The figure below illustrates the key elements of a temperature measurement system employing a MC68HC11 microcontroller.
The temperature sensor provides a voltage proportional to the temperature; an example of such a sensor is LM25 (a temperature sensor that can be used with an analogue to digital converter like ADC0804 to give a digital output suitable for a microprocessor).
The output from the temperature sensor is connected to an ADC input line of the microcontroller. The microcontroller is programmed to convert the temperature into a binary-coded decimal (BCD) output which can be used to switch on elements of a two-digit, seven-element display. But, since the temperature may be fluctuating it is essential to use a storage register which can hold data (temporarily) long enough for the display to be read. The storage register, such as 74HCT273, is an octal D-type flip-flop which is reset on the next positive-going edge of the clock input from the microcontroller.
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