Touch screen interface

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    Learning and working on learning more!


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    This aliexpress listing sells not touch screens, but only touch panels. Like a transparent piece of glass that you strap to your screen. Also, according to the description there is no controller for it, and since this is basically a replacement part for some Chinese tablet with a weird brand name, there will be some problems with obtaining a controller.

  • Hey, I dont know if would work, but I have more of those 7" LCD linux PC that i donated to that space. AND I have the glass and USB adapter. If you want one you can have it the next time I ship something to Kamloops.

  • @hdsheena I am not sure if you are aiming for something ultra portable or just a good drawing and note taking medium. If you goal is the second, I would suggest investing in a laptop with a good built-in wacom tablet. I got an older fujitsu laptop for this exact reason. In the past I have had several lenovo and IBM laptops with wacom pen. All of them have served me good under Linux.

    My two favorite programs for using the pen under linux are MyPaint (infinite canvas with very good selection of pressure sensitive brushes) and Xournal (for taking notes and annotations on top of pdf files).

    However, I have learnt that just having the wacom pen does not automatically make me good at drawing :smile:


    Can you explain more what your use case is?

  • I am interested in playing with such things! :) To be able to pick something up, and learn how to use it. The best part for me is not just to use it in a project but to also share the knowledge or to help others that might want to use one.

  • I have a bit of experience with the resistive 4-wire interface… You can get a usb driver for them, but if you have 2 gpio pins, you don’t really need it. Each axis is a pair of wires. If nothing is touching the screen, the pairs show up as an open connection. If you touch at each corner of the screen, you get resistance on one pair… High resistance at one end, lower at the other. Anywhere in the middle of the screen, you will see an X resistance, and a Y resistance that is roughly linearly proportional between the high and low for that axis.

    So you set up a simple voltage divider for each axis, and use one analog pin per axis. Calibrate the readings one time and you have a touch screen. Arduino can read it easily. Raspi should have no issue. Last time I was messing with it, we were replacing “A bunch of buttons and a scanning matrix driver circuit” using a bunch of digital inputs with this… Printed a nice “Button template” on the laser printer, put the touch glass over it, and called it a user interface.

    In @hdsheena 's particular use, I think that possibly a protective shield goes over the glass, then a sheet of paper. Rely on the pressure of the pen/pencil on the paper to read through to the touch interface.

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    Basically, I want to be able to write on paper as ‘normally’ as possible, but have my writing fully digitized. Less than a couple pounds for portability for sure…

    Learning and working on learning more!


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    Just picked these up from the post office!

    Learning and working on learning more!


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    @trunner do you still have 7" LCD linux PC screens and are you selling them? (how much)?

    I have been looking at setting up a car computer for my VW but have not found a screen yet.

  • @Chris they’re a whole computer… I think we have two of them at the space if you want a project to figure out how the hell they work.

  • That sounds like fun! :)

  • @Chris Sorry, been way too busy at work. Yes I have a bunch kicking around. You can have one if you promise to teach a class at the space on whatever topic you feel most comfortable in.


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    @pierre this sounds interesting and worth taking a look at. Are these units in an obvious place at the space?

    @trunner sounds like a great offer. Next time I am in the space I will take a look at the existing units and see what is what.

    @Ron_Ron I recently spent the day traveling in someone else’s vehicle all day for work and it had all the latest technology in it so it got me thinking …

    When I originally converted the van to waste vegetable oil I built a crude arduino board to monitor the system and do the switchovers. It worked (kind-of) but was a bit clunky so I tore it out. I’d like to put something together now, commonly available features appear to be:

    • OBD 2
    • WVO switch over
    • sound system to android phone
    • GPS
    • backup and dash cameras

    For now I could really use ODB 2 and GPS so that would be my focus.

    Something like this running XBian? (there are a lot of projects on the internet now).

  • I’ve got similar ideas about an awesome car-puter setup… I really want wifi-enabled linux box onboard. Initially wired to the stereo system, and cameras.

    For adding GPS, I’m very tempted to acquire a spare ebook-reader to mod:

    The Kobo ones that I’ve taken apart have a TTL-voltage serial port inside, clearly marked that just needs wires soldered to it. They run an ARM with linux, and the recent ones have touch-screens with really nice e-paper displays. They’re popular in the glider community because they are full-sun readable and use little power (they run them from batteries)… All of my Kobo readers are hacked enough to run ssh so I can scp books back and forth over wifi. Picking up a mini online to use as a 5" map that tracks where I am seems really cool. Failing that, I’d be tempted to get an e-ink display with an SPI interface and wire it directly to the gpio pins. E-Ink is interesting partially because it is tolerant of extremely slow refresh rates, it would work with very minimal microcontrollers to drive it, or on an idle interrupt in an otherwise heavily loaded system.

    I don’t need fast refresh on the map, since I picked up a very inexpensive rearview mirror with a composite-fed LCD in it for the cameras. I could get away with wiring a single camera directly into the rearview, but I’d like to be able to select from several cameras, and I’d like to be able to read from a sonar rangefinder and overlay data onto the video. So I plan to use USB to composite devices to read the video stream, then do a bit of light processing on the PI and punch it out the composite port. My 20 year old next cube could do this, I suspect that the PI should have no difficulty with it. If it does, designing a tiny hardware video mixer that jacks into a GPIO pin would not be hard at all. Composite is easy to handle in analog circuits.

    I want a couple of beefy solid-state relays to run onboard battery-charging, block heaters, and the 300W 120VAC ceramic heater in my cab. This thing is the single greatest vehicle upgrade I’ve ever done. I have it on a block-heater timer now, half an hour before I leave for work, it comes on and warms up the cab. Snow falls off the vehicle, windows defrost and defog. I get to sleep 20 extra minutes every morning and go outside to a warm vehicle, no matter how cold and shitty the weather is. A thermostat-controlled heater that will warm hundreds of cubic feet of home is worth about 30 bucks. It will not have to work hard to warm a vehicle. And being ceramic-element driven, it has a negative thermal coefficient, so it is not prone to thermal runaway like a nichrome heater… Much less risk of fire.

    The other thing that I’d love to add is a GSM modem, so I can put a $15/month pay-as-you-go koodo SIM in the truck and have unlimited SMS messages from the vehicle.

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    Awesome! Your plans far outstrip mine … I am thinking of starting with the new RPI 3 (or something similar) because it has wifi and bluetooth (I think).

    Where did you get the rearview mirror?

  • Yep, Pi-3 is a solid option. Do you have a decent source of them?

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    RPi 3 best source I’ve seen so far …

    I figure after exchange it will not be much better buying outside of Canada.

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