brendan mccloskey

I'm afraid i'm still losing sleep over this one:

When one presses on a resistive touchpanel, there is a minute ramp up to the 'exact' or real XY location value; this is mainly due to the mechanics of this type of sensor implementation, but also caused in some part by a function i have implemented to simply detect touch: when the device is 'dormant', the sensors are forced back to ground, giving me a zero. Nice. And in Processing I've got a little averaging array. But the ramping-up noise is still there and giving me nightmares etc, so I've implemented three different algorithms in Max to try to address this issue; 1. a simple gate for discrete touches; 2. a lowpass onepole filter + zl stream/zl median; 3. downsampling.

I hope to be able to access both discrete and continuous touch data accurately, and, having pounded this forum and others mercilessly, still no success........please have a glance at the commented patch below and suggest anything (except [lbyl], it does lowfreq noise very well but not applicable in this instance): capacitors, welding rods, a hammer whatever!

That's two queries then i suppose; how to deal with ramping to, and vacillation around the 'real' touch value; and, how to access both discrete and continuous touch data.

Brendan (the 'touchpanel-noise guy', that's me)

Hallo
I'm afraid i'm still losing sleep over this one:

Brendan (the 'touchpanel-noise guy', that's me)


digital-filter-to-exclude-noisy-touch-data

Maybe you should look at the slide/slide~ objects. I believe that does what you are looking for.

Hmm, with IR sensors a capacitor near the sensor will smooth that junk. I can't recall the exact circuit off hand, but easy to find.

@k9 thanks for the suggestion, but as I understand it, [slide] does logarithmic smoothing, and lowpass filtering, both of which perform a type of interpolation on the number stream; in effect, the noise is merely delayed or interpolated, not ignored. But I haven't applied [slide] yet so i'll get back to you.

@Simon thanks also, but i'm using a resistive touch panel; I have various capacitor values and most texts I've referred to mention capacitors in the context of 50/60Hz mains interference and electronic interference from other devices, but again, I'll try the capacitor trick too.

sorry probably wont be able to help out much. Just interested in what your doing. What is it that you're actually making? A DIY touchpad or something? Like what you'll get in an iphone? Plus can you detect multitouch?

Have you looked at the smoothing numbers thread to see if there might be some ideas you could use?

https://cycling74.com/forums/smoothing-out-numbers

Have you looked at the smoothing numbers thread to see if there might be some ideas you could use?
https://cycling74.com/forums/smoothing-out-numbers


this is one of the core elements of my current PhD in accessible interaction design - I'm designing and prototyping a digital musical instrument interface for musician-performers with cerebral palsy; the touchscreen will control a variety of synthesis engines in MaxMSP, hopefully resulting in an interface/instrument similar to Roger Linn's Linnstrument, but, due to the limited capabilities of my participants, not availing of any multitouch functionality.

was hoping you'd drop by; of course, the solutions in your link form the core of my 'max utilities' folder - signal processing is where my project often gets stuck. I have resolved to 'ameliorate' rather than solve this issue as it is a perennial and fundamental issue with resistive touchpanels. Sometimes you just gotta put your hands up and say "Ok, I give up, you win".

The solution? Bigger pulldown resistors on all the inputs, a large for-loop 'averaging array' in Arduino, and finally [zl stream 3] ->[zl median]. Seems to be a good trade-off between noisy responsiveness and latent accuracy.

@Anneke
this is one of the core elements of my current PhD in accessible interaction design - I'm designing and prototyping a digital musical instrument interface for musician-performers with cerebral palsy; the touchscreen will control a variety of synthesis engines in MaxMSP, hopefully resulting in an interface/instrument similar to Roger Linn's Linnstrument, but, due to the limited capabilities of my participants, not availing of any multitouch functionality.

@Chris
was hoping you'd drop by; of course, the solutions in your link form the core of my 'max utilities' folder - signal processing is where my project often gets stuck. I have resolved to 'ameliorate' rather than solve this issue as it is a perennial and fundamental issue with resistive touchpanels. Sometimes you just gotta put your hands up and say "Ok, I give up, you win".
The solution? Bigger pulldown resistors on all the inputs, a large for-loop 'averaging array' in Arduino, and finally [zl stream 3] ->[zl median]. Seems to be a good trade-off between noisy responsiveness and latent accuracy.
Watch this space......

FWIW, I've put a milder version of my [Flatline] solution into the firmware of some 

 that I sell, with pretty good results when used for knob smoothing.

In the case of the touch screen, perhaps a simple passive lowpass filter before it hits the A/D of the Arduino would be good. Also, have you grounded any unused A/D inputs of the Arduino?

FWIW, I've put a milder version of my [Flatline] solution into the firmware of some hardware products that I sell, with pretty good results when used for knob smoothing.

In the case of the touch screen, perhaps a simple passive lowpass filter before it hits the A/D of the Arduino would be good. Also, have you grounded any unused A/D inputs of the Arduino?


if you are suggesting capacitors on the inputs, which values would you recommend? The touchpanel is rated at around 300-900 Ohms resistance I believe. In the past I've never had to force unused inputs to ground, but then I've never encountered such jitter before - but when the panel is dormant i.e. untouched, there is no noise or jitter whatsoever; the jitter stems purely from the minute fluctuations in fingertip contact location due to finger pressure and movement. While I'm here.....how should I connect the caps to the inputs; they are currently all pulled to ground via 10k.

It's sort of hard to guess at a filter without knowing what the rest circuit looks like.

It may be to "steppy" for your liking, but [flatline] comes close to meeting your requirements, otherwise.

Thanks; you're quite right - for discrete triggers [flatline] is ok, but less so for continuous data. Hmmm. I have a variety of caps here, from .01uF to .47uF, which I could try - despite much googling I can't find an example circuit. My circuit looks like this; do you know if the caps should be placed before or after the pulldown resistor on each read line?

Chris
Thanks; you're quite right - for discrete triggers [flatline] is ok, but less so for continuous data. Hmmm. I have a variety of caps here, from .01uF to .47uF, which I could try - despite much googling I can't find an example circuit. My circuit looks like this; do you know if the caps should be placed before or after the pulldown resistor on each read line?

A wild guess here but have you tried hooking up a coil/inductor. Definitely no expert but i believe this is the electronical equivalent of [rampsmooth]

digital filter, to exclude noisy touch data?