| | | Bend Sensor® Variable Deflection Threshold Relay Switch: This circuit is a derivative ofthe simple Bend Sensor® Variable Deflection Threshold Switch of Figure 1.5 on the previous page. It has use where the element to be switched requires higher current, like automotive and industrial control relays. The Bend Sensor® device is arranged in a voltage dividerwith RM. An op-amp, U1, is used as a comparator. The output of U1 is either high or low. The non-inverting input ofthe op-amp sees the output of the divider, which is a voltage that increases with deflection. At zero deflection, the output ofthe op-amp will be low. When the voltage at the non-inverting input ofthe op-amp exceeds the voltage ofthe inverting input, the output ofthe op-amp will toggle high. The triggering voltage, and therefore the deflection threshold, is set at the inverting input by the pot R1. The transistor Q1 is chosen to match the required current specification for the relay. Any medium power NPN transistor should suffice. The threshold adjustment pot, R1, can be replaced by two fixed value resistors in a voltage divider configuration. The diode D1 is included to prevent flyback, which could harm the relay and the circuitry. | | |