Voltage Divider

$V_{out} = V_{in} \frac{R_2}{R_1 + R_2}$

Example: 5 V with $R_1 = R_2 = 10$ kΩ gives 2.5 V.

Uses: scaling a 12 V signal down to a 3.3 V ADC input, setting a reference voltage, reading a potentiometer or an LDR.

Caution: the formula assumes no load current. A load resistance in parallel with $R_2$ lowers $V_{out}$ — keep the load at least 10× larger than $R_2$, or buffer the output with an op-amp. A divider is not a power supply: never use one to power a circuit.