#318 555Timer/Bistable
Using the 555 timer as a bistable latch (debouncer).
Notes
Ben Eater’s 8-bit computer yields more interesting circuits. Here I’m reproducing his bistable latch circuit based on the 555 timer.
How it Works
This circuit takes advantage of the fact that the trigger and reset pins provide direct access to the SR latch within the 555 timer that drives the output.
- The trigger pin provides a SET input when it rises above the 33% division of the 5V input - 1.67V.
- The reset pin provides an inverted (Active low) RESET input.
With pull-ups on both trigger and reset pins, the 555 is in a SET (output high) state.
A make-before-break single-pole double-throw switch is wired up to switch between grounding either the trigger and reset pin. This will toggle between SET and RESET, with debouncing since multiple pulses will effectively be ignored by the latch.
Performance
The switch throw is effectively debouned - and despite using it rudely, I haven’t been able to reproduce any bouncing input signals yet.
However when zoomed in very tightly on a rising edge, there is not a very clean swing. This appears to be cross-over distortion on the 555 output.
Construction
