Vintage 555 - A general-purpose button debouncer

RE: Vintage 555 - A general-purpose button debouncer

shabaz — Mon, 14 Aug 2017 16:07:45 GMT

Great post! Very cool thread to share various debouncing methods.

I recently needed to implement single and double-press (and in the future perhaps triple-press) so it was fun creating the state machines for that while also debouncing. One project I semi-worked on used a button for multiple purposes, the user could swap it out for a control unit which would send something like 1-Wire signals. So then the system needed to understand button-presses (and debounce that) but also recognise when the button was swapped out and the human replaced with a higher-speed machine for different functionality (kind-of like a headset which might have a simple mute button, but the more advanced version will have a display and soft-buttons). I didn't do the hardware or software for that portion of the design.

Another technique where the debounce is semi-hardware and semi-software, is to use a I2C expander and an interrupt. Then, whenever the interrupt signals a pin change, the signal levels are read using I2C. Since it takes some time to perform the I2C read action, the software performs a partial debounce by confirming the data has not changed (the data from the last I2C read is always retained to be compared) or by then waiting for the next interrupt (when the button is released) if an action on release is desired. Some expanders have some deliberate built-in debounce capability too, I've not tried them.

RE: Vintage 555 - A general-purpose button debouncer

Workshopshed — Mon, 14 Aug 2017 13:36:21 GMT

More debouncing

Switch Debouncing - The Lab Book Pages

Follow the debouncing flip-flops | EDN

RE: Vintage 555 - A general-purpose button debouncer

dougw — Sun, 13 Aug 2017 16:06:43 GMT

Great topic - good job on the blog.

Good way to use up those 555s.

A couple of additional points:

As Michael points out, if the switch is connected to an arduino, it can be debounced with software - no extra components or wiring.
If you need perfect and instantaneous debouncing you can use two switches (one for set and one for reset) or a double throw switch also performing set and reset - my favourite is to connect a SPDT switch to cross-coupled inverters or NAND gates.

RE: Vintage 555 - A general-purpose button debouncer

koudelad — Sun, 13 Aug 2017 06:53:57 GMT

Nice post [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4b749376-8970-4f03-a8e3-432dca7749c2/contentimage_5F00_1.png:16:16]

I have seen the RC variant on STM32 Nucleo boards and I guess it is the cheapest if we consider the total bill of material.

By the way, PSoCs have a component just for this purpose: a Debouncer. Works like a charm.

RE: Vintage 555 - A general-purpose button debouncer

jw0752 — Sun, 13 Aug 2017 05:07:58 GMT

Hi Enrico,

Thanks for this post. It will be very useful for anyone with a switch that needs debouncing. I love the production of your videos, always so professional. I always think of you and smile when I cobble my videos together.

John

RE: Vintage 555 - A general-purpose button debouncer

Workshopshed — Sat, 12 Aug 2017 18:11:52 GMT

Thoughts on using a Schmitt Trigger for debounce?

RE: Vintage 555 - A general-purpose button debouncer

DAB — Sat, 12 Aug 2017 16:56:27 GMT

Excellent post.

The venerable 555 should be in the IC hall of fame. So simple, and yet so versatile.

DAB