Building Systems That Work
Sensors & Signals
13 minStudent plan
How a sensor turns the physical world into a voltage, what the ADC does with it, and how to clean up a noisy reading.
After this lesson you can
- Say what any sensor is actually producing
- Work out the resolution of an ADC
- Choose between filtering and responding quickly
From the world to a voltage
A sensor converts some physical quantity into an electrical one. A thermistor changes resistance with temperature; an LDR changes resistance with light; a microphone converts pressure into voltage.
Most of them change resistance rather than producing a voltage, and a microcontroller cannot read resistance directly. So you put the sensor in a potential divider with a fixed resistor: as the sensor's resistance changes, the voltage at the junction changes, and that voltage is what you measure.
Choosing the fixed resistor sets your sensitivity. Roughly matching it to the sensor's mid-range resistance gives the largest voltage swing across the range you care about, which is exactly the trade-off the ratio-and-proportion lesson set up.
In the full lesson
- From the world to a voltage
- The analogue-to-digital converter
- Noise and filtering
This lesson comes with the Student plan. The first module of Engineering Foundations is free.