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I connected a 5V relay to an Arduino. It then opened and closed the relay, which had on a terminal (doesn't matter which one?) a wire that went to an iPhone' screen (with tin foil at the tip). On the other terminal I had nothing. The middle terminal had a wire that went to my hand.

The relay switched from floating to ground (from my hand), but the touch was sometimes not registered, sometimes it jumped around, and when it worked at best, the touch was registered, but the "touch end" didn't work even after the relay went to floating position.

Any ideas as for why this didn't work? I feel that either the relay is too big and disturbes the signal or the software behind the screen works in a way that doesn't allow this method to work.

Thanks!

Schematic: (70 ohms on the relay's coil)

Design

Circuit

Picture

W5VO
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OFRBG
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  • This sounds ... strange. You should post a photo, and a schematic - also, I'd like to know what the experiment is for. What parameters or functions are you gauging? –  May 05 '15 at 05:23
  • Have youu seen this other question about the same subject? http://electronics.stackexchange.com/questions/60385/how-to-use-a-capacitive-touch-screen-without-a-human-hand?rq=1 – JRE May 05 '15 at 12:14
  • @JRE Yep. I've made some research and found some attempts and one success. I tried to compare my attempt to the "best" one but it doesn't work as expected. Here's a video: https://vimeo.com/101571060 – OFRBG May 06 '15 at 02:31
  • I'm going to guess that the stray capacitance of the breadboard has done you in. The screen likely isn't registering enough of a change for it to consistently decide it is being touched. And I'm still not sure what this accomplishes. –  May 06 '15 at 03:06
  • @SeanBoddy the objective is to simulate a touch. – OFRBG May 06 '15 at 03:20
  • I can see that clearly. But you are standing right there. I don't mean to be snarky - I'm asking *why are you doing this thing*. –  May 06 '15 at 03:26
  • @SeanBoddy oh. I want to be able to send touches via Arduino to beat games like Flappy Bird via software. (The real end is DSP and software.) – OFRBG May 06 '15 at 03:33

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The problem here is likely down to poor coupling between the foil, the screen and the wire you are using. I would try again, replacing the foil with a piece of conductive foam, using adhesive copper tape to connect to the foam, and then soldering the other end of the tape to a piece of wire to connect to the relay.

I would also be sure to apply some downward force on the foam in order to deform it slightly, improving coupling with the phone screen.

stefandz
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