Telling them apart

Seven levels, six lines

BTNS can sit at seven levels: all of 3V3, a half, a third, a quarter, a fifth, a sixth, and 0. A sketch reads it and has to say which. The simple way is to draw a line halfway between each pair of neighbours; a reading above a line and below the one over it is that button.

In millivolts, with 3V3 on the header, the six lines are:

The sketches carry exactly this list, highest first, and stop at the first line the reading is above:

const int LIMIT_MV[] = {2475, 1375, 963, 743, 605, 275};

Millivolts, so one list fits every board

An Uno counts against 5 V, a Pico against 3.3 V, and an ESP32 against a reference of its own. A count means something different on each, so the sketches convert to millivolts first. On an ESP32 and an ESP32-S3, analogReadMilliVolts does it with calibration stored in the chip; on an Uno and a Pico the count is scaled by the ADC's full scale, 5000 mV or 3300 mV. Then one list of lines works everywhere.

The ESP32's ADC reads nothing below about 0.1 V and tops out near 3.1 V at the Arduino core's default setting. Neither end matters here: the lowest button, U6, is at 0.55 V, and U11's full 3.3 V reads as the top of the scale, far above its line at 2475 mV.

How much room there is

The tightest pair is U8 and U6, a fifth and a sixth of 3.3 V: 0.66 V and 0.55 V, 0.11 V apart. Their line is halfway, so a reading can wander about 55 mV either way before it is misread. In counts that is roughly:

Ordinary noise on a breadboard is a few counts, so both are comfortable. What eats the margin is a wrong supply: 5V on the header's 3V3 pin raises every level by half and puts most of them over the wrong line.