Answer 7
The circuit shown here addresses all of the remaining issues. The switches ground the resistor network at various points, creating voltages for the A/D input as shown.

The topmost closed switch controls the voltage seen by the ADC; any switches closed below it have no effect. When no buttons are pressed, the input goes to 5 V.

Unfortunately, when using just one resistor value in the network, the voltage steps are not equal. This presents a problem when extending the concept for more switches.

Contributor: Dave Tweed

Published May 2003