Circuits / Getting started
Button with a pull-down resistor
Released, R1 holds the output at ground (LED off); pressed, S1 takes it to the supply (LED on)
Tap a part to see its voltages and currents. It is a model, not a measurement.
What do you need?
- Push buttonSearch on Amazon
- Resistor 10 kΩSearch on Amazon
- Resistor 330 ΩSearch on Amazon
- Green LEDSearch on Amazon
- Jumper wires × 2Search on Amazon
- BreadboardSearch on Amazon
What does a pull-down resistor do?
A pull-down resistor holds a point at ground until something pulls it up. Here R1 (10 kΩ) ties the output to ground and the button S1 connects it to 5 V. Released, the output sits at 0 V and the green LED stays off. Without R1, the output would be floating: not connected to anything, it could read high or low depending on noise or even a nearby hand. Pressed, S1 takes the output to the supply and the LED lights through R2 (330 Ω) at about 8.9 mA. Meanwhile R1 lets 0.5 mA pass to ground, the small cost of holding the line down. The logic is the opposite of a pull-up: pressed reads HIGH, released reads LOW. The UNO's chip only has internal pull-ups (an ESP32 has both), so on an Arduino a pull-down like this one is an external resistor.
Values from the Protoboard ISO simulation: a model, not a bench measurement.
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