Dashbord with 4 gauges from 4 displays

[clarkwinkelmann]

I'm building a car dashboard with 4 gauges and I'd like to use a Raspberry PI to render them from a single wide web page. Each gauge would be an LCD or OLED display with a resolution of at least 200x200 pixels. I have not bought anything so far, I'm trying to find whether that's possible at all.

dashboard_pi.png (65.78 KiB) Viewed 219 times

Each gauge is 11cm in diameter and there are a few cm of space between them. Between the first and second gauge there's a larger gap and there's the steering column in the way preventing me from using a single display across the whole dashboard. Except from that, the screens can be larger than the gauge if needed, or span across the 3 right-most gauges. There is a plastic piece covering any overflow.

From my research it's not possible to plug 4 such separate displays into the Pi. What I'm looking for is ideally a hardware solution that would let me use 4 separate square-ish SPI displays, and make them appear like a single large display to the Pi.

My solution A would be to use 4 identical displays. Solution B would be to use a small display for the first gauge, then have a single wide display for the last 3. I would prefer solution A as I could use the exact same display for each gauge instead of mixing potentially different screen types and pixel densities. I'm also not sure I found be able to find a display whose dimensions match solution B. For either of these solutions however, I'm unsure how to connect them to the Pi as a single large screen.

I have not decided on a final screen resolution yet. In my mockup I use 200x200 pixels for each gauge as an example but that's not a requirement. I could go higher or lower depending on what the hardware solution or Pi supports. I mention SPI as it's what I've been looking into but another way of connecting the displays to the Pi is also fine.

If there are some portions of the screens that aren't actually visible, I'd account for that in the webpage that generates the graphics. All I need is a way to have a single fullscreen webpage with each gauge showing a different part of it. I can account for all margins and overflows from the webpage.

I haven't been able to find any useful information on this on the internet. Does such a 4-SPI-to-1 hardware adapter exists? I know this exists for HDMI screens as I saw it in the past but I can't find a name for that product. Or can this be done in software? Or maybe there exists a display product that's sold as an assembly of 4 screens out of the box? For example a product that's designed as a cube with 4 screens on the outside that I could disassemble to get the 4-part display.

I have found multiple threads about "video walls" but those solutions seem to be about large screens. I have a limited amount of space and power here and I just can't fit 4 Raspberry Pi behind that dashboard and networking them together. I'm sure there should be a more power-efficient way of extending a video output across 4 small displays that doesn't require one computer per display.

All searches related to "screen split" seem to lead to either questions about dual screens on Pi for desktop applications, questions about cloning an image across multiple screens, or questions about connecting displays that can be controlled individually to display data from different sources.

Thanks for your help

[aBUGSworstnightmare]

Us3 two displays, a smalk one and a rectangular one.

I.e. Rhis 12.3in has the same height as a 7in display
viewtopic.php?f=45&t=157109&hilit=Lvds4pi#p1025223:-)

look for display which similiar pixel size to have the left gauge look/size similiar to the others.

[clarkwinkelmann]

Thanks!

I have now taken the dashboard apart and I found out that even borderless rectangular screens wouldn't actually fit in the two left-most gauges, so I would have to go with a rounded display for at least those. This kind of kills the possibility of using a single display for the 3 right gauges

Here's what it looks like (it's a Pontiac Firebird 3rd gen dashboard):

IMG_20200821_002740_cropped.jpg (120.54 KiB) Viewed 128 times

After a lot of time spent on Alibaba I found these "HDMI to MIPI DSI Board TC358870 Dual" boards which seem to support connecting two displays to one HDMI driver, with a switch to toggle between mirroring and expending. One of those is https://www.alibaba.com/product-detail/ ... 39406.html I have unfortunately not found any kit with the correct display size yet, but I expect some of the 4-to-5 inches round screens should work with the same board.

So my plan now would be to have two of those dual HDMI drivers, so I can feed 4 round screens from the two HDMI outputs of one Raspberry Pi 4.

The challenge now is finding compatible round screens of 4.3 to 4.5 inches with minimal borders, because I'm not sure I will be able to fit larger ones in there at all. But I'm hopeful, since there seem to be multiple Chinese screens made for bedroom table clocks of roughly the size I need.

I'll keep the thread updated with my findings.

[thagrol]

Appologies if you've already considered this but it looks like some of the gauges you want to replace are safety critical.

• Check local roadworthiness regulations.
• Check requirements for instrument accuracy (especially for things like speedometer and odometer)
• Check the impact to your car insurance. Most insurers will increase premiums if the car has been modified. Failure to inform them will likely invalidate your insurance.
• Pi do not boot instantly. It may be a couple of minurtes before your instruments are online.
• SD cards are not the most robust of storage devices. If yours fails you'll have no instruments.

Plus all the other issues with running a PI in an electically noisy environment and acheieving clean shutdowns.

[clarkwinkelmann]

Thanks, yes I have considered those. I'll still do multiple tests before committing to this new dashboard.

This is not the only modification to this car. It's actually being converted to an electric powertrain so most of those gauges would have no usage in the new car anyway. A full re-certification and new insurance will be needed in any case.

The left gauge is the only one that could be left untouched since I'll still need speedometer+odometer. My plan is to keep the original circuit board + counter behind the screen and relay the data to the PI, that way I still have a reliable odometer but can create a new unified dashboard with 4 screens and can afford loosing data on the PI.

Everything I plan to modify should match regulations (Switzerland).

The boot/shutdown part I still need to investigate to find out exactly how long it takes. I'll try to boot the PI as soon as doors open or car unlocks and I will install some proper shutdown + power cut. I might keep the PI running or sleeping under some circumstances, like if the vehicle is plugged in to a charger.

Thanks for the tips!

[PhatFil]

have you looked at the nextion displays from itead? my only experience is via youtube vids.. but they look like stand alone 'smart' screens that can talk via a serial connection.. so hooking 4x or more upto a pi via usb/ftdi, ttl,uart shouldnt be too tricky. not round tho..