Skill Level: Intermediate-Advanced
Duration: 2 hours
Explore the properties of the Wheatstone Bridge using our pre-soldered Sensor board. Build projects that could one day link to the Internet of Things (iOT).
Build a circuit that senses a change in a sensor while exploring the properties of this fundamental circuit, the Wheatstone Bridge. This board measures small changes in resistance (temperature, pressure, light, and humidity). Use Sensor to create interactive games that control LEDs when there are changes in pressure or temperature.
What does this circuit look like?
The Wheatstone bridge circuit has been used for over 150 years to identify unknown resistance or measure a change in resistance. Often, Resistors R1 and R3 are known values (often identical), Rx is unknown and R2 is a form of a variable resistor that can be changed until Vb is zero.
Resistance based sensors are commonly used as low cost means of measuring pressure, temperature, light, humidity, water quality and water quality.
In the Sensor board circuit, R2 is a potentiometer that is used to balance the circuit. The Sensor also uses a Operational Amplifier (OpAmp) to amplify the change in voltage when the circuit is unbalanced. Because of the sensitivity of the circuit, it is near impossible for Vb to be exactly zero (which would be indicated by both LEDs being off.)
How does Sensor work?
Turn R2 to the point where a fraction of a turn flips between the two lights. In this mode, if LED1 is left on, when the resistance Rx becomes higher than R2 (i.e. it gets darker), the circuit flips and turns on LED. Conversely, if LED2 is left on and the resistance of Rx becomes lower than R2, LED1 will turn on.
Adjust potentiometer to find the point where a fraction of a turn changes the lights. If you want to measure an increase in resistance (darker) leave LED1 on. If you want to measure a decrease (lighter), leave LED2 on.
Sensor is also available as a soldering kit.