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Sainsmart 3.2 TFT + PI = Frustration

e14 Contributor

I an a NOOB. No two ways about it. But I do know that I dont want to depend on shields to get things added. That being said:
I have a 3.2" Sainsmart touch sensitive TFT display and I want to use it with my PI. this is proving to be next to impossible as all the guides out there dont do a very good job for someone at my skill level.
I am hoping to lean on this amazing community to help me with some answers. I need to know how to pin the display to my PI and what drivers I will need to push it. I am asking this as we are mentoring some kids this summer in all things STEM and I thought it would be a cool takeaway for all of them to build a miniature MAME (roms) gaming box. Just a little something to bridge the gap! IF ANYONE could help I and the kids would be greatly appreciative. Just keep in mind any response will have to be VERBOSE as I am a noob image. I have attached all the files i have on the display.

Thanks in advance!    

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  • in reply to e14 Contributor

    Thanks for that contribution Jim,

     

    That adapter might indeed do the job, but there are a couple of things there that give me second thoughts.

     

    1) There are no connections for the SD Card slot. That may not matter at all, there is already plenty of storage on the Pi.

    2) The documentation for the adapter specifically states that it is not compatible with their ITDB02-3.2S LCD screen, which according to my reading is the closest in spec to the one Todd has.

    3) The cable solution is going to be rather bulky if we're trying to create a hand held MAME box.

    4) The pinouts for the LCD end make sense, but the Pi end specification is off in the weeds. I'm sure its good, but I can't interpret it from the info on the site. I'll need to root about in the documentation to understand how they've hooked it up.

     

    Observation 2) is odd. The same documentation specifies that their ITDB02-2.4E LCD *is* compatible and as far as I can see the pinouts are the same between the two boards on the site (and the one Todd has for that matter). OTOH, the demo shown in a linked video is showing exactly the same output as one of the example images on the LCD which (we think) Todd actually has. This suggests there is a good chance it would work despite the statement on the itead web page.

     

    One very useful resource on your link Jim, is the example source code which will enable us to get up and running much more quickly.

     

    So, over to you Todd. Will this cable adapter work for you, or are you looking for something neater? If the latter, my idea was to make a custom adapter board that would allow the display to fit neatly over the Pi. That will mean firing up KiCAD (a free circuit design tool), designing it and getting some PCB's made (surprisingly cheaply too). The kids might enjoy that as well, but it will inevitably take more time (PCB turnaround time is about 3 weeks). Let us know which way you want to go.

     

    BTW, don't be put off by the KiCAD route. I have quite a lot of experience with it and with getting PCBs made. It's a real option so long as the extra wait for the boards to arrive is acceptable.

  • in reply to guzunty

    Derek,
    we are all in for the kiCAD route image I am not scared whatsoever, in particular with such helpful folks! By shield I meant snap in board to avoid having to solder, et. al... I want this to be made, not snapped in!

    Please let me know how we are to proceed... Ii havent put anything out to the kids yet and they are literally about to burst. I think ill give them a hint today image I have some blank PCBS and dont mind using them for a prototype... but I LOVE your idea of sending this out to get printed. Granted I will still require the kids to understand the logic. We would love to have the touch screen available and the SD card, however I cant really see a good use for the SD card, but if you can let me know....It starting to smell like pine trees, must be that christmas feeling image THANKS IN ADVANCE!!!\\\\\\\\

    +todd

  • in reply to e14 Contributor

    Hey Jim!

    Thanks for stepping up. Between you and Derek I am positive we are going to get this done. I want the kids (and me!!!) to get as much from this as possible. Most importantly we arent scared to break some stuff / fix some stuff.
    TODD

  • in reply to e14 Contributor

    Alright! Let's get this party started.:-)

     

    I assume you can split the LCD board from the Arduino shield at the 40 pin connector. For compactness, we'll want to discard the shield if we can, so please confirm that you can split the display off the shield.

     

    Now for some thoughts on the board design. Where are you from, Todd? I'm European, so I like to work in metric units. Let me know if you would prefer to switch to imperial.

     

    1) The place where I have my boards made has a range of size/price cutoffs. The smallest size board is 50mm square. Go 1mm over that and the price doubles. The minimum order is 10 boards, but we may acquire other interested parties as we progress so that we can share the cost. The cost is pleasantly surprising anyway.

     

    2) 50mm on a side is tight for a 40 pin connector, but I think we can pull it off. To fit both connectors in, we'll need to have the 40 pin connector overhang the Rasperry Pi SD card by about 7 or 8 mm. My thought is the display will sit directly above this, so that should provide a nice fit with the SD just protruding from a slot in a case (I assume you have your own ideas in the area of casing). This approach won't fit in a standard Pi case, but I'm struggling to imagine an of the shelf case that would accomodate the LCD anyway.

     

    3) To minimise thickness, I suggest we use what is called a bottom entry surface mount 40 pin connector. This will allow the LCD display to sit directly on top of the adapter board. The whole assembly will be no more than the height of the yellow audio connector on the Pi plus the thickness of the LCD display itself. In other words, the adapter we create will nestle down beside the audio connector and itself add no height to the assembly at all. Let me know if you have trouble visualising it and I'll send you a sketch.

     

    4) The Pi has limited IO. 17 GPIO's to be exact. To talk to the LCD display in 8 bit mode requires 12 signals, maybe 11 if we're lucky. To talk to the touch screen we need another 4. That's 15 or 16 GPIO's used up. This does not leave much room for other functions.

     

    5) Partly because of the above, I recommend that we do not implement the touch screen. I do have an open mind, I think the touch screen would be quite nice for scrolling through the games etc. However, my experience of actual game play with touch screens is that it is frequently less than satisfying. Old MAME games were designed to have buttons you physically pound, I have my doubts that we could make a great experience using only the touch screen. Also, If we forget about the touch screen, we free up the extra IO to sense some physical buttons.

     

    6) There may be room add some 'insurance' onto the PCB design in the form of a programmable logic chip like this: https://github.com/Guzunty/Pi/wiki (Disclosure: I curate the Guzunty GitHub site). The actual chip we would use would be physically much smaller than the one shown on the Guzunty web page, the one shown there is designed for easy home assembly. What I suggest is that we design the board so that we don't have to populate the place for the chip unless we find that video performance isn't good enough, or we are short of inputs etc. If necessary, the logic chip can then be soldered in later and programmed to accelerate the video display or provide some IO expansion or whatever. That is why I call it 'insurance'. If we find we never need it then great, it didn't cost us anything (unlike real world insurance :-) ). Just a set of pads on the PCB.

     

    7) You'll want to download a copy of KiCAD so that we can share designs. Element14 would rather we used Eagle I am sure, but I like KiCAD better because it is an open source tool.

     

    Thoughts on the software side.

     

    I am an experienced C, C++, Java developer. I've built MAME from source on the Pi but I have never dug in under the hood. We may have to get on some of the MAME forums to enlist some help in this area. There are three areas we need to address: input/output, video and sound. The first has been done, I just need to go find it again. I'm not aware of any work done to stream MAME video to alternate display devices, but it can be done, I'm sure.

     

    That leaves sound. What did you have in mind here? MAME without sound would be like apple pie without icecream. :-) Pi has the yellow headphone connector. I haven't listened to it, but I've heard its not great compared to the digital audio the Pi produces through the HDMI connector. Taking sound from the HDMI connector would (IMHO) be rather clumsy. One less obvious (and more ambitious) alternative is to add J5 onto our PCB and create traces for an audio codec and a small audio amplifier. Some of the pins on J5 can carry an I2S digital audio stream.

     

    One other area we need to think about is power. What type of battery will we use?

     

    Wow, a lot to cover. I suggest we design our plan so that we can get something working:

     

    - 8 bit video (i.e. accepting that it may be laggy)

    - PCM sound through the headphone socket, MAME era games were not that hi fi anyway.

    - Simple mechanical player button inputs which double for game selection. This means we don't need to develop any code for the touch screen initially.

    - Wall wart power only for now.

     

    Let me know what you think,

     

    Derek