Analog Interfacing to Embedded Microprocessor Systems, 2nd Edition

Figure 2.17B shows how a single analog input can be used to read two switches.

When both switches are open, the analog input will read 5 V. When switch S1 is

closed, the analog input will read 3.9 V. When switch S2 is closed, the input will

read 3.4 V, and when both switches are closed, the input will read 2.9 V. Instead

of switches, you could also use this technique to read the state of open-collector or

open-drain digital signals.

Figure 2.17C shows how a thermistor or other variable-resistance sensor can

be combined with an output. The microcontroller pin is programmed as an

analog input to read the temperature. When the pin is programmed as an output ...