### Author Topic: Did you ever make a touch-plate?  (Read 568 times)

#### Mark Hammer

##### Did you ever make a touch-plate?
« on: March 17, 2021, 04:40:47 PM »
I watched a Youtube from the synth diy guy earlier today ( https://www.youtube.com/watch?v=DT6nZsixP0M ) and thought I'd try my hand at it.  I had accidentally bought some copper-clad board that was simply too thin to be of use making project boards, so this struck me as a good alternative use of it.  I drafted an image I thought might be suitable and etched several.  The principle is simple.  You provide a number of proximal interleaved contact points, and the resistance of your finger bridges them, providing a resistance that varies with how much pressure one applies and how many points of contact your finger provides.  Needless to say, and as so many polygraph tests have amply demonstrated, a person's "galvanic skin response" ( https://en.wikipedia.org/wiki/Electrodermal_activity ) is not exactly constant, so the resistance achieved is not especially predictable.

Needless to say, though, resistance CAN be varied by pressure.  And if one uses the touchplate in conjunction with a high-value resistor (e.g., 4M7 or 10M) to form a virtual voltage divider, with the touch plate forming either the ground leg or the input leg, one can use the touch-plate like a pot.

Here's mine.  I took a wild shot at the number of contact points and other physical parameters to use.  The contact surface measures about 2-3/4 x 1-1/16.  Depending on the moisture in my fingers (and I've had to wash my hands at least 20 times today so they've become rather non-conductive at the moment), I've been able to get the touchplate resistance as low as 10k.

Since the off resistance is infinite, one could use it as an expression control for something that uses the Line 6 standard (0-10k) by putting a fixed resistor in parallel with it.  The ones I made are thin enough that you could attach one to the surface of a guitar with tape and have a finger expression controller.  I had tried this previously with a photocell, but the caveat there is that one needs a decent light source that can be blocked with a finger or hand in order to use the photocell.  A touchplate could be used in any lighting conditions.  And hey, if stage lighting makes you sweaty, it works even better!  Just note that it is not instantly responsive...but it does respond.

#### 11-90-an

##### Re: Did you ever make a touch-plate?
« Reply #1 on: March 17, 2021, 08:49:55 PM »
hear me out...

use that as a foot controlled expression pedal, just have to take off your shoes and socks...
flip flop flip flop flip

#### iainpunk

##### Re: Did you ever make a touch-plate?
« Reply #2 on: March 18, 2021, 09:40:37 AM »
hear me out...

use that as a foot controlled expression pedal, just have to take off your shoes and socks...
leave on the socks, on stage, the sweat makes them conductive!

cheers
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『ｓｎａｉｌｐｉｌｌｅｄ』

#### duck_arse

##### Re: Did you ever make a touch-plate?
« Reply #3 on: March 18, 2021, 09:59:25 AM »
hey Mark - if you have that shown pitch tracks under the heal of your palm, and then divided the other section, as to be under the thumb fingers, and you halved the track width and spacing in one block, and then halved again in the second block ....... sensitivity? log finger response?

nah, I don't know what I'm talking about.
.... adding a bit of "supplementary hair" ....

#### iainpunk

##### Re: Did you ever make a touch-plate?
« Reply #4 on: March 18, 2021, 10:50:39 AM »
i can confirm that an idiot wah kinda works, i made the touch pad with aluminium foil, old library card and pritt stick.
it works, it does the wah thing, but the noise floor is unbearable... so i took it off of the breadboard to be replaced by my new overdrive project

cheers
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『ｓｎａｉｌｐｉｌｌｅｄ』

#### Mark Hammer

##### Re: Did you ever make a touch-plate?
« Reply #5 on: March 18, 2021, 10:56:01 AM »
hey Mark - if you have that shown pitch tracks under the heal of your palm, and then divided the other section, as to be under the thumb fingers, and you halved the track width and spacing in one block, and then halved again in the second block ....... sensitivity? log finger response?

nah, I don't know what I'm talking about.
If skin conductivity was constant, you MIGHT be making sense.  But it's probably easier to achieve constancy and reliability with an optical cloud-detector!

#### bean

##### Re: Did you ever make a touch-plate?
« Reply #6 on: March 18, 2021, 12:54:56 PM »
I've etched a couple similar to what you posted Mark and was able to produce a bit of effect with it.

Also, these have a much denser concentration than one can get with etching:
https://smallbear-electronics.mybigcommerce.com/alpha-membrane-force-sensor-mf-01/
https://smallbear-electronics.mybigcommerce.com/alpha-membrane-force-sensors-mf-02/

I used the MF02 with an adhesive mount on a small enclosure, then wired it to a jack for a bit of plug and play.

#### antonis

##### Re: Did you ever make a touch-plate?
« Reply #7 on: March 18, 2021, 06:35:07 PM »
Left one for Depth and right one for Rate in a tremolo, perhaps..??
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

#### garcho

##### Re: Did you ever make a touch-plate?
« Reply #8 on: March 19, 2021, 10:43:01 AM »
I love my Microfreak, the keyboard is awesome, can very expressive:

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#### Mark Hammer

##### Re: Did you ever make a touch-plate?
« Reply #9 on: March 19, 2021, 01:49:52 PM »
I have been VERY tempted to get one.  Somebody was selling one 2nd hand locally for \$300Cdn.

#### KarenColumbo

##### Re: Did you ever make a touch-plate?
« Reply #10 on: March 19, 2021, 02:25:17 PM »
I want such a touchpad on my keyboard rig! Gotta translate its output to MIDI somehow, though. And that's where my poor brain disconnects.
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#### garcho

##### Re: Did you ever make a touch-plate?
« Reply #11 on: March 19, 2021, 02:40:39 PM »
Quote from: Mark Hammer
I have been VERY tempted to get one

Go for it! They're a little cheaper than the Music Easel

The pros outweigh the cons, IMO, a great little machine with a TON of modulation possibilities and a great digital synth engine. I'm a fan of used gear but I bought it full price new, and am so glad I did, no regrets. There was even a hidden mic input for a future vocoder which is now included in the firmware. I use one of these for the mic:

I like the idea of having these little touch plates on a guitar with active electronics. Good for an experimental guitar with built in effects or MIDI or something like that. If there was a strip right under the high E string you wouldn't have to move your plucking hand out of the active zone to use it. It might not be as effortlessly expressive as having the tremolo vibrato bar in your hand while you pluck, but it would still be way cool, and using it wouldn't be very disruptive.

Quote from: KarenColumbo
I want such a touchpad on my keyboard rig! Gotta translate its output to MIDI somehow, though.

That's what a µC is for, could do it with a \$5 arduino nano clone, very easily. The tricky part would be to incorporate it into a MIDI signal, you'd need a MIDI "merge" device or have to incorporate it into whatever MIDI controller you want to use with your set up and build the whole thing. Otherwise it would hog the entire MIDI port. I tend to have different controllers for different devices, I don't like too much multi-channel MIDI because I use a lot of sequencers and samplers that need separate MIDI systems so they don't respond to global commands and all start or stop at the same time. Basically what I'm saying is you should totally build your own MIDI controller and have touch strips on it!
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