Sensors
How electronics feel heat, see light and measure the weather.
The question
How does a weather station know the temperature, the wind speed and how much rain has fallen?
What you’ll discover: how sensors turn the real world into electrical signals, and the sensors inside a real weather station.
In simple terms
BeginnerTurning the world into electricity
A sensor changes something in the real world (light, heat, motion, moisture) into an electrical signal: a change in resistance, voltage or current that a circuit can measure.
| Sensor | Senses | How it signals |
|---|---|---|
| Light-dependent resistor (LDR) | Light | Resistance falls as light increases |
| Thermistor | Temperature | Resistance changes with temperature |
| Reed switch | A nearby magnet | Contacts close |
| Tilt switch | Tilting | Contacts close when tipped |
| PIR (passive infrared) sensor | Body heat moving | Output switches on |
| Humidity sensor | Moisture in the air | Usually a capacitance change, read by a small chip |
Sensors in a real weather station
Our own West Lethbridge weather station is a Davis Vantage Pro2, and it’s a good example of sensors at work:
- Temperature and humidity: electronic sensors inside a white, louvred radiation shield that keeps the sun from heating them directly.
- Wind speed: spinning cups, called an anemometer. Each turn produces pulses, and the station measures how fast they arrive.
- Wind direction: a vane that turns a potentiometer (Lesson 7), so its resistance tells the station which way the vane points.
- Rain: a tipping-bucket collector. Each time a tiny bucket fills, it tips and a magnet passes a reed switch, sending one pulse for a fixed amount of rain: 0.2 mm on the metric version.
Go deeper
IntermediateReading a sensor with a voltage divider
Resistive sensors like LDRs and thermistors are usually read with a voltage divider (Lesson 7): the sensor and a fixed resistor in series across the supply. As the sensor’s resistance changes, so does the voltage at the middle. A transistor can switch on it, as in the night light, or a microcontroller can measure it (Stage 4).
Choose the fixed resistor close to the sensor’s resistance in the middle of the range you care about. That gives the biggest change in voltage for a given change in light or temperature.
AdvancedAccuracy, calibration and non-linearity
Sensors are rarely perfect. An NTC thermistor’s resistance changes with temperature along a curve, not a straight line, so converting it to degrees takes a formula (such as the Steinhart–Hart equation) or a lookup table. Every sensor also has an accuracy specification, and it may drift over time.
Calibration means comparing a sensor with a trusted reference and correcting for the difference. Placement matters as much as the electronics: a perfect thermometer in direct sun or beside a warm wall still gives the wrong air temperature. That’s why weather stations use radiation shields and follow placement guidelines.
Quick check
What does a sensor do?
It turns something in the real world (light, heat, motion) into an electrical signal a circuit can measure.
How does a tipping-bucket rain gauge report rain?
Each time its small bucket fills and tips, a magnet passes a reed switch and sends one pulse, worth a fixed amount of rain.
Why is a weather station’s temperature sensor kept inside a white louvred shield?
To keep sunshine from heating the sensor directly, so it measures the air temperature.
Words to know
- Sensor
- A device that turns a physical quantity into an electrical signal.
- Thermistor
- A resistor whose value changes with temperature.
- Anemometer
- An instrument that measures wind speed.
- Calibration
- Comparing a sensor with a trusted reference and correcting it.
Learn more
- West Lethbridge Weather: see the station’s sensors reporting live
- Build: Automatic Night Light
- Next: Motors and buzzers
Electronics School is part of the Discovery Zone. Every activity here runs on small batteries or a USB cable: never wall outlets. The one plug-in tool is the optional soldering iron, set up by an adult.