Large color LCD?

Discuss development of drivers for external hardware and components, such as LCD screens, sensors, motor drivers, etc.
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engineer
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Large color LCD?

Post by engineer » Tue Jan 14, 2020 4:32 pm

I am looking for a largish LCD that has an existing pyboard driver.

Something big enough to do text editing on -- typical laptop display or business monitor size would be fine, not looking for a giant screen.

I do need color, backlighting, and the ability to set the color on individual pixels. (Some sort of text mode would be nice but I can live without it.)

Somewhere in the range of 1024x768 to 1920x1080 pixels would be ideal, but I would be willing to go smaller or larger.

Don't care if it has a case, but having one would be a plus.

I was talking this over with a coworker and he suggested that if I couldn't find a suitable LCD I could try interfacing a Raspberry Pi Zero with a pyboard, hooking up a cheap HDMI display, and cobbling together some sort of software on the Pi that makes it look like an LCD display to the pyboard. Stupid idea?

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pythoncoder
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Re: Large color LCD?

Post by pythoncoder » Tue Jan 14, 2020 6:07 pm

This RA8875 driver supports colour displays upto 7 inches. I'm not aware of anything bigger. The issue tends to be frame buffering: displays with large numbers of pixels can require large buffers outside the capability of microcontrollers. Others perform the buffering on the display and provide local firmware to perform graphics primitives (like the RA8875 cited above).

Your idea could work. You may find someone has written a VT100 emulator for the Pi, and you can access it from the Pyboard via a UART. You'd need to deal with the VT100 editing commands. How were you planning to interface a keyboard and (if required) mouse?
Peter Hinch

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Re: Large color LCD?

Post by engineer » Tue Jan 14, 2020 6:39 pm

Thanks! I should be able to find a suitable display using that controller.

I hadn't given much thought to the mouse/keyboard -- i figured there must be a skin available somewhere that has dual USB host ports, and if not I can make a board using the ones for arduino as a starting point. Now that I think about it, maybe that Pi zero could do that as well. Something to think about.

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Roberthh
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Re: Large color LCD?

Post by Roberthh » Tue Jan 14, 2020 9:27 pm

I found buydisplay.com a good source for displays. Good quality, many sizes.

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Re: Large color LCD?

Post by MostlyHarmless » Wed Jan 15, 2020 1:16 am

pythoncoder wrote:
Tue Jan 14, 2020 6:07 pm
Your idea could work. You may find someone has written a VT100 emulator for the Pi, and you can access it from the Pyboard via a UART. You'd need to deal with the VT100 editing commands.
Oh ... you are thinking of emulating a full VT100 via UART? With all of the functionality described in termcap?

I had a real VT100 at home once, and although this has sentimental value, I probably won't want one again.

But then again, there is a market for Retro Arcade Cabinets, so maybe a Retro VT100 is something people would buy.

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Re: Large color LCD?

Post by pythoncoder » Wed Jan 15, 2020 6:40 am

you are thinking of emulating a full VT100 via UART?
If you want to do remote editing via a serial link you need some kind of protocol to handle operations such as delete, backspace, cursor moves and suchlike. I believe that the VT100 protocol (or more likely subsets) is still regarded as a standard in this respect.
Now that I think about it, maybe that Pi zero could do that as well.
I don't understand your application, but on the face of it, it would seem simplest to do the editing on the Pi and communicate the resultant text to the Pyboard via a UART.
Peter Hinch

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Re: Large color LCD?

Post by engineer » Wed Jan 15, 2020 4:49 pm

Re "I don't understand your application, but on the face of it, it would seem simplest to do the editing on the Pi and communicate the resultant text to the Pyboard via a UART."

The basic idea (keyboard, mouse, and display) could be done with a Pi, or with a PC for that matter. But I don't just want a computer with a keyboard, mouse, and display. I want a pyboard (or some other low-cost board running run micropython on the bare metal) that has a keyboard, mouse, and display.

As far as the video goes, what I am seeing at https://docs.micropython.org/en/latest/ ... 160cr.html is pretty much exactly what I want as far as the video goes, but the 1.9" x 1.8" size of the lcd160cr is too small. I still haven't given up hope on finding something around 6-8" that basically does the same thing.

The other way would be to roll my own. I have a lot of experience making custom electronics and with assembly language programming (I am a python newbie, but I am learning) so I believe I could make a board that fits on top of the Pyboard and gives it 2 USBs for mouse and keyboard and a video output.

I have been doing some searching, and it looks like I can make a version of this arduino shield that plugs into a Pyboard:

https://github.com/techtoys/HDMI-Shield ... a8876_Lite

https://www.youtube.com/watch?v=MUeIY_gLn3c

If I decide to do this I would make it open hardware and software so anyone could make one.

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Re: Large color LCD?

Post by engineer » Wed Jan 15, 2020 10:40 pm

OK, it looks like I have a solution.

According to

https://github.com/micropython/micropyt ... duinoPlus2

The Netduino Plus 2 is basically the same as a pyboard but has more GPIO pins broken out, Ethernet, and an Arduino formfactor.

and according to

https://www.electronics-lab.com/arduino ... -monitors/

There is an HDMI-Shield in Arduino form factor that creates an HDMI output from an SPI control input.

and of course I can get a USB host shield at

http://shop.tkjelectronics.dk/product_i ... ucts_id=43

Remaining questions:

[1] According to https://www.wildernesslabs.co/Netduino there is are newer N3 Ethernet and N3 WiFi boards. Will Micropython run on those as well as the Netduino Plus 2?

[2] Can I find a USB host shield with two USB outputs so I don't have to add a small USB hub for the keyboard and mouse?

[3] After I get it all working, would is be feasible to duplicate the electronics and fit it on a single board that plugs into the top of a Pyboard?

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Re: Large color LCD?

Post by pythoncoder » Thu Jan 16, 2020 6:41 am

That HDMI shield looks like a very interesting piece of kit.

I notice it's based on an RA8876. I recently wrote a driver for the RA8875, and also ported my nano-GUI to it. It was an interesting experience as the RA8875 evidently has bugs. Reliably reading back screen data from it proved impossible, requiring me to modify the GUI so as not to require it. It was not an easy port for other reasons: the docs are less than transparent and I spent a good deal of time studying the work of other people, namely Adafruit (acknowledged in the code comments).

I also found that the SPI bus wouldn't work above about 5MHz; Adafruit had evidently found the same. This limits performance, especially if you want to render text in fonts other than the built-in one.

Note that I haven't looked at the RA8876 other than a quick glance so I don't know its detailed spec. You may find the task easier if you can find some working sourcecode.

On the face of it, it looks like a great piece of hardware if you can write a driver for it.
Peter Hinch

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Re: Large color LCD?

Post by pythoncoder » Thu Jan 16, 2020 8:12 am

The website of the supplier of that shield seems to be down :(

It looks like a serious piece of electronics design given all those twisted PCB traces. Timing must be mega critical.
Peter Hinch

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