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King Dub Dub
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Dual Monitors With Raspberry Pi 3: Is It Possible?

Wed Oct 09, 2019 12:24 am

Heller everyone! I have been looking through the forums and the internet and can't seem to find a clear solution to my problem. I would like to have 2 monitors for the raspberry pi 3, preferably through RCA. I believe I will either have to use the HDMI and RCA ports already on the pi and convert the HDMI to RCA with an adapter, or somehow get another RCA output over the GPIO's. I am using this monocular: https://www.aliexpress.com/i/32832774163.html and an ancient screen from a soon-to-be-cannibalized car dvd player (it looks like this: https://www.walmart.com/ip/Venturer-Car ... rs/4756575 , but it's about 14 years old now and I only have the main hub player, the alternate display was destroyed). I have been considering buying a rpi 4 and converting the HDMI mini outputs to rca, but then I would need 2 adapters and that would be bulky and messy.

I plan on having the pi desktop visible through the monocular and a pygame window running on the larger TV monitor.

Is this feasible or am I just being an idiot? Will I need to buy a rpi 4? Thank you for reading this post, please reply if you have any thoughts that may help!
Heller people in the future! This is past King Dub Dub reminding future King Dub Dub not to say anything stupid. I apologize for anything stupid that future-me says.

6by9
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Wed Oct 09, 2019 6:26 am

You can not use the HDMI and composite video output - they share one part of the display pipeline.
You can have HDMI + DPI, or HDMI + DSI (and probably AV + DPI or AV + DSI, but I've not checked).

There are a number of DPI to analogue RGB cables available - the VGA666 is one aimed at analogue VGA monitors, but there is also the PiSCART for RGB on a SCART connector. It rather depends on exactly what your other monitor supports.
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rpdom
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Wed Oct 09, 2019 6:35 am

6by9 wrote:
Wed Oct 09, 2019 6:26 am
You can not use the HDMI and composite video output - they share one part of the display pipeline.
You can have HDMI + DPI, or HDMI + DSI (and probably AV + DPI or AV + DSI, but I've not checked).
I'm pretty certain I have used AV + DPI at one point. When I got my first Pi I didn't have anything that could handle HDMI. I had an RCA to VGA converter driving one monitor and the VGA-666 DPI board driving another and had videos playing on both with omxplayer. That was a Pi 1B, but should apply to the later models too.

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Gavinmc42
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Wed Oct 09, 2019 6:38 am

What about one HDMI and one composite on a Pi4?
Does the Pi4 share the same pipeline for both HDMI's?
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6by9
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Wed Oct 09, 2019 7:55 am

Gavinmc42 wrote:
Wed Oct 09, 2019 6:38 am
What about one HDMI and one composite on a Pi4?
Does the Pi4 share the same pipeline for both HDMI's?
In the standard configuration the vec and hdmi0 share an hvs channel. In theory you could run vec and hdmi1, but I seem to recall it got too complex on clock setup and enabling the vec disables all other displays.
The hdmi outputs can be routed through any of the hvs channels, but again it makes the setup endlessly more complex trying to assign outputs to channels.
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King Dub Dub
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Wed Oct 09, 2019 11:39 pm

Thank you all for replying so quickly, you've made it clear that HDMI is bad and it's better to stick with RCA/Composite and use something else besides HDMI as a secondary output. I have heard of ways to drive displays through the GPIO's before, could one drive RCA or outputs through them? I like the idea of using a DSI interface instead of the old TV monitor, but I still want to keep the monitor I have now as I have just finished configuring it's display for the Pi and I already have it ready to use. Is there a way to convert the DSI to RCA/Composite as well (I may use DSI for an upgrade in later on though)?
There are a number of DPI to analogue RGB cables available
What is this "DPI" you speak of? I have only heard it for DotsPerInch, or PPI, for measuring the resolution of displays. Did you mean DVI or is that a European display configuration?
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rpdom
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Thu Oct 10, 2019 3:15 am

King Dub Dub wrote:
Wed Oct 09, 2019 11:39 pm
What is this "DPI" you speak of?
Display Parallel Interface

It uses pretty much all of the GPIO pins to provide 6 bit R, G and B signals (24-bit total), plus sync signals. Gert van Loo designed a simple board that uses resistors to convert that to an analogue VGA compatible output (the VGA-666 board kit). Others (ABugsWorstNightmare, I believe) have designed other boards that will interface the DPI to some display panels without having to use an HDMI converter board.

caffeeq
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Re: Dual Monitors With Raspberry Pi 3: Is It Possible?

Mon Nov 18, 2019 10:49 pm

I'm interested in this topic as well, I'm working with the Raspberry Pi 3 b+ and I want to hook 2 displays up to it.

I have the official Raspberry Pi display which I believe should be a DPI display: https://www.amazon.com/Raspberry-Pi-7-T ... 458&sr=8-3

As well as the Landzo 7 inch display which is connected by HDMI:
https://www.amazon.com/gp/product/B01ID ... UTF8&psc=1

They both work individually but when I hook up both displays to the Raspberry Pi, only the official Raspberry Pi displays the screen and the HDMI display has a rainbow screensaver on it.

Is there some config.txt code that is necessary to have both displays on at the same time?

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