Properties of an Electronic Sensor
- An electronic sensor is made up of:
- A sensing device (LDR, thermistor, strain gauge)
- A circuit that provides an output registered as a voltage
- Devices which perform an “input” function are called sensors since they ‘sense’ a change in the physical environment ie. light and convert these into an electrical signal
- These can be either:
- Analogue sensors (produce a continuous output voltage)
- Digital sensors (produce a binary, non-continuous output voltage)
Potential Divider Circuits with Sensory Resistors and Strain Gauges
- Strain gauges and sensory resistors are used in potential divider circuits to vary the output voltage
- This could cause an external component to switch on or off depending on its surroundings eg. a garden light switching on automatically after sunset
- Recall that the resistance of an LDR varies with light intensity
- The higher the light intensity, the lower the resistance and vice versa
- The resistance of a thermistor varies with temperature
- The hotter the thermistor, the lower the resistance and vice versa
- The resistance of a metal-wire strain gauge varies with extension
- The longer the extension, the higher the resistance
- Compression of the strain gauge lowers the resistance
- From Ohm’s law (V = IR), the potential difference Vout from a resistor in a potential divider circuit is proportional to its resistance
- If an LDR, thermistor, or strain gauge’s resistance decreases, the potential difference through it also decreases
- If an LDR, thermistor, or strain gauge’s resistance increases, the potential difference through it also increases
