Using Cheap Displays With The Raspberry Pi

The Raspberry Pi B+ has a native VGA connection. Sure, it’s hidden away in binary blobs and device trees, and you need to wire up the GPIO pins just right, but it’s possible to connect a VGA monitor to a Raspi B+ natively. For the brave, smart, or foolish, this means you can also drive raw DPI displays. [Robert] had a few of these dirt cheap displays sitting around and decided to give the entire thing a go. It worked, and he’s written down how to do it.

One of the chip architects for the Raspberry Pi, [Gert van Loo], was exceedingly clever when designing the Pi. There’s a parallel interface in the chip that, when combined with a few dozen resistors, can drive a VGA display in addition to the HDMI display. Screens with a Display Parallel Interface are actually pretty similar to what the VGA spec calls for. The problem is, hardly any of this is documented for the Raspberry Pi, and finding it means trawling through forums.

[Robert]’s example circuit uses a 5″ display from Adafruit, a 40-pin breakout, and a bunch of prototyping wires. Setup requires grabbing a cut down version of the device tree used for the Raspi VGA breakout board, setting the output format, rgb order, and aspect ratio of the display, and wiring everything up.

What’s interesting here is that [Robert] reproduced this project from scratch, and found that any display with a 40-pin DPI connector will work with the Raspi, provided you have a datasheet. That’s pretty cool; these displays can be cheap, and since we don’t yet have a proper DSI display for the Pi, this will have to do for now.

Video below of [Robert]’s inspiration for this build, [Ladyada].

63 thoughts on “Using Cheap Displays With The Raspberry Pi

  1. Someone needs to build a pi plate for these. I’d gladly pay $25 for one so I dont have to deal with the evil that is those flexible ribbons and the microscopic pitch of the socket pins.

  2. Given the fact, that the breakout board alone costs $10, but you can buy 7″ TFTs with HDMI converter board for $21 from Aliexpress, this isn’t really a bargain.
    The same display with USB touch will cost you $40.

    So unless you already have a nice TFT with parallel RGB input, or can get them for free, you better go the HDMI way.

    1. Agreed. I love how most of these hacks claim to save money but in reality generally cost the same or more and require a TON more work than just buying a solution off the shelf. I’m all about diy when it saves me money or results in a better end product… but when it doesn’t…..

      1. Hackaday should start posting articles about how to buy a USB touch screen and plug it in to a PI then.

        That’ll go over well with the whiners.

        “I’m all about diy when it saves me money or results in a better end product… but when it doesn’t…..”

        What about when it results in an absolute metric shitload of LEARNING?
        Is it OK with you then?

        1. Of course it’s absolutely okay to do such a thing just for fun, for learning, for teaching, etc. But when a solution claims to be cheap, it must accept to be compared to cheaper existing ones.

        2. It’s not self-edification if it’s stored somewhere in the HaD hive-mind, apparently.

          Seriously, everyone should have the experience of setting up an SoC raster blaster to work with an off-the-shelf LCD at least once. Also at most once.

      1. Here you are:
        Version without touch:

        Version with (USB) touch:

        The USB touch controllers are normally supported by actual Linux kernels.
        Some vendors even put a preconfigured SD card image on the CD.

        If 3.2″ is enough for you:

        These also come with a preconfigured image and run out of the box.

        1. Have you bought from that particular seller before, or just similar products? I have never used aliexpress and would hate for my first experience to go poorly, so I would appreciate feedback on the seller if you have any. Thanks.

    2. I, for one, find this INCREDIBLY useful both in that it doesn’t occupy the HDMI / composite output, but also it really DOES in fact save money, at least in my case.

      From the standpoint of saving money, my local thrift stores (Goodwill, etc.) pretty much 100% of the time have at least a few 7″ digital picture frames laying around which, 90% of the time, contain a 6-bit or 8-bit parallel RGB LCD.. and almost every time are priced well below the $10 mark (frequently, below $5!). This is a great source of these both at a cost savings even if you take into account the ADA Fruit TFT Friend ($10 + $5). And faster than waiting for something to arrive from china, with potential quality concerns and limited ability to return, etc. If I need touchscreen, sometimes those can be found at thrift stores as well… but if not, ebay or alibaba can just as easily source only the Touchscreen overlay for <$10, bringing total cost still well under $30 still less than the complete product and in a much smaller space (most of those cheap Chinese controllers are huge!)… and going this route, I have a physical chassis that I can choose to reuse if desired, or scrap out if I want to customize. And that is without getting into the aspect of recycling / re-purposing something vs buying something "new".

      So I personally think this is definitely both very useful and a potential bargain.

  3. Instead of saying that the Pi has a native VGA output that can be used as DPI interface, wouldn’t be more correct to say it has a native DPI interface that can be hacked into a VGA using some resistors ?

    1. Depends on the laptop LCD… Many laptops these days use other methods which reduces wire count between the controller and the LCD, due to space limitations through the hinge.

      1. You’d think so, but I would put the diacritics in naive.

        Human editors miss stuff too. There are processes you can use to make sure there are no errors, at all, in anything. Those processes take time.

        These processes are not limited to publishing it on the internet.

        Also, I have an edit button for my comments.

        1. Continue missing stuff Brian, else the comments section will be a no mans wasteland, with nothing for anyone to bitch about. Damn grammar and spelling Nazis. How about worrying about the articles content, rather than the small mistakes.

  4. What a shame. Another raspberry pi.

    The only thing I ever see them used for is emulators and Internet radios. But now someone did something clever, which I will give them kudos. But it’s a hack that really isn’t necessary. So im left unimpressed yet again. I want a reason to buy one; they can be used like an overpowered microcontroller, and operate like an underpowered computer. Such and identity crisis.

    1. I’m looking into using a Pi to control a robot if I ever get around to building the robot :P
      I honestly thing a micro controller wouldn’t quite be able to handle what I plan on having it doing and a laptop would probably be a bit bulky. Course it is in theory large enough that the extra bulk probably wouldn’t slow it down any. I’m also looking into using a C1 in an ROV, originally I had planned to use the Pi but there were some design limitations* that even the Pi2 didn’t seem to resolve that left me looking elsewhere and the Beaglebone was a bit pricey.

      *Like the Ethernet being affixed to the usb bus and being 10/100 instead of gigabit. Being faster and not having to fight for resources to send video on the same bus as the USB cameras trying to capture said video. Sidestepping two potential bottlenecks right out of the gate is a definite plus, not to mention it is a bit faster and boots like greased lightning with the eMMC (went with the smallest they had just to hold the OS). The boot time being a pleasant surprise I wasn’t planning on taking advantage of until someone pointed out you could use the eMMC and the at the same time. Which gave me the really fast boot and lets face it if you have a robot under water and you want/need to reboot it… you probably want/need to do it as fast as possible. Plus it freed up the MicroSD slot for cheaper bulk storage, neither of which ends up competing with resources on the USB bus.

    2. Not sure why you consider that an identity crisis. They are a link between overpowered microcontrollers and underpowered computers. My Makerspace is using one as the brains of a pinball machine. I’m using one for a “webcam” that needs dialup (uploads a few images per hour). And I plan on using a Pi2 for my kids to use Scratch on (currently using a Pi, but it’s slightly too slow). They’re much cheaper and smaller than an underpowered computer (plus, no moving parts), but perfect for applications where you would otherwise use an underpowered computer.

    3. “The only thing I ever see them used for is emulators and Internet radios. ”

      yeah whatever, infoworld has a whole list of useful applications for putting raspberry pi in the server room. wow, just google “raspberry pi applications” but then you wouldn’t be able to howl like that

      “I want a reason to buy one”

      Hey if you have money burning a hole in your pocket, feel free to paypal it to me. Most of us do it the other way around, we have a problem that needs solving and then we find a solution to it.

      “Such and identity crisis.”

      Such a language crisis!

        1. Gert Van Loo holds a title of Broadcom Senior Principal IC Designer, I think he even said in one of the interviews he is responsible for BCM2835 technical support internally at the company. He also designed first Pee prototypes (pcbs).

  5. I am looking for a solution like this to build a portable Pi in a laptop like form factor. Does anyone know if you can drive the display with power coming only from the Pi? (which is actually powered by a usb powerbank)

  6. Another option for cheap screens, old digital picture frames.
    These typically break because some stupid phool connected them to the wrong power supply.
    Or the backlight controller/tube goes bad, have seen this a few times too.
    A good protip, rip open a Philips “40W” 4 strip type LED bulb or simply buy the emitter strips on greedbay.
    its possible to actually make a replacement strip tube which fits where the old one used to go and emits enough light @ 10mA 28V or less to make driving it with a single MC34063 chip feasible.
    The added advantage is that broken LED bulbs can thus be recycled and avoid wasting the $$$ emitters.

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