Are momentary SPDT footswitches as reliable as SPST?

Started by Processaurus, May 13, 2022, 02:04:45 AM

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Processaurus

I'm confused by software debounce of momentary switches. There is a nice, easy hardware way to debounce SPDT momentary switches with a NAND latch circuit.  They used it in classic arcade game controls, and it switches instantly and cleanly, and reliably.

I'm wondering if anyone has long term experience or opinions on the X-wing type SPDT momentary stomp switches,

vs the more common SPST type with the rounder actuator.

The latching X-wing switches were notably less reliable than the 3pdt blues, back in the day.

They kind of have a different feel, it is like a click, rather than a smoosh.

There's also some 3PDT blue momentary switches I've never used, anybody use those for their digital circuits?  If you did, would you just use one pole, or parallel all 3? Would parallel add redundancy?

anotherjim

Latching will have extra mechanical parts that wear.
Momentary can have a short life if the user doesn't get an immediate response to operating it - human nature will try pressing harder! The classic of this is the power button on a TV remote because I've never met a TV that doesn't wait for a short while before apparently obeying this command, so the user tries squishing and jabbing the button harder causing wear of the bubble contact within.
Parallel spare contacts if wish, if it's a PCB mount, you might as well but if it's wired, I wouldn't bother. Unused spares give the repair tech an easy fix!

Processaurus

I guess with the parallel thing, you get redundancy if one of the poles fails open.  Reliability would be worse if they fail short though. I couldn't find any info on which failure mode is more likely...

It's hard to find rated cycles or datasheets on the switches.  Only one I could find was for Eswitch's red momentary 3PDT, at 30,000 cycles, which is identical to the latching 3PDT blues.  One of the X-wing momentary switches had 50,000 cycles. Not the half a million cycles like you see from microswitches or 1 million cycles from Lehle's $20 mushroom cap footswitches, or 20 million for mechanical keyboard switches (similar to the type Boss uses).  I saw the fancy $15  SPDT's at Love My Switches are rated at 200,000 cycles.  Debatable whether a typical stompbox will see that many cycles, but it is an indicator of quality, and we've all had crummy footswitches crap out on us.


anotherjim

A short circuit is an unusual failure mode for us but in heavy-duty/safety-critical work contact welding is a worry - so they use contact pairs in series and/or switch both feed & return paths.
I guess we can call our stuff "mission-critical" and it can ruin a song when a signature sound isn't available.


stallik

Given that all poles switch every time the button is pressed, I'm not sure you could describe unused poles as spare. They've had as many switches as the others.
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein

anotherjim

True Kevin, although if one contact should decide to become a non-contact, Sods law dictates it will be the one you are relying on. But then, if you do hardwire spares in parallel you won't know about it until they all fail.
Not switches, but relays, the industry I worked in always designed in some spare contacts and we had a process allowing us to temporarily use them if we had a working contact fail, although it was always prefered to change the relay.


Fancy Lime

I'm wondering if anyone has used mechanical keyboard switches in a "normal" diy enclosure. Maybe activated with a rubber flap of aome kind like the old DOD or EXAR pedals.

Andy
My dry, sweaty foot had become the source of one of the most disturbing cases of chemical-based crime within my home country.

A cider a day keeps the lobster away, bucko!

Processaurus

Quote from: Fancy Lime on May 15, 2022, 12:43:16 AM
I'm wondering if anyone has used mechanical keyboard switches in a "normal" diy enclosure. Maybe activated with a rubber flap of aome kind like the old DOD or EXAR pedals.

Andy

Small Bear sold the metal actuator part of the classic stomp switch that would press on a tact switch mounted on your PCB, gently, with a spring. Line 6 used them for their DL4's and that series of 4 button pedals. People did complain about the switches failing, I would replace them with better quality Omron tact switches and I hadn't heard of failures after that. Not sure why the original switches would fail, tact switches are known for very long life cycles, and the spring actuator was pretty gentle.

Some arcade buttons are just a chunky plastic actuator for a microswitch. To use a Cherry MX mechanical keyboard switch you'd need some kind of actuator that would protect it from taking more than a couple ounces of force.