Position sensing button (spring loaded linear potentiometer?) - Page 1
Forum section: electronics / projects

author: mattybigback
author_rank: Contributor
timestamp: February 27, 2014, 12:36:49 am
content: Hi thereI'm trying (without much success) to find a part that is somewhere between a button and a potentiometer. The idea is that I can press down the button and the further down I press it the higher/lower the resistance. I want to connect it to the analogue pin of a microcontroller so I can read values from it and send it out as MIDI CC data.Does such a part exist, or am I going to have to build something? If it does exist can anyone recommend a particular part?Thanks

author: ajb
author_rank: Super Contributor
timestamp: February 27, 2014, 12:59:02 am
content: There are pressure-sensitive membrane resistors likethis, but they don't really offer any sort of tactile feedback since they have basically zero travel.Googeing "Analog pushbutton" brings up some interesting results--mainly for the industrial market, so probably spendy--like C&K'sHP series.I seem to recall seeing something like this done with fairly basic rubber dome switches, where the harder you pressed on the dome the more of the carbon pad on the inside of the rubber came into contact with the contact area on the PCB, thus decreasing resistance, but that would likely require a custom rubber mold.What quantity do you need?

author: mattybigback
author_rank: Contributor
timestamp: February 27, 2014, 01:18:06 am
content: Thanks for the replyI saw those membrane things and I thought about maybe using that as the basis of some sort of spring mechanism, but it's not really what I am looking for.I only really need one - it's for a personal project. Ideally I'd like about 5cm of travel so that it's big enough to be tactile, but small enough to fit under the hand. I'm trying to build a MIDI-capable Ondes Martenot, and I'd be using this sensor as the volume control. I've already figured out how to implement the slide ring (just a multiturn pot with a nice chunky wheel on it) so this is the missing piece.I might have to bite the bullet and build a mechanical solution.Thanks for your advice

author: Rerouter
author_rank: Super Contributor
timestamp: February 27, 2014, 01:31:56 am
content: What is stopping you from using a linear potentiometer? you screw a knob onto a rod, cut a slot in a close fitting tube for the rod, and glue the pot's arm to the rod, with a spring in the bottom of the tube, with the end glued up,an addition would be 2 pins in the rod to prevent it being twisted and limiting the range,

author: dannyf
author_rank: Super Contributor
timestamp: February 27, 2014, 01:36:35 am
content: There are plastic buttons that are touch / force sensitive.You may also look into those buttons used on cameras: they allow "half press" vs. "full press".Another idea would be to use inductance sensing: you push an iron rod into a coil and that changes its inductance. The output could be the frequency.

author: mattybigback
author_rank: Contributor
timestamp: February 27, 2014, 01:41:37 am
content: Yeah that sounds like a better idea actually - simpler than dealing with gears. I'm not so great with that kind of thing but I'll give it a go.Another solution I was considering was to use a rod on a pivot with a gear on the pivot, and use that to turn a standard potentiometer with some sort of spring to return the rod up. Sort of like an exaggerated morse key type thing.I've never used an inductive coil before, so I'd have to hit the books a bit, but it's an interesting idea.

author: ron
author_rank: Regular Contributor
timestamp: February 27, 2014, 01:51:46 am
content: You didn't state size or travel. How 'bout an old slot car controller?http://www.ebay.com/itm/LOT-OF-2-VINTAGE-BLACK-COX-SLOT-CAR-CONTROLLERS-1-24-SCALE-/310880992087?pt=Slot_Cars&hash=item4861f37b57

author: LukeW
author_rank: Frequent Contributor
timestamp: March 02, 2014, 04:00:02 pm
content: This is basically what you want. A bit pricey though.http://australia.rs-online.com/web/p/precision-position-switches/0317780/

author: Yago
author_rank: Frequent Contributor
timestamp: March 02, 2014, 05:30:50 pm
content: Have a look at Playstation/xbox controllers.They have a analogue push buttons.The ones I have seen are a button sliding on a rail, turning a cog to a pot, quite a compact thing.Might be a "bodge" but the controllers are dirt cheap, and broken ones free!