Up to now we have considered inputs as being digital in operation i.e. the input is either a 0 or 1. But suppose we wish to make temperature measurements, but not just hot or cold (1 or 0). We may for example require to:
(a) Sound a buzzer if the temperature drops below freezing.
(b) Turn a heater on if the temperature is below 18°C.
(c) Turn on a fan if the temperature goes above 25°C.
(d) Turn on an alarm if the temperature goes above 30°C.
We could of course have separate digital inputs, coming from comparator circuits for each setting. But a better solution is to use 1 input connected to an analogue to digital converter and measure the temperature with that.
Figure 11.1 shows a basic circuit for measuring ...