foot "mouse" / xy area..

[lokki]

hi,

i want to measure a given area on a floor on which i can move my foot around (x and y) axis and i get the distance from the lower left corner of this area.
in the end i want to control two synthesiser parameters with this. the area will be about 30 x 60 cm, though this is not final as of yet.

i considered different scenarios:

-build a wooden outer frame with a construction on it that can move horizontally and vertically and use encoders (connected to the construction with a string on each axis) to measure the distance each axis traveled from/to the 0,0 origin

-use two ultrasonic sensors and move around an object in a frame and measure both x and y distances to the frame.

-use a mouse that i repurpose for foot usage and get absolute position from the usb-mouse output.

since i would like to control synth parameters via midi, it should react with low latency.

i will aquire a teensy 4.1 board to have the usb-host available (for the mouse idea) and have plenty of teensy lcs around for one of the other ideas.


any ideas/inputs on what would work best?
i guess the encoder thing will be a bit fiddly, with the strings etc.
the idea with ultrasonic sensors will maybe not have a very smooth/low latency response? are there other distance sensors i could use?
i like the mouse idea the best, i have a logitech wireless mouse which is optical, but i am not sure that the teensy will recognize it and i don't know if it is easy to calculate an absolute value from the mouse output.

maybe i could also attach something like an optical mouse sensor directly to a teensy?

thanks

 

[Nominal Animal]

24" to 27" (diagonal) infrared touch frame with USB HID interface sounds suitable. A 24" 16:9 one is 531mm × 299mm or thereabouts, 27" 16:9 one is 598mm × 336mm. Many of these have multitouch, so you could use two or more "pucks" you can move on some hard surface, and the Teensy would track the relative movement of each (because it cannot differentiate between touch points), to control more than one pair of synth parameters. The downside is price.

I'm just a hobbyist myself and know nothing, though.

 

[lokki]

thanks for your input. as it turn out i found an old wacom drawing tablet which is quite large at a neighbours place. maybe i will try and use that. i will see if i can make the pen into some kind of puck as you describe it.

are there wacom intuos "drivers" for the teensy usb host?

 

[Nominal Animal]

As far as I know, these are pretty much standard USB HID devices. It would be informative/useful to see what kind of USB HID reports it actually produces, for example by running sudo evtest in Linux, selecting the correct device, and then looking at what it reports when you touch and press the buttons, because that might help if you do run into problems. But they really should provide rather standard USB HID packets. I do not know if anyone has a library for Wacom or touchpads in general, for Teensy USB host yet.

As to the puck, I'd suggest a literal puck made of plastic, with a conductive "nib" –– maybe a tiny ball bearing –– near the bottom. If you have access to a 3D printer, perfect.
These typically use capacitive sensing, so the idea is to have something conductive in the control puck. For best results, the cross section of the conductive thing should be relatively small, but extend away from the surface, so something like a 3D question mark, ?, shaped piece of thin copper wire, with the tip at the bottom center, then winding away from the contact surface in the puck, may work better than say a small ball bearing.

The puck shape should be almost flat at the bottom, of course, but on the top, it depends on whether you intend to have shoes on or not. For this, experimentation with a 3D printer would be useful. The puck does not need to be thick, but I'd definitely make it flexible in the thickness direction, so it (and not the tablet) absorbs any accidental stomps.

If the tablet supports multitouch, you can use multiple pucks, just remember that the tablet does not differentiate between the two; you need to do that logic yourself. (Essentially, whenever a new report comes in, you need to check which one was previously closer, since statistically that will be the one that moved.)

(In comparison, an infrared touch frame is just a frame, and it only detects "cylindrical" objects passing through the frame, so it would be more amenable to gig use, I think.)

 

[lokki]

thanks again. the wacom tablet has actually two device "endpoints" one being a mouse and the other a digitizer. you can use it with your hands and use some gestures, or with a pen. it is only absolute position with a pen, so i plan to use a modified pen as a puck. wacom uses a quite complicated active pen that gets its energy from the pad itself, so no battery inside. (some coils etc.) you get some buttons on the pen and pressure sensitivity (about 2048 steps i think on mine). so i don't think a simple conductive puck will work. but i have a 3d printer and i think i can modify (take apart) the pen and use its guts in the puck

great idea about the soft puck as well, i was thinking about something in that direction to absorb foot pressure and translate it to "hand" pressure levels.

the benefit of the tablet is that is is cheap (if i have to pay anything) and it is pressure sensitiv, so 3 parameters with one puck.

i don't want to give up on the infrared touch frame completely, do you have any source that has some available? here in switzerland i get almost no results, and the ones i get are from dubious websites with very bad reputation (fruugo.ch)

with the infrared touch frame i will loose pressure sensitivity, though i could build a pressure mat from velostat and copper, have done that before. i am not sure about the multiple puck idea, for live usage i imagine i will bump into other pucks pretty easily

also i am not 100% convinced those infrared touch frames will work that great with stagelight shining on them from different angles and fast light movements. they claim immunity to day/ambient light, but i can't imagine they tried it on a stage. but maybe the sensors are narrow enough in spectrum and do not pick up any other frequencies.