Recipe

Turn an ADC reading into a real-world value

Use when: firmware has a raw ADC code and needs a voltage, or the temperature, light level or battery voltage behind it

Goal: the quantity the sensor measures, with the arithmetic in the right order

Taught in How an ADC works

1. 1

   Note n and V_{ref} as the firmware sets them, and which step convention you are using.

   Example

   Uno R4 Minima at its default 10 bits; suppose a 5 V reference: step = 5/1024 \approx 4.88 mV.

   Why: the same code means different voltages at different settings.

2. 2

   Multiply the code by one step.

   Example

   Code 614: 614 \times 5/1024 \approx 3.00 V.

   Why: the code counts whole steps up from 0 V.

3. 3

   If a divider scaled the signal down, divide by its ratio k = R_2/(R_1 + R_2).

   Example

   A 1/3 divider: 3.00 / (1/3) = 9.0 V at the battery.

   Why: the ADC measured the divider's output, not the original voltage.

4. 4

   Use the datasheet's relation between volts and the quantity.

   Example

   A sensor at 10 mV per °C reading 0.90 V, with 0.75 V meaning 25 °C: 25 + (0.90 - 0.75)/0.010 = 40 °C.

   Why: the sensor's datasheet, not the ADC, defines what a voltage means.