the evoluent vertical mouse I use has a notorious short lifespan because the switches aren't debounced or aren't debounced for a long enough period after only a year or two of wear. i demonstrated on an arduino that additional debouncing logic could fix the issue transparently to the user but never went further than that.
How to Debounce a Contact (2014)
71–80 of 82 posts
Re: How to Debounce a Contact (2014)
#72Earlier quoted context omitted.
Just don't implement SR debouncer, OK? And don't use MC140* series chips, those don't work with 3.3V used by modern micros. And when he says: > Never run the cap directly to the input on a microprocessor, or to pretty much any I/O device. Few of these have any input hysteresis. that's not true today, most small MCU made in 2005 or later (such as AVR and STM8 series) have input hysteresis, so feel free to connect cap…
What's wrong with the SR latch debouncer?
It needs SPDT switch, and that rules out most of buttons.
And if you do end up choosing SPDT switch, then there are much simpler designs which have switch toggle between Vcc and GND, like Don Lancaster's debouncer [0]. That design is especially useful if you have many switches, as you can wire all VCCs and GNDs in parallel, and use 8-channel buffers to debounce multiple ones.
The SR latch schematics only makes sense if you are working with TTL logic (popular in 1970/1980) which did not nave a symmetric drive output pattern, and there is absolutely no reason to use it in 2000's.
[0] https://modwiggler.com/forum/viewtopic.php?p=275228&sid=52c0...
Re: How to Debounce a Contact (2014)
#73> But some environments are notoriously noisy. Many years ago I put a system using several Z80s and a PDP-11 in a steel mill. A motor the size of a house drawing thousands of amps drove the production line. It reversed direction every few seconds. The noise generated by that changeover coupled everywhere, and destroyed everything electronic unless carefully protected. We optocoupled all cabling simply to keep the smo…
My favorite noise story is from just a couple years ago. Our controller would run fine for hours or days and then reset for no apparent reason. Looking at the debug output, I could tell that it wasn't a watchdog or other internal reset (e.g., system panic) and there had been no user input. The debug log basically said that someone pushed the reset button, which clearly wasn't happening. The EE and I were standing aro…
Only time I’ve ever run into this was:
- an am radio station nearby coupling into a pbx
- when some genius thought it would be a good idea to run Ethernet down the elevator shaft, right next to the lines feeding its truck sized motor.
Re: How to Debounce a Contact (2014)
#74> But some environments are notoriously noisy. Many years ago I put a system using several Z80s and a PDP-11 in a steel mill. A motor the size of a house drawing thousands of amps drove the production line. It reversed direction every few seconds. The noise generated by that changeover coupled everywhere, and destroyed everything electronic unless carefully protected. We optocoupled all cabling simply to keep the smo…
>Many years ago I put a system using several Z80s and a PDP-11
many years ago I wired up my own design for an 8080 system, but i was a self taught beginner and not very good at stuff like a capacitive RC debounce circuit so I couldn't get my single-step-the-CPU button to work.
I was reading the spec sheet for the processor and I realized I could kluge it with signals. There was something like a "memory wait" pin, and another one called something like "halt", but one fired on the leading edge of the clock, and the other on the trailing edge, so I was able to use a SPDT push button and a flip flop to single step halt/memory wait on the first bounce, and then restart only on the first bounce when the button was released.
Re: How to Debounce a Contact (2014)
#75Earlier quoted context omitted.
What's wrong with the SR latch debouncer?
It needs SPDT switch, and that rules out most of buttons. And if you do end up choosing SPDT switch, then there are much simpler designs which have switch toggle between Vcc and GND, like Don Lancaster's debouncer [0]. That design is especially useful if you have many switches, as you can wire all VCCs and GNDs in parallel, and use 8-channel buffers to debounce multiple ones. The SR latch schematics only makes sense…
Ah, that is better. Thanks!
Re: How to Debounce a Contact (2014)
#76I've been given a lot of suggestions for debouncing switches over the years. I'm just doing hobby stuff, either I have an endstop switch for some CNC axis, or more recently, some simple press buttons to drive a decade counter or whatever. My goal for one project was just to have a bit counter that I could step up, down, reset, or set to an initial value, with no ICs (and no software debounce).
I got lots of different suggestions, none of which worked, until I found one that did: 1) switch is pulled high or low as needed 2) switch has capacitor to ground 3) switch signal goes through a schmitt trigger
I designed this into its own PCB which I had manufactured and soldered the SMD and through-hole and ICs to that, and treat it as its own standalone signal source. Once I did that, literally every obscure problem I was having disappeared and the downstream counter worked perfectly.
When you look at the various waveforms (I added a bunch of test points to the PCB to make this easy) the results of my PCB produces perfect square waves. I found it interesting how many suggested hardware solutions I had to try (simple RC filter did not work) and how many "experts" I had to ignore before I found a simple solution.
Re: How to Debounce a Contact (2014)
#77What's with the advice about interrupts and undebounced signals?
What does it mean that a flip-flop gets confused? What kind of undesired operation could that cause?
Because, quite honestly, if connecting directly means occasional transient failures, then having less hardware is a tempting tradeoff on small PCBs.
Re: How to Debounce a Contact (2014)
#78Earlier quoted context omitted.
>Plenty of embedded microcontrollers in the 70s Weren't those just PC computers and less microcontrollers?
No, though chips like the 80186 did blur the line. But what I mean is that different companies sold things like 8051s with BASIC in ROM. Parallax had a very popular product in this category based on a PIC, you've probably heard of it: the BASIC Stamp.
You were talking abut microcontrollers from the 1970s, then you bring up Parralax
as an example.
Re: How to Debounce a Contact (2014)
#79Earlier quoted context omitted.
No, though chips like the 80186 did blur the line. But what I mean is that different companies sold things like 8051s with BASIC in ROM. Parallax had a very popular product in this category based on a PIC, you've probably heard of it: the BASIC Stamp.
You were talking abut microcontrollers from the 1970s, then you bring up Parralax as an example.
No, that was your edit to my text. I said, "in the 70s and later". You removed the "and later". You are behaving badly.
Re: How to Debounce a Contact (2014)
#80> One vendor told me reliability simply isn't important as users will subconsciously hit the button again and again till the channel changes. Orthogonally to the point of this excellent article, I found it striking how this was probably true, once--and then TVs got smart enough that it took seconds to change channels, instead of milliseconds. And then it was no longer possible for input failures to be corrected subco…
I have thought about that for a while and I wonder if it has to do with how memory becomes bigger more than it becomes faster. For example, compared to 30 years ago, PCs have about 1000x times more RAM, but it is only about 100x faster with about 10x less latency. It is a general trend for all sorts of devices and types of storage. It means that for instance, storing an entire frame of video is nothing today, but in…
> I wonder if it has to do with how memory becomes bigger more than it becomes faster
No. It is the software. Just look at Windows: Windows 10 and 11 has a third of functionality of 7 being 10 times bigger. What 10 years ago needed a mouse click, it needs 3 today. Software must communicate with the mothership so that mothership can see which functions are not used and remove them, making the program useless. And security: it just got more layers. Which, most of the time are useless and easy to bypass.