interface so you would need to put a physical switch between your target device and the ADC input to disconnect it. You could also use an op-amp to buffer the voltage between the target and the ADC. Op-amps have a high impedance on their inputs so they would have less impact on your current draw measurements.