Voltage Divider

Two resistors share a supply voltage in proportion to their values. Measure the middle with a multimeter.

Beginner
Analog Electronics
5 parts

Opens in your browser with the parts, wiring and code already in place. Press Run to watch it work, then change anything you like.

How it works

A 9 volt supply feeds two resistors in a row: R1 of 1 kilohm, then R2 of 2 kilohms, then back to ground. The same current has to flow through both, and the voltage divides between them in proportion to their values, so R2, being two thirds of the total, takes two thirds of the 9 volts: 6 volts. The multimeter is wired from the point between the resistors to ground, so it reads exactly that.

This is the idea behind most analog sensors and volume controls. A potentiometer is a voltage divider whose split you move by hand, and a light or temperature sensor in a divider turns a changing resistance into a changing voltage a microcontroller can read. A multimeter in volts mode is a very large resistance, so it hardly disturbs what it measures. There is no sketch here, because nothing in the circuit needs code.

Parts

DC Supply
2 × Resistor
GND
Multimeter

Wiring

DC Supply + → Resistor 1 A
Resistor 1 B → Resistor 2 A
Resistor 2 B → GND
DC Supply - → GND
Multimeter V/Ω → Resistor 1 B
Multimeter COM → GND

Arduino code

// Voltage Divider
// Press Run, then read the multimeter: it shows the voltage across R2.
// There is no sketch to write: this is a circuit, so there is nothing for code to do.
void setup() {
}

void loop() {
}

Try changing it

Select R2 and change its resistance to 1000. The two resistors are equal now, so the multimeter reads half the supply, 4.5 volts.
Select the supply and change its voltage. The reading changes by the same proportion, because the divider ratio stays the same.
Select the multimeter and switch its mode to current, then see why a meter in the wrong mode changes the circuit it is measuring.
Point at a pin or a wire while it runs: a card shows its voltage and current (9 volts at the top, 6 in the middle, 3 milliamps through both). Then switch the view above to Schematic to see the same circuit as a diagram, and save it as a SPICE netlist.

Open this circuit and run it

Next challenge

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