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Interfacing with a 4-pin Touch Screen Interface — Parallax Forums

Interfacing with a 4-pin Touch Screen Interface

Jim FouchJim Fouch Posts: 395
edited 2008-06-01 07:47 in Propeller 1
I'm working on interfacing with an Pioneer DVD Navigation system (AVIC_D3)·I'm installing in my truck.

This system allows the display of a video input. I'm going to use a Prop to generate· TV display and feed that into the DVD system.

The System has a 4-pin Touch Screen. When a video signal is being displayed I don't think the system does anything with the touch screen. I'm just wondering how hard it would be to read the position of the touches. I want to do this w/o interfering with the system. I'm only going to use the touch data when MY screens or being displayed.

I have attached a picture of the 4-pin connector.

My plan first is to probe the 4 pins with a scope while running the system. Then, if I can make sense of the signals, would be to read them into the prop with an ADC.

Does this seem doable? Or am I just crazy???



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Jim Fouch

FOUCH SOFTWARE
Touch Screen Connector.jpg
939 x 897 - 219K

Comments

  • Paul BakerPaul Baker Posts: 6,351
    edited 2008-03-07 21:39
    It's certainly possible, someone just interfaced with a 5 wire touch screen, how easy it would be I cannot answer.

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    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • Bob Lawrence (VE1RLL)Bob Lawrence (VE1RLL) Posts: 1,720
    edited 2008-03-07 22:30
    The URL below should lead you to what Paul is referring to:

    http://forums.parallax.com/showthread.php?p=713258

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    Aka: CosmicBob
  • RinksCustomsRinksCustoms Posts: 531
    edited 2008-03-07 23:01
    you may also want to look at Fujitsu p/n# N16B-0558-B270 (4 wire RS-232 data), Mouser.com carries them. You can also link to the PDF datasheets. If you can follow the traces to the controller chip then try googling the P/N# of the chip (this may take a few atempts, but it may link you directly to a PDF datasheet of that chip where you may discover you may be able to "listen" to the output of the chip to get your screen pos that way. The better way, if the stereo turns off the touchscreen durring video in, would be to read the resistance of the screen resistors (RX & RY) with the prop in an RCTIME sorta way to determine your fingers location. a dirty/crude technique, but should work.

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    E3 = Thought

    http://folding.stanford.edu/·- Donating some CPU/GPU downtime just might lead to a cure for cancer! My team stats.
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2008-03-08 00:42
    Go for it. Try it out. Near the bottom of my "Would like to do list" includes a four or five wire touch screen object. It is really at the bottom of my list, so I am interested to hear how your success is.

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    Timothy D. Swieter

    www.brilldea.com·- check out the uOLED-IOC, an I/O expansion for the uOLED-96-PROP
    www.tdswieter.com
    One little spark of imagination is all it takes for an idea to explode
  • RaymanRayman Posts: 14,130
    edited 2008-03-08 20:15
    I think the 5-wire may be superior to 4-wire touchscreens... In any case, I think it would be much easier to connect directly to the Prop (without using any controller boards). With 5-wire screens, there is just 1 analog and 4 tri-stated digital signal to control. So, you can do it with just 6 Prop pins.
  • RinksCustomsRinksCustoms Posts: 531
    edited 2008-03-09 19:11
    Rayman said...
    I think the 5-wire may be superior to 4-wire touchscreens... In any case, I think it would be much easier to connect directly to the Prop (without using any controller boards). With 5-wire screens, there is just 1 analog and 4 tri-stated digital signal to control. So, you can do it with just 6 Prop pins.
    I agree, you could even keep the AVIC's functionality by using a multiplexer on the touchscreens 4 lines to switch between the AVIC's touch reader and the prop. I must say, you got some big ones opening up a $1000+ A/V stereo!shocked.gif

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    E3 = Thought

    http://folding.stanford.edu/·- Donating some CPU/GPU downtime just might lead to a cure for cancer! My team stats.
  • Jim FouchJim Fouch Posts: 395
    edited 2008-03-09 21:24
    Yeah, it's a bit scary, but the rewards if I pull it off are going to be awesome. I'm looking at interfacing with an ELM327 chip to pull all the OBDII data off and display it on the AVIC. I'm already reading the FI and speed pulses to tell what the fuel consumption is. It's going in a 2008 Trailblazer SS.

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    Jim Fouch

    FOUCH SOFTWARE
  • Jim FouchJim Fouch Posts: 395
    edited 2008-03-10 12:27
    Well, I was able to make my connections to the stereo over the weekend and think I can pull this off. The unit only puts up a single button in the lower right when you touch the screen when in Video mode. This will allow my screens to run pretty much the entire screen w/o interfering with the main unit.

    This signals I’m getting are going to be a bit tricky to read. They are a 5 pulse burst that the amplitude changes with touch position. These pulses run 2ms in width and if the finger is held it will repeat with a 15-20ms pause between bursts.

    I'm thinking of having one cog run a MCP3304 to always capture analog from these two inputs. Another cog would use a comparator to trigger a 1ms delayed reading of the Analog values from both X & Y.

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    Jim Fouch

    FOUCH SOFTWARE
  • CassLanCassLan Posts: 586
    edited 2008-05-30 21:18
    Jim,

    How did you make out with this project? I'm thinking of doing something similar.

    Rick
  • Jim FouchJim Fouch Posts: 395
    edited 2008-05-30 23:39
    I've had the AVIC installed for about 1-1/2 months now. I have not yet interfaced into the touch screen. I'm going to be doing that this weekend. Keep your fingers crossed..... lol

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    Jim Fouch

    FOUCH SOFTWARE
  • jazzedjazzed Posts: 11,803
    edited 2008-05-31 02:29
    Hi, I bought a monitor with 4 wire touch screen hoping to get something working in the near future.
    Looking around for some theory I found the AD note below which describes a 4 wire touch screen.
    They are of course trying to sell their ADC. Would a pair of Propeller ADC circuits also work?

    http://www.analog.com/library/analogDialogue/archives/35-04/touchscreen/index.html

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  • Mike HuseltonMike Huselton Posts: 746
    edited 2008-06-01 07:47
    See this for an idea of rs232 add-on touch panel costs:
    http://store.earthlcd.com/LCD-Products/Add-On-Touch-Screen-Kits

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    JMH
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