travistrue2008
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Hardware Interface for LCD

Tue Feb 13, 2018 12:27 pm

I found this LCD on Alibaba: https://wholesaler.alibaba.com/product- ... 45761.html

I'd like to hook it up to a Pi Zero. The LCD comes with a ribbon cable coming from its driver board as normal, but since the Pi Zero lacks a DSI port, I'll have to solder some jumper wires from the ribbon cable to the Pi Zero's GPIOs. I've seen examples of this online, but those were with other displays. How do I figure out how to go about this?

The product description says its interface input is this: "Digital 24-bit RGB/SERIAL/ RGB/CCIR656/CCIR601", and I'm not sure what to make of that. For starters, it looks like it's a 24-bit RGB display. Every other 3.5" TFT I've found on Alibaba is 16-bit color, so could that 24-bit figure be referring to something else?

A quick Google search reveals that CCIR 601 / 656 appears to be a type of video signal standard. Does this mean that the LCD expects me to send the data in an encoded format instead of raw RGB? I see that it's serial, but is there any way to determine which kind of serial protocol I have implement to send this (possibly encoded) data?
Sic parvis magna.

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mahjongg
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Re: Hardware Interface for LCD

Tue Feb 13, 2018 1:36 pm

This one won't work without a dedicated LCD driver.
It might work with the VGA/LCD driver built into the PI's SoC, using the same method Gerts VGA666 adapter works.

viewtopic.php?f=91&t=94424

aBUGSworstnightmare
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Re: Hardware Interface for LCD

Tue Feb 13, 2018 2:05 pm

Ai page mentions 24-bit RGB Interface --> you can connect it to Raspberry GPIO configured for DPI Interface.
But: you need to have the data sheet! Anyhow ... shipping cost are extraordinary high! So this is by far not a cheap 3.5in LCD.

You should look for something like this i.e. https://www.pollin.de/p/lcd-modul-et043 ... 272-121498

travistrue2008
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Re: Hardware Interface for LCD

Tue Feb 13, 2018 5:25 pm

Nice! The shipping price seems outrageous, but I always contact the sellers directly to get a direct quote on pricing. Information such as unit price and MOQ in the product search results page sometimes don't match up with the product description page in Alibaba for some reason...

I checked out the display, and it was nice! It looks like it could be a replacement screen for the PSP. I need a 4:3 version, so I found this:
https://www.pollin.de/p/lcd-modul-mit-t ... 03a-120817

Now, if this works, and I can run it via DPI, can I still get audio to work through the GPIO, or is that not possible since DPI uses those pins as well? I looked for solutions, and didn't find a definite answer, so I thought I'd ask.
Sic parvis magna.

aBUGSworstnightmare
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Re: Hardware Interface for LCD

Tue Feb 13, 2018 6:57 pm

Well, would not recommend that as you can't use it on the DPI interface.

5.7in : https://www.pollin.de/p/tft-display-thg ... 480-121402

travistrue2008
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Re: Hardware Interface for LCD

Wed Feb 14, 2018 1:43 am

I checked out that display, and it looks great! I looked at the specs, but it didn't specify if it was a 16-bit display or a 24-bit one. If it is a 16-bit display, then it sounds like I have two options (with trade-offs):
1) Buy a 24-bit display that's cheaper, but I have to hook it up to 20 GPIOs, lose PWM for audio, might have to buy other breakout boards, and work around its potential non-3.3V voltage requirements.
2) Buy a 16-bit display that side-steps all of the disadvantages, but it's more expensive, and I'm confined to a 16-bit colorspace.

Does that sound about right?
Sic parvis magna.

aBUGSworstnightmare
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Re: Hardware Interface for LCD

Wed Feb 14, 2018 11:56 am

5.7in Kyocera is 6bit color = 18bit, 3.3v (spec is available from the product page - First link).
DPI will always consume all/nearly all GPIO!

https://www.pollin.de/productdownloads/D121402D.PDF

travistrue2008
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Re: Hardware Interface for LCD

Wed Feb 14, 2018 11:51 pm

Thanks! I'll keep that in mind. 6-bit could be a nice tradeoff. I think an 18-bit DPI config would free up those PWM pins.
Sic parvis magna.

aBUGSworstnightmare
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Re: Hardware Interface for LCD

Thu Feb 15, 2018 8:12 am

travistrue2008 wrote: Thanks! I'll keep that in mind. 6-bit could be a nice tradeoff. I think an 18-bit DPI config would free up those PWM pins.
GPIO18/19 is unused when configuring (connecting) Display in dpi_output_format mode 6 (https://www.raspberrypi.org/documentati ... /README.md)
18-bit RGB gives you 256k colors

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