Drive 12 LEDs with one I/O line

摘要

Several Design Ideas expand the I/O of a pin-limited microcontroller (references 1 through 4). The circuit in this Design Idea uses an alternative method (Figure 1). It limits external additional parts to one IC, and it drives as many as 12 LEDs in dot-bar or bar-graph mode. You can use the same technique in a dot-bar design (Figure 2). If you need a seven-rnsegment LED display, you can use the circuit in Figure 3, which shows how to rearrange the circuit according to a classic multiplexed, four-digit common-cathode display.