Basic Circuit Eliminates Numeric Keypad Polling

摘要

Using eight digital inputs, this circuit simplifies decoding of the common membrane 4×4 keypad matrix and eliminates the traditional requirement of scanning rows or columns. Any X-Y switch matrix, which can be part of some apparatus, can be considered with this device. The design uses eight pre-biased transistors-four NPN and four PNR When depressing a given switch, two transistors will turn on via the current through their internal biasing networks, providing a unique signature code that can be recognized and decoded. The generated code, which will be unique for each key, is readable with a simple 8-bit input statement. By enabling a pin-change interrupt on all eight inputs, the keyboard decode program can be entirely interrupt-driven.