Variable Resistors

Photoresistors

Photoresistors can detect changes in light. When the light on the sensor increases, the resistance decreases. If you have ever had a night light that turned on when you shut the lights off, you have probably seen a photoresistor in action. These could be used in a robot to turn on lights when you enter a dark area.

Thermistor

Thermistors detect changes in temperature. As the temperature being measured increases, the resistance decreases. These can be seen in everything from soldering irons, 3D printers, and coffee makers. Basically anything where you want to automate the measurement of heating or cooling something to a specific temperature, you would use a thermistor.

Magneto resistor

Magneto resistors detect changes in the magnetic fields of their environment. As you apply a stronger magnetic field, the resistance increases. These sensors are commonly used in electronic compasses in order to determine magnetic North. It is also important to remember if you are using one of these, try and keep it away from as much metal and anything that would emit electromagnetic interference (like motors) to ensure it is reading accurately.

Humistor

Humistors detect humidity, which is the amount of water molecules in the air. These sensors can be very important when you are operating a robot that expects a dry environment and needs to alert the user if the humidity rises too much. It is also sometimes used in bathroom sensors to activate a fan or exhaust system to decrease the humidity.

Force Sensitive Resistor

Force sensitive resistors (also referred to as a pressure sensor) react to an outside force applied to them. As the force increases, the resistance decreases. One important application of these types of sensors is being able to understand the grasp of a robot and the pressure it is exerting. Imagine trying to make a robot that could handle an egg and you want to make sure that the pressure applied isn’t too much to break the egg.