Analog Front End - fhdm-dev/scoppy Wiki

Examples

Some analog front end designs

Measuring different voltage ranges

To measure different voltage ranges (eg. -5V to +5V or 0V to 0.1V etc) than the default (0-3.3V) you will need to add additional circuitry in front of the Pico to attenuate/amplify the signal and/or provide an appropriate voltage offset so that the voltage at the ADC pins of the Pico is between 0 and VREF (by default VREF is 3.3V).

If you decide to add an analog front-end, the Scoppy app needs to be configured so that it will display the correct voltage. You do this by tapping on the Channel badge at the bottom of the screen, tap Settings and then Voltage ranges. You can enter up to 4 voltage ranges per channel. Your front-end indicates the currently selected voltage range via GPIOs 2 & 3 for Channel 1 and GPIOs 4 & 5 for Channel 2. The logic levels at these pins and the corresponding voltage range id is shown in the tables below. By default these pins are pulled down to LOW so if you do nothing then voltage range 0 is selected.

GPIO 2 GPIO 3 Ch 1 Voltage Range
LOW LOW 0
LOW HIGH 1
HIGH LOW 2
HIGH HIGH 3
GPIO 4 GPIO 5 Ch 2 Voltage Range
LOW LOW 0
LOW HIGH 1
HIGH LOW 2
HIGH HIGH 3

Please note these are the pin assignements for version 4 and higher of the firmware. Please upgrade if you are using older firmware.