Skip to the schematic
DT ClassroomDesign and Technology studios
CircuitLab · Electronic systems

Choose the right part. Then prove it works.

Work out the resistor for an LED, set the switching point of a light or temperature sensor, size the base resistor for a transistor driver and estimate how long a battery will last. Every answer comes from the real equations, rounded to values you can buy.

Circuit

Download

Design sheet

These are teaching models of typical parts: a 10 kΩ NTC thermistor, an LDR of about 20 kΩ at 10 lux, a BC547, BC337 and TIP120. Check the datasheet of the part you actually buy. Resistor values are from the E12 series.