Figure 1 Low-current sensor.
Resistor R can assume values between 1 and 10 k ?, depending on the transistor. See in this section to determine which blocks described in Chapter 3 can be added to this block to control high-power loads. The contact conditioner capacitor must assume values between 0.05 and 1 ?F, depending on the application.
In the same block, we see how can the load be replaced with a resistor (1kΩ) to produce a signal for an external circuit. If a BC548 is used in this circuit, resistor R must be a 10 kΩ component and C a 0.047 ?F capacitor. Powering the circuit with 5 to 12 V, the circuit can be used to drive TTL or CMOS inputs from mechanical contact sensors. The output of this circuit goes to the low logic level (0) when the sensor is closed.
