Eli5: How do electronics measure Temperature and Humidity?
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Usually by varying the amount of current flowing inside a circuit by using materials whose resistance changes based on heat and temperature.
Current (Amps) is the measurement of how fast electrons are moving inside an electrical circuit.
Resistance (Ohms) is the measurement of how much the flow of electrons is being resisted.
By using a device called a *thermistor* we can measure temperature. Thermistors are made of a material that becomes more/less electrically resistive based on its temperature. So, when it’s warmer, the thermistor might let more current through an electrical circuit than when it’s cold. Measuring the current in the circuit will allow you to also know the temperature.
By using a device called a *resistive hygrometer* we can do the same for humidity. These are devices that increase/decrease current flow based on humidity.
Temperature is usually measured by either a thermistor or a thermocouple.
Thermistors are just special resistors who’s resistance changes based on the temperature. The problem is there are many different types. Each type works on a narrow band of temperatures and they aren’t as accurate as thermocouples
Thermocouples are two different metals coupled next to each other. When you heat up the metal it causes the electrons to move around at different rates, the electrons move away from the heat at different rates based on what metal they’re made from creating two different metals with two different densities of free electrons. The difference in electrons creates a voltage that can be used to determine the temperature.
There are two different types of electronic hygrometers. Resistive ones are the more commonly used types and use either a salt or conductive polymer change their resistance based on the humidity in the air. The other more accurate type is a capacitive type that changes in capacitance. It works on the same principle that causes more static buildup in dryer conditions.
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