This block can be used with LDRs to trigger a circuit when light falls on the sensor. It can also use NTCs to trigger the circuit when the temperature rises or, with a pressure sensor, to close a relay when the sensor is pressed.
The basic block is shown in Figure 1. In the figure, we show a simple circuit driving a 50 mA (or less) relay and the blocks that can be triggered by this circuit.
The potentiometer is used to adjust the sensitivity of the circuit. The correct value of the potentiometer must be chosen as function of the resistance of the sensor under normal applications. The recommendation is the use of a potentiometer 3 to 5 times lower than the resistance of the sensor. Sensor with resistances below 1 kΩ are not recommended for this circuit.
