DIY tactile footswitch

[armdnrdy]

I've been working out a project for a small box Dimension C with a few mods.
The Dim C has stereo outputs which are switched using a SIL5 BA623 flip flop IC that controls JFETs in three locations.
I usually rip out JFET switching just like the next guy but....I wanted to keep this in a small enclosure so...I decided to leave it as is.

I now needed a SP momentary footswitch.
I have a few of the "soft touch" footswitches laying around but, I wondered how these would work with the flip flop. These switches would be more prone to bounce than a tactile switch such as what Boss uses in their switching circuits.

I remembered that Steve (Small Bear) sells switch actuators, and I recall seeing something about their use with tactile switches. I looked on Small Bear's site...the actuators were out of stock.

A few weeks back I picked up a "broken" A/DA Flanger for a good price off of ebay. The only thing wrong with it was a broken footswitch. I still had the actuator piece so...I took a look at what I could do with it.

I figured that a piece of PC board would fit nicely between the actuator frame. The four "ears" that hold the actuator to the switch body could be folded over to secure the circuit board.
I pulled out a tactile switch that I had and took some measurements. It looked like it might work!

I pulled up Eagle..made a simple board. Two wire pads, the tact switch pads, and two traces connecting the two....done.

I etched and drilled the board, solder the tact switch onto the board...and assembled it.

It worked! 

I opened and enlarged the spring inside of the actuator so that it would fit over the tact switch, resting on the board. When assembled, the tact switch actually fits inside the shaft of the footswitch. There is a plastic "rod" inside of the foot switch shaft that needed to be cut down a bit. That shaft is what makes contact with the tact switch button.

That was all there was to it! Simplistic DIY at it's finest! 

Here is an image of the board file:


Here are some pictures of the finished product, the tact switch, and a similar switch type that can be used.


Here is a PDF of the board for etching.
https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Tact%20stompswitch%20board%20print.pdf

[deadastronaut]

nifty bit of diy there man...

[armdnrdy]

Thanks Rob.

This is one of those "necessity is the mother of invention" things! 

[R.G.]

Very nice.

It replicates almost exactly the footswitch modules that Truetone (formerly Visual Sound, just changed the name) uses in all their current pedals. Another of those cases of convergent evolution.

This setup works very well, and is very reliable. The only quirk is that the spring length has to be right - and you found that out too.

Good work.

[Perrow]

1590Aers dream

[JerS]

Nicely done! Thanks for sharing all the pics. The visual really helps to understand what you have done here.

[armdnrdy]

Thanks guys.

The foot print is 14mm X 24.4mm. (The wire pad side of the board could be made 2.5mm smaller)

The measurement from the top of the nut to the bottom of the PCB is only 6.5mm!

Very miniscule behind enclosure depth!

[duck_arse]

that looks fantastic and odd at the same time, and so much smaller than the barrel type pushbutton I once used.

[armdnrdy]

that looks fantastic and odd at the same time, and so much smaller than the barrel type pushbutton I once used.

Looking at the finished product....it does indeed look like something is missing!
Hey...where's the rest of the switch? 
It's an illusion caused by the tactile switch being hidden inside of the actuator shaft.

[Beo]

This is awesome. I just took apart a latching footswitch I had lying around, and it looks like the latching mechanism is separate from the spring actuator and isn't needed. So it doesn't have to be a momentary switch to juryrig it into this design.

Does your modified spring make direct contact with the tactile switch, or do you have something in between the spring and the button?

[armdnrdy]

Hey Travis,


Yes, you can use either type of footswitch...momentary or latching.
You just need the actuator, spring, and the plastic rod.

I opened the large end of the spring (the end protruding out of the footswitch shaft) with a pair of needle nose, so that the spring end would fit over the tactile switch, resting on the circuit board.

The end of the plastic rod is what actuates the tactile switch button. The rod needs to be cut a bit.
Start with about 1/8", press the circuit board onto the actuator frame, holding it in place, check the travel in the footswitch. If you want more travel...cut a bit more off of the rod.
If you cut too much off...the rod will no longer make contact with the tactile switch button.
I ended up with about 2mm of travel. (From when the footswitch is pressed...to where the tactile switch is engaged)

[Beo]

I see. Mine has a metal cone center rod which could be filed down I guess.

[armdnrdy]

I saw images of footswitches disassembled online, and noticed that some switches have a metal rod.

That shouldn't be a problem...same thing applies. You have to make it shorter.
As you stated, filing would be the correct approach.

[duck_arse]

or you could use a tact switch with a longer shaft. the variations available in tactile switch specs is enormous.

[armdnrdy]

Yep...that would work as well.

Here's a 6mm X 6mm SPST, N.O. tact switch with a 17mm actuator.

http://www.mouser.com/ProductDetail/E-Switch/TL1105LF160Q/?qs=sGAEpiMZZMsgGjVA3toVBIOx%252bqVkqfBWOY9BQ%252b9WkLo%3d

[armdnrdy]

I found some images on the net of a switch disassembled. They should provide a better visual of what the spring and rod look like.

[MrBinns]

Yhy not just debounce the mom switch? You can also buy mom tactile switches, not just soft touch.

Very cool though. I enjoy seeing post like this.

[armdnrdy]

Yhy not just debounce the mom switch? You can also buy mom tactile switches, not just soft touch.

The tactile switches used in this DIY are momentary.

I didn't want to go the route of de-bouncing because, it has been my experience if you want true, fool proof de-bouncing, it often requires a schmitt trigger and other components.

See figure 3:
http://www.eng.utah.edu/~cs5780/debouncing.pdf

I didn't want to add any components to the already packed DC-2 board so...I figured I'd go with a momentary tactile like the original.

[MrBinns]

o ok. That's the guide I used to debounce my switches.

[armdnrdy]

Update:

Today I received some SIL op amps and the BA634 SIL5 T flip flop ICs for the upcoming DC-2 build.

I made a SIL to DIL adapter board to test the op amps, and I bread boarded the front end of the DC-2 switching circuit to test the flip flops.

I used the DIY tactile switch for the testing. Everything went without a hitch! All components tested good!

On a whim...I changed out the tactile switch for a standard SP, momentary soft touch switch.
This switch failed miserably with the Boss flip flop circuit!
It was completely inconsistent, sometimes not turning on or off when actuated.
As I had suspected, this switch would need major de-bouncing to work with this circuit.
This got me thinking...I might revisit other circuits I have tested to see if the replacement of the standard switch with the DIY tactile will allow me to lower the parts count by deleting a majority of the de-bouncing components.

Here is the test circuit:



Here is an image of the failing momentary soft touch switch: