Affordable capacitive touch screen that can be powered from USB

[Experimentalist]

Hi

Has anyone come across an affordable capacitive touch screen that can be powered from USB for use in Teensy projects?

I have a resistive touch screen and have seen reference to many more but I have seen no mention of capacitive touch screens in the forums.

My hunt has uncovered this:

http://www.newhavendisplay.com/nhd50800480tfatxictp-p-5018.html?zenid=n8pnopsvc5d4u6n7nm28a95op1

It looks great and I thought reasonably priced but was then sad to see that the LED backlight needs a 23.1 volt supply! Stopped reading the spec at that point as I am looking for something that can be powered from USB.

Any ideas?

 

[cartere]

uLCD-43-pct from 4dsystems about $185 has capacitive touch screen.

 

[Experimentalist]

uLCD-43-pct from 4dsystems about $185 has capacitive touch screen.

Good call but not really affordable for my project. This unit has many features over and above the screen. I am looking for a screen with the touch panel that can be supplied from USB power and the best price. Hoping to find something nearer half that price or less. Hoping may be all I ever do but I will keep looking

 

[nox771]

the LED backlight needs a 23.1 volt supply! Stopped reading the spec at that point as I am looking for something that can be powered from USB.

23V doesn't preclude it from being run from USB. It just means you need a boost converter to get from 5V to 24V. Current draw on the LED looks like 20mA, so it is not an unrealistic current draw for a boost circuit. I think the bigger concern with that display would be hooking into whatever that flex connector is.

edit - I should mention the last time I ran a boost circuit off USB the crosstalk killed the data lines - so it might take a couple USB cables to do the job (one for backlight power, another for data). YMMV.

 

[Experimentalist]

23V doesn't preclude it from being run from USB. It just means you need a boost converter to get from 5V to 24V

Do you have any recommendations regarding the boost converter? Any ideas on the calculation for the resulting current draw on the USB 5V rail? Is it just:

(24 / 5) x 0.020) = 0.096 = 96 mA ???

I think the bigger concern with that display would be hooking into whatever that flex connector is

The connector for this is freely available and cost around 25 British pence which is somewhere around 40 cents I think, just search for "40pin 0.5mm pitch FFC Connector". The manufacturer also makes a breakout board which you can see at the bottom of the page I originally posted but here is a direct link:

40pin 0.5mm pitch FFC Connector breakout board

So that should not be an issue. I will be looking to combine it all onto a custom PCB in the long run, if I ever get that far . . .

 

[MuShoo]

Well, here's the thing - I highly doubt that screen you linked will work 'out of the box.' You're going to need 33 pins on your controller chip (the Teensy) to drive the thing - 24bit RGB values, and then various control signal pins. You'll also most likely have to write your own driver to actually deal with screen communication. And touch communication. The datasheet seems somewhat detailed, but assumes a lot of knowledge about interacting with screens on that level already.

The connector may be easy to get, actually making it work is probably going to take a lot of time.

 

[nox771]

Do you have any recommendations regarding the boost converter? Any ideas on the calculation for the resulting current draw on the USB 5V rail? Is it just:

(24 / 5) x 0.020) = 0.096 = 96 mA ???

It would be something along those lines, but you would have to search datasheets for boost converter ICs to know (obviously boost efficiency is not going to be 100%). ~100mA is also quite a pull on a USB cable with 24ga wires, it might take some sizable input cap also. Again the datasheets and some experimentation req'd.

Instead of scratch building though, perhaps search first for some kind of off-the-shelf boost LED driver, something that could take 3-5V input, and output maybe 24V at greater than 20mA.

Maybe search here first: http://www.ebay.com/bhp/boost-converter

 

[Experimentalist]

Well, here's the thing - I highly doubt that screen you linked will work 'out of the box.'

I realise that it would not be plain sailing, but I am just trying to find something reasonably priced in the first instance and feasible to power from USB in the second. Since it is just a TFT display I had been hoping I may be able to use Henning Karlsens' UTFT library, now packaged with Teensyduino by Paul:

http://www.henningkarlsen.com/electronics/

However, I wanted to understand if it is even feasible to power that display from USB before buying one and spending any effort on getting it to work. I have not spent any time on that as yet but now you point it out it does not look to be compatible with the UTFT library mentioned.

Maybe search here first: http://www.ebay.com/bhp/boost-converter

Thanks for the advice, got this on order just to have a look at, run some tests, and throw in the project box.

http://www.ebay.co.uk/itm/LM2577-DC-DC-Step-up-boost-converter-4-35V-/130926346159?ssPageName=ADME:L:OC:GB:3160