- Published: Tuesday, 21 May 2013
- Written by Jon Chandler
- Hits: 4837
This is a repost from EDN Magazine's Design Ideas.
This Design Idea shows how a single microcontroller port can drive a lot of output lines through shift register. In this case we use the shift register with strobe control to achieve perfect output line control.
Shift register outputs can drive LEDs, relays, etc. In other words, they can be used as (additional) general purpose outputs.
Today there are shift registers that have DATA and CLOCK inputs only, like 74HC164, and shift registers with same inputs plus STROBE control input, like 74HC4094 or 74HC595. The shift registers without STROBE control have short-term transient states at outputs during shifting. Transients occur because shift register is directly connected to output lines. This kind of shift register can be used for driving LEDs and similar devices where short-term transient is irrelevant. For example, the human eye can't notice LED flickers shorter than 10 msec. The shift registers with STROBE control have two registers.