Israel Schleicher

The circuit in Figure 1 is similar in principle to that of a previous Design Idea (Reference 1) but offers improved, more reproducible performance. The output current is almost constant over an input-voltage range of 1.2 to 1.5 V and is insensitive to...

In most keypads, pressing a key closes a contact that bridges two lines in an xy matrix. If you use a microcontroller to detect a key closure, checking the states of (x+y) lines requires an equal number of I/O pins. Occupying only one free I/O pin, the circuit Figure 1...