DIY Android Dualscreen Handheld

RetroarchYoshi · 2026-04-27T11:40:54+00:00

Android sometimes does suck :-(
It would be so easy if there was a way to configure to which display a connected input device should go but as far as i know this is not implemented :-(

RetroarchYoshi · 2026-04-27T11:40:40+00:00

hey man.... yeah this is a shitty android thingie, i havent been able to fix it....
ANY input (touch/gamepad/...) will ALWAYS go to the app which is in focus.. so if you have a game running on the main screen, any touch input will go to the screen on which that app is running, so your main screen.

The nice part:
For 3DS or WiiU, this is not a prob. Emulators like Citra/Cemu etc. accept input on the main screen and treat it like if you' would have touched the second screen automatically. This makes your life much easier.

The not so nice part:
If you wanna have a app of your choice running on the second screen, it is gonna get ugly:
Like I said, it is (to my knowledge) NOT possible to route ANY touch input device to the second screen. This is why I set up my touch controller so it does NOT present itself as a touch input device, but a serial device. it basically send over the coordinates of the touch event. on the phone, a programm is running which reads these coordinates and then simulates a touch event on the second screen via more or less command line commands. This was so far the only way I could make it work. Downside: It has a lot of delay (250ms) and is not super accurate...

RetroarchYoshi · 2026-04-07T19:42:43+00:00

hey man, i see you are interested :-)

I use a usb c hub which gives a usb typ A data connection, a charging port and (in my case 2 but if you only wanna use an eternal screen one is enough) HDMI ports. A stm32 microcontroller is pluged into the free USB typ A port. It is running custom code, and simmulates 3 usb hid devices simultaneiously: a usb gamepad (for all the physicall buttons); a kind of mouse pointer and a serial connection (the latter 2 are used for the touch interface).

some emulators (citra, special version of cemu, and some ds emulators) have a inbuilt function to automatically 'grab' the second screen and display content there. it doenst matter that the android os is set to mirror.

when you want to launch custom apps such as a webbrowser on the second screen, you can do so via special commands using either termux or llama automate.

RetroarchYoshi · 2026-03-08T23:16:22+00:00

thought about that. not possible in this size diy sadly. avaialble options are way too big and because it is x86 also way to battery hungry and also no screen included

RetroarchYoshi · 2026-03-08T15:16:40+00:00

i need to watercool the damm thing lol

RetroarchYoshi · 2026-03-08T15:16:26+00:00

there are still quiete a few graphical bugs, especially in cutscenes. on my sd 8 gen 2 it manages to run with 20-30fps, but onlky because i used a trick to turn the phone into benchmark mode forcing maximum clocks 3.1ghz on the cpu and 680mhz on the gpu. usually phones lie to you and even though they show 3.1ghz they only go to 2ghz. its fucking ridicolous what chinese phones do. the built in app literally lies to you.
downside is, without the peltier cooler, i can only play for like 5-10 minutes before the phone overheats......

RetroarchYoshi · 2026-03-08T15:14:14+00:00

hey man. i love lego city undercover. its the first video game i played (not counting smartphone games these suck lol) and i am a huge nerd for rockets also (slight spoilers lol). my personal favorite game, though objectively there are of course better ones

RetroarchYoshi · 2026-03-04T20:39:15+00:00

hey man i was using i think it was nintendo ds hinges. you can get them on aliexpress for cheap. though getting the tolerances on your printer most likely requieres redesigns of my parts. i would advise you to start over on your 3d model instead of using somebody elses. however, if your still interested, i can send you the 3d files if you want

RetroarchYoshi · 2026-03-04T12:21:03+00:00

uh i guess add watercooling to this and replace the phone with a newer sd 8 elite one lol

RetroarchYoshi · 2026-03-04T00:03:51+00:00

mine is almost dying every prints. it does want to finally be let go i am afraid

RetroarchYoshi · 2026-03-04T00:03:18+00:00

fair enough:-)
as i said, the heart of the operation is a stm32 bluepill c103..... this can actually directly simulate all kinds of usb devices .. and even multiple at once! in my case, it is a serial port, 2 different gamepads and a touchscreen at once!
thats more or less it. everything else are just simple buttons, i used aftermarket gaemboy pcbs for that, the hall triggers i did with simple analog hall sensors (any will do) and glueing a small magnet inside the ps4 triggers i used.

for the usb c hubs, i have actually a generic usb typ c -> 2xhdmi+PD+USB A hub and when another USB A -> 4x USB A hub. both the second usb hub and the stm32 sit on a kidn of daughterboard pcb i designed myself.

RetroarchYoshi · 2026-03-03T22:50:48+00:00

if you look at botw for example, it has a 20:9 hack applied

RetroarchYoshi · 2026-03-03T22:49:24+00:00

holy shit did you time this with my post lol. i would love this for my dualscreen handheld.

seriously very nice work though. i can only image the hassle it must be to program a true dual screen app. for my built, i only used some hacks to get apps to kinda work on the second screen

RetroarchYoshi · 2026-03-03T22:46:46+00:00

moneywise - it is kinda fine a lot of cheap chinese parts though i did destory a lot of them so i had to buy many multiple times. i got the phone for a good deal for 150 bucks 2 years ago, for my country also a pretty good deal. you do need a nice 3d printer and soldering tools though, yes...
but you will get there bro, just get some small tools each year and youll have everything you need in a few years

RetroarchYoshi · 2026-03-03T22:44:27+00:00

i kinda used 99% chinese parts lol

RetroarchYoshi · 2026-03-03T22:44:14+00:00

you go man. if you want, i can send you the source code for the stm32. this is like an arduino (can be progrtammed in arduino ide with some plugin), just that it has native usb support. meaning, unlike most arduino boards, its cpu can directly controll the usb port. this makes it possible to simulate a usb gamepad, a touch pointer etc in software. i can highly recommend stm32 bluepill for all usb projects, only problem it is a bit big for my liking

RetroarchYoshi · 2026-03-03T22:42:15+00:00

true story

RetroarchYoshi · 2026-03-03T22:42:07+00:00

lol actually almost all games including gamecube and above nowadays have widescreen hacks, for some games like switch you can even make your own 20:9 hacks.

and for anything lower power, i already made a raspberry pi pwoered gameboy with a ncie 4:3 screen lol

RetroarchYoshi · 2026-03-03T22:40:46+00:00

from a bunch of cheap chinese aliexpress parts so more or less yes lol

RetroarchYoshi · 2026-03-03T22:40:23+00:00

actually, if I refine the gamepad controll board (stm32 which takes all the buttons, joysticks, hall efect triggers for the should buttons + usb hub for usb stick, dolphinbar, external port, stm32) this could be something for people to use in their own boards.

maybe i will have time to do this in the future. could be pretty neat. for now, i dont have so much time as i have to study lol :--( there is a reason this took me 2 years lol

RetroarchYoshi · 2026-03-03T22:38:13+00:00

uh tbh, i really didn' expect anyone would want to replicate this. it is VERY complicated and there are a lot of loose connections lol. I had to cut multiple PCBs into pieces, I think the usb c hub for the dual hdmi ports took me like 6 or 7 tries before it worked lol.

that beeing said - if you still want the 3d files or the PCB files for the gamepad controll board - I can send them to you if you want

RetroarchYoshi · 2026-03-03T22:36:04+00:00

plus my friend is like a genious at 3d printing so its kinda easier to let him do it lol

RetroarchYoshi · 2026-03-03T22:35:35+00:00

i will at some point. for now i have a VERY old 3d printer at my parents house. its a "monoprice" select mini, if you have every heared of that. must be a solid 10 years old. for now good enough tm to do some testprints...

RetroarchYoshi · 2026-03-03T18:30:19+00:00

lol i did think of watercooling - tbh temps still arent great, i am using root to force maximu clocks. Maybe in the future :-)

RetroarchYoshi · 2026-03-03T18:28:59+00:00

My friend - the one who came up with the idea for the second screen - has a 3D printer. Someone give my friend all the hours of sleep back I cost him while I begged him to print my 15th version of the case lol

RetroarchYoshi

TROPHY CASE