Looking for a squared USB-C display with specific dimension to replace the default display of the HackBerry Pi Zero.

[ziomario]

Hello boys.

I've bought and opened the Hackberry-Pi_Zero :

https://github.com/ZitaoTech/Hackberry-Pi_Zero

Let's give a look at the pictures below. This is how how the display (4" 720X720 TFT) is attached to the board (Raspberry Pi Zero) :

my idea is to remove that display and to use one USB-C display of the same inches. For example with this model :

https://www.waveshare.com/product/raspberry-pi/displays/3.5inch-hdmi-lcd-e.htm

I'm sure that in this case,FreeBSD will be able to boot and run. Anyway,I'm looking for a little bit better display because the original one that I want to remove is 4 inches. The new one is 3,5 inches and it's too short. There's some wasted "screen" space. I would like to find a display at least with the same inches,but that can replace perfectly the default one.

The dimensions of the default display is :

width = 7.5 cm
height = 8 cm

the new display should fit perfectly inside this frame :

I'm actively looking for a squared USB-C display that can match those dimensions. I will find it faster with your help. Thanks.

 

[S-TKUC]

There is too little information.
The requirements I understand at this point are as follows:

- Display area must be within a 75*80mm frame.

- Video interface is HDMI

- Touch control and power interface is USB Type-C (USB2.0)

Now, the base Hackberry-Pi_Zero seems to use GPIO for display control.
You are trying to replace this with HDMI.
At this point, you can see that there are many issues to be resolved.

---

First and foremost, it's best not to modify the interface as much as possible in order to take advantage of the base device.

The base product probably uses this display and communicates using the DPI666 method.
EDIT: DPI666 is also known as VGA666, you can refer to the article from 10 years ago.

GitHub - robertely/dpi666: Raw DPI for Raspberry-Pi B+

Raw DPI for Raspberry-Pi B+. Contribute to robertely/dpi666 development by creating an account on GitHub.

github.com

GitHub - 6by9/dpi666: Raw DPI for Raspberry-Pi B+

Raw DPI for Raspberry-Pi B+. Contribute to 6by9/dpi666 development by creating an account on GitHub.

github.com

https://raw.githubusercontent.com/fenlogic/vga666/master/documents/vga_manual.pdf

In other words, the ideal thing to do would be to learn the DPI666 implementation of display control via GPIO and make it run on FreeBSD.

---

As a second priority, you should consider SPI or MIPI-DSI, which are common display interfaces for small devices.
SPI is slow, but can communicate using three signal lines.
MIPI-DSI can display video at various resolutions and frame rates over a flat cable without having to worry about connection issues.

You should consider whether these can be run on FreeBSD.

---

I think the method you chose is the third priority.
Changing the display interface to HDMI would probably require minimal changes on the FreeBSD side...
But this change would create other problems.

HDMI was not designed for use in portable devices.
It would consume more battery power, would require more wires, and would require a thicker, larger case.
In other words, it would not take advantage of the product it is based on.

This is probably the case with this display, but I don't think it's a good idea.

 

[ziomario]

Depending on my low specific skills,this is the only doable idea :

This is probably the case with this display

unfortunately the size of that screen does not fit inside the frame,because it is 8.4 x 8.4 cm,while I have 7.5 cm x 8 cm. Anyway,that screen does not seem to be compact like this one :

https://it.aliexpress.com/item/1005006724749833.html

unfortunately it is 5 inches,too much. But you got the idea. Anyway I'm sure that somewhere there is a display like that that fit inside the frame of the HackBerry Pi. But it's not easy to find it.

This is nice :

https://www.amazon.it/Capacitivo-Laminazione-Completa-Quadrato-Raspberry/dp/B0BCPBRC3G

unfortunately it does not have the right size.

 

[S-TKUC]

Video output to GPIO in DPI666 format is a feature of the Raspberry Pi's built-in GPU, and it should work just by adding two lines to the config.
This is a hardware function and is not likely to be OS-dependent, but I have not tried it so I cannot be certain.

The display area is contained within the frame.

 

[ziomario]

Video output to GPIO in DPI666 format is a feature of the Raspberry Pi's built-in GPU, and it should work just by adding two lines to the config.
This is a hardware function and is not likely to be OS-dependent, but I have not tried it so I cannot be certain.

View attachment 391261
The display area is contained within the frame.

Judge by yourself if "your" display can match with the size of the frame :

Video output to GPIO in DPI666 format is a feature of the Raspberry Pi's built-in GPU, and it should work just by adding two lines to the config.
This is a hardware function and is not likely to be OS-dependent, but I have not tried it so I cannot be certain.

I could ask how to do that. But if I'm not sure that it will work,I will not buy that display. Because it is expensive and I'm out of money.

The display area is contained within the frame.

Give a look behind that display,you will find that it's not slim.

I doubt. The display area of "your" display seems to be 8.4,not 72.53. I don't understand why you exclude the black frame all around the display.

 

[S-TKUC]

I could ask how to do that. But if I'm not sure that it will work,I will not buy that display. Because it is expensive and I'm out of money.

If DPI666 works, you don't need to buy a display. This means you can use the Hackberry-Pi_Zero display you already have.

 

[ziomario]

If DPI666 works, you don't need to buy a display. This means you can use the Hackberry-Pi_Zero display you already have.

DPI666 does not fit inside the frame and it is not slim. And it does not work out of the box like the type/kind of display that I used for the tablet.
Using DPI666 there is an high chance to encounter a lot of troubles....that I can't manage. Usually is not easy as adding "two lines in a config file".

 

[S-TKUC]

As far as I can see from the schematics of Hackberry-Pi_Zero, it definitely uses DPI666.

If you successfully configure it with DPI666, you don't need to buy anything else.

It means that your existing Hackberry-Pi_Zero will function as a FreeBSD machine as is.

(Only if the RP2040 Raspberry Pi Pico coprocessor is driving the Blackberry keyboard as the standard keyboard device, which is probably the case.)

The base product probably uses this display and communicates using the DPI666 method.
EDIT: DPI666 is also known as VGA666, you can refer to the article from 10 years ago.

GitHub - robertely/dpi666: Raw DPI for Raspberry-Pi B+

Raw DPI for Raspberry-Pi B+. Contribute to robertely/dpi666 development by creating an account on GitHub.

github.com

GitHub - 6by9/dpi666: Raw DPI for Raspberry-Pi B+

Raw DPI for Raspberry-Pi B+. Contribute to 6by9/dpi666 development by creating an account on GitHub.

github.com

https://raw.githubusercontent.com/fenlogic/vga666/master/documents/vga_manual.pdf
In other words, the ideal thing to do would be to learn the DPI666 implementation of display control via GPIO and make it run on FreeBSD.

I introduced this display as an example of "what is DPI666?"

I just wanted to show that the display that comes with the Hackberry-Pi_Zero uses the same DPI666 communication interface.

This is a function provided by the hardware and is OS independent.

If you can write it in Config.txt, it should work exactly the same as outputting video to HDMI.

If there is an issue, it is that if you want to make the touch panel (pointing device) work, you will probably need to create a driver for FreeBSD...

But that is the same condition even if you buy an HDMI display.

 

[ziomario]

But that is the same condition even if you buy an HDMI display.

The display that I've bought for the tablet worked out of the box without writing in any config file. Wonderful. And I think the same will happen if I buy a display that uses the same technology.

The display used by the HackBerry PI does not work out of the box. And I suspect that it will not do it so easy. I imagine that I should make the debug of the reasons,but at this point I must enter inside one high technical territory where I don't have the mininum competence to stay.

 

[S-TKUC]

You're not getting the point across at all.

I said, "The conditions for touch panel operation are the same for HDMI and DPI666."

I didn't say, "The conditions for the difficulty of projecting images onto a display are the same for HDMI and DPI666."


If my explanation doesn't make sense I'll just stop explaining.

---

I'm not an expert on either Raspberry Pi or Linux.

I don't understand whether Config.txt is recorded on the Raspberry Pi when it is recognized (similar to the BIOS settings on a PC), or whether the Raspberry Pi OS (Linux) interprets and converts the contents of Config.txt and sends commands to the SoC.

In the former case, once you write the config in the Raspberry Pi environment, the changes should be retained even if you write a different OS to a different SD card and start it, and the image should be output in the DPI666 method.

In the latter case, you will need to figure out how to write it on the FreeBSD side, or understand the raw commands to the SoC and how to execute them.

EDIT:
After some research, I found that config.txt functions like a BIOS on a PC, but is placed on the same partition on the SD card as bootcode.bin and start.elf.
This file is loaded before the OS starts and configures the SoC.

This means that this file will always be present on the SD card and will function with FreeBSD as well.

All you need to do is edit /boot/config.txt on the SD card used to boot FreeBSD so that it has the same content as config.txt for Hackberry-Pi_Zero, at least once.

 

[ziomario]

After some research, I found that config.txt functions like a BIOS on a PC, but is placed on the same partition on the SD card as bootcode.bin and start.elf.
This file is loaded before the OS starts and configures the SoC.

This means that this file will always be present on the SD card and will function with FreeBSD as well.

All you need to do is edit /boot/config.txt on the SD card used to boot FreeBSD so that it has the same content as config.txt for Hackberry-Pi_Zero, at least once.

I know. I have this basic knowledge. But nothing more. I don't know how what to add inside the config.txt file. Probably there are much more modifications to do,such as the recompilation of the device tree,that by default is tailored for Linux,but it's not valid for FreeBSD.

I want to repeat that the easier and direct way is to find a display that has the hardware characteristics that I have mentioned before.

 

[S-TKUC]

Give a look behind that display,you will find that it's not slim.

I doubt. The display area of "your" display seems to be 8.4,not 72.53. I don't understand why you exclude the black frame all around the display.

One thing is certain.
If you buy an HDMI monitor, the exact same thing will happen, so this is a meaningless opinion.
An HDMI monitor would require a board to convert to HDMI and a thick connector, so it would never fit into the Hackberry-Pi_Zero case.

In other words, once you choose HDMI, the case will need to be redesigned.

At that point, there's no point in discussing subtle differences in display size.

You just need to make a case that will fit your newly chosen display.

Or rather, you can't move forward without making a case.

Conversely, you can choose the display you like without worrying about size.

 

[ziomario]

In other words, once you choose HDMI, the case will need to be redesigned.

You could do it,in 2/3 days based on your deep knowledge of CAD ; the case of the HackBerry Pi is a way less complicated than the tablet one.

You are not obliged. Maybe in the future I will find someone who wants or I could do it by myself ; I'm only considering this route easier than to get bogged me down in setting up something too complicated for me.

Maybe I can buy a case that's already been created for an existing phone. There are some routes to try to follow.

---> An HDMI monitor would require a board to convert to HDMI and a thick connector, so it would never fit into the Hackberry-Pi_Zero case.

Where is the board that you have mentioned,in this display :

8inch Capacitive Touch Display, Wide Color Gamut, 1280×800, Optical Bonding Toughened Glass Panel, HDMI/Type-C Display Interface, 10-Point Touch, Aluminum Alloy Case | 8HP-CAPLCD Monitor

8inch Capacitive Touch Display, Wide Color Gamut, 1280×800, Optical Bonding Toughened Glass Panel, HDMI/Type-C Display Interface, 10-Point Touch, Aluminum Alloy Case | 8HP-CAPLCD Monitor

www.waveshare.com

I don't see it externally...maybe it is internally ?

At this point,I think that a nice compromise is to grab a display like this :

https://it.aliexpress.com/item/1005006724749833.html

or this one :

https://it.aliexpress.com/item/1005008042586030.html

what do you think ? for sure it does not fit inside the case,so I should create a new one.