Affordable touchscreens for AVR

Go To Last Post
15 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Freaks,

Does anyone know of affordable touchscreens to interface to AVR's? I am thinking of a project where I can use the touch screen to control a fan/motor. I would have "Start motor" and "Stop motor" buttons on a touch screen interfaced to an AVR. I can work with a small size screen (maybe half the size of an iPhone touch screen).

Thanks.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok I found one on Newhaven:

[url]
http://www.newhavendisplay.com/i...
[/url]

Has anybody used this with an M48?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I haven't, but it seems quite simple to me.

Basically you have to deal with two variable resistors. So you hook up the touchscreen as two voltage dividers and connect them to two ADC inputs. Simply continously do conversions and see if the voltages fall within a certain range for each displayed button. You probably want to include a function that converts it to x,y coordinates that are easy to check.

Don't forget to include an calibration routine ;)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

"there's an App[note] for that" ;)

http://www.atmel.com/dyn/resourc...

But if there's are fixed buttons, and you don't really need the screen. You can also make your own touch buttons. Look into the Q-touch studio [from Atmel] for a good starting point.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

npat_avr,

Did you not see the link I gave to ledsee.com in your other thread about GLCDs? Some of those have a touch overlay - also see Sparkfun.

Cliff

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for the info, guys.

@jayjay and glitch,
I will take a look at the app. note. (nice pun,glitch:)
Just thinking out loud here but I wonder if you could reduce the number of AVR inputs needed. Also maybe it is possible using input comparator and/or INT pins?

@cliff,
Thanks for pointing it out. I will look in ledsee as well.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You can reduce the requirement of pins from 4 down to 2 with an analog mux. You won't be able to use an INT, as the input is analog in nature. You could use the comparator to determine of the panel has been touched, but you will still need the ADC to determine where.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

glitch wrote:
You can reduce the requirement of pins from 4 down to 2 with an analog mux. You won't be able to use an INT, as the input is analog in nature. You could use the comparator to determine of the panel has been touched, but you will still need the ADC to determine where.

You can use INT to check when it is been touched and then read the position with the ADC. The AN explains the details...

Felipe Maimon

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Right, after thinking about it more, I realized that one could use the INT pin to detect a touch provided that the ratio of resistances of the screen and the internal pull-up work out.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Do we need some sort of conductive panel to use these atmel touch sensor chips? If so, is there such a thing as something conductive and see through, so I could make an auto gauge controllable by touching the screen?

Imagecraft compiler user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

It's called ITO (Indium Tin Oxide) used in both resistive, and capacitive touch sensors for display screens. [there may be other materials as well, but ITO is the most common]

And yes for the Atmel capacitive touch sensor, there is a conductive pattern that is required for the sensor to work. For a fixed button, this is often placed on a PCB that is mounted behind the "glass" Capacitive sensors will work through the front panel material, provided that the material itself is not conductive.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok I partially read the app. Bear with me but looks like what they explain is just the touch screen. Don't you still need an GLCD display below it to display your buttons?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not really, the display is only a guide for the operator :)

You could use just the screen as a touchpad as found on a laptop (though those work on a different principle).

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

npat_avr wrote:
Ok I partially read the app. Bear with me but looks like what they explain is just the touch screen. Don't you still need an GLCD display below it to display your buttons?

Well that's what I thought you were asking for, since you linked to a touchscreen for a display. If all you want is a fixed touch-button, look t the Qtouch library, and associated documentation. This will let you use capacitive touch switches, sliders, and wheels in your AVR apps. Basically it's a royalty free library that implements the code necessary to implement your own touch-sensor, without the need for an external IC.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok now I get it. Has anybody tried this new Qtouch library?