silent button with distinct signal?

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phartmann
 
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silent button with distinct signal?

Post by phartmann »

Hi,
I'm working on a wearable project that has a number of switches in a button ladder circuit. The project requires switches that aren't clicky. I've tried 2 different kinds of silent buttons and the all seem to be sort of resistive, giving different analog values depending on how hard you press. If you're familiar with how the button ladder registers different buttons, you understand that this is not going to work. The switches need to have a distinctly connected or not connected state. Does such a thing exist that has this kind of action but is also silent?

Thanks much!

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adafruit_support_mike
 
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Re: silent button with distinct signal?

Post by adafruit_support_mike »

A common trick is to build an N-resistor voltage divider, then connect the switches between the ADC and different points on the divider.

If you have five switches, for instance, you can make a 5-resistor divider from, say, 10k resistors (total resistance 50k). Then connect your switches so each junction so the ADC will see 20%, 40%, 60%, 80%, and 100% of the voltage applied to it.

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phartmann
 
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Re: silent button with distinct signal?

Post by phartmann »

Thanks Mike. Yeah, I think you're describing is the same as what I've seen called an R2R resistor ladder circuit. But my question is about the compatibility of certain switches with this kind of circuit. See, when you even connect one of these https://www.adafruit.com/product/3101 to an analog pin and pullup, the values you see vary wildly depending on how hard you press it. It's not a definite on or off. The way these switches are put together there's kind of interlaced copper forks on a circuit board. The underside of the silicone has some conductive property. When the conductive part touches some or all of the interlaced forks, the conductive part helps make the circuit between the forks and switch is "on". You see this switch design in remote controls or keyfobs n stuff. I use quotes and bold "some or all" because when you're reading values from an analog pin, you see that the switch is almost like a pressure sensitive potentiometer.

I'm using the circuit from here: http://www.ignorantofthings.com/2018/07 ... istor.html Image

Maybe the R2R or N-resistor circuit is less susceptible to this effect? But what I'm seeing is that a soft press from one of the outer buttons might trigger one of the inner buttons in software. I think what I trying to ask was: are there silent switches that don't use the interlaced fork design? What are your thoughts? Thanks!


PS I'm considering using 6 ds2413 in series. But I think I'd be way out in the weeds. Not too many people doing this.

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adafruit_support_mike
 
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Re: silent button with distinct signal?

Post by adafruit_support_mike »

Try this instead:
switch-ladder.jpg
switch-ladder.jpg (47.68 KiB) Viewed 572 times
Assuming all resistors have the same value, you get a uniform, easily understandable distribution of voltages associated with each switch.

R-2R networks are useful, but are best suited to deciding what subset of switches are closed at the same time.

The resistor ladder you posted can work, but there's room to debate whether it's worth the additional complexity to save a single resistor.

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