Pi in a Dreamcast VMU Build - WIP

moosepr

@obsidianspider you can play and charge with the module. The zero and the tft won't draw much current, so it will play happy

The voltage will range from 4.2v to 3ish v as the li-po battery drains and the protection will then step in and stop battery damage. The pi seems happy down to about 2.8ish but I have not tested that myself

Doesn't the vmu have a piezo element in there for it's speaker? Bit like a birthday card? I have tested one of those straight from the pwm audio pin. It works, but it's quiet https://hackaday.io/project/20152-gameboy-zero-but-smaller/log/54847-piezo-and-pico-8

obsidianspider

@moosepr said in Pi in a Dreamcast VMU Build - WIP:

Doesn't the vmu have a piezo element in there for it's speaker? Bit like a birthday card? I have tested one of those straight from the pwm audio pin. It works, but it's quiet https://hackaday.io/project/20152-gameboy-zero-but-smaller/log/54847-piezo-and-pico-8

I'm pretty sure that's all it is. I am not looking for THX-quality sound, but something other than silence would be nice. Not needing another board or a clump of capacitors and resistors would be great too. This is more of a novelty than anything. This build and the Burger King Gameboy Color toy are going to be "just to do it" and the Gameboy Advance is intended to be one that I'll actually play for extended periods of time, so I want that one more full-featured.

moosepr

@obsidianspider well all the audio filter bit does is clean up some of the hiss from the pwm audio. The piezo elements are low enough quality to not need the filtering. you can sometimes hear a little bit of a hiss if your really close to it.

I had my GBz wired up with the smd Piezo and thought it was really really quiet. was having a quick play with pico-8 the other day and the missus could hear it from the other side of the room, so it cant be too bad :P

obsidianspider

@moosepr I'm still wondering how you use ABXY when it's essentially a second D pad. I guess you never need to run and jump at the same time. ;)

moosepr

@obsidianspider yeah it takes a bit of getting used to. Maybe i need to make a slightly bigger version with actual buttons instead

obsidianspider

@moosepr I'm still curious what your latest creation will be. I was also looking around for another SPI-based screen to fit in the Burger King Gameboy Color, but I think the 2" Adafruit TV that I have is going to be my best option. Plus, I already spent the $40 on it. It fits perfectly inside the case.

I got confirmation emails this morning that my VMUs have shipped from Florida and that my screens have shipped from Shenzhen, China. C'mon little screens, you know you want to get here before the VMUs. You can do it!

Here's a nice teardown of a VMU on iFixit

Also, Sega Retro has a ton of great information about them including these specifications:

Technical Specifications

CPU: Sanyo LC86K87 (8-bit CPU, energy saving)[4]

Memory: 128 KB (200 blocks)

Power source: Two CR2032 batteries with auto-off function[4]

Display: 48 dot Width x 32 dot Height resolution,[4] Monochrome

Display size: 37 mm (1.46 inches) Width x 26 mm (1.02 inches) Height

Case dimensions: 47 mm (1.85 inches) Width x 80 mm (3.15 inches) Height x 16 *mm (0.63 inches) Depth

Sound: PWM sound chip,[4] 1-channel PWM sound source

Weight: 45g (0.099 pounds)

moosepr

@obsidianspider there are lots of options on aliexpress if you are willing to experiment

there is a 1.8" version of the ili9163
https://www.aliexpress.com/item/1-8-inch-15PIN-65K-TFT-LCD-Screen-ILI9163C-Drive-IC-SPI-Serial-Interface-128-160/32376372723.html

and a 2" screen with a random driver
https://www.aliexpress.com/item/2-0-inch-29PIN-TFT-LCD-Screen-SPFD54126B-LGDP4524-Drive-IC-176-RGB-220-8-16Bit/32301355935.html

to be fair, my project is not to dissimilar to yours. apparently my boards are set to be made on the 31st of march so i might have to keep you waiting till easter....

ABrugsch

@obsidianspider just so you know, those 1.44" screens are pretty much a perfect fit. there's a tiny bit of vertical space you'll need to make in the aperture to get all of the visible area visible and IIRC it needs to go with the ribbon at the top. As moose said elsewhere (one of the threads on Sudo IIRC) there's a couple of passives on the PCB but essentially you can ditch the carrier PCB.
I'm just looking for a battery that'll be suitable now but pretty much 500mAh is likely to fine if moose's measurements were correct, but have you seen that pi zero w handheld terminal video by N-O-D-E on youtube? he's got a 1500mAH battery that's a 752080 (80mmx20mmx7.5mm) that might just fit...

The charge board I linked to on the other thread prevents charging and use at the same time by having the 2 ports right next to each other... will be interesting to see what happens when I remove that block ;)

obsidianspider

@ABrugsch Yeah, I really don't want to have the battery hanging out the back of the case like in the prototype video, but he's also using a separate display driver board and a PowerBoost 500C, so that's taking up more room.

moosepr

yeah i recon even with a zero W in the mix, your 500mah battery should get you 2 hours, maybe more. It might alter depending on how efficient that boost board is.

you can run that screen with just the one passive!! and thats the 10 ohm resistor for the backlight. if you want to be really gheto, you can even chop out that resistor, although the backlight gains a blue tint because the led's are being run too hard, so im going to guess they wouldnt last too long.

the only problem i can see with having the cable/chip at the top, is the screens are designed to be used with the cable/chip at the bottom, so you might run into some weird visual issues with "colour inversion" as these cheep screens have poor viewing angles

obsidianspider

@moosepr Your imgur album showed that with the rotate set to 0 the image was "upside down", which is how I'd want it. How did that look "in real life"?

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Also, what theme is that? The huge consoles in the background looks great!

I'm kind of enjoying the "How few components can I use and still have all of this work?" aspect of this build. The Burger King build will need 5V due to the screen, otherwise I'd attempt to make that one run right off the lipo as well.

obsidianspider

This video is using an Arduino to drive the display, but even "upside down" the colors look really good. (Jump to 3:04, the forum doesn't support time stamps in video embeds.)

Here's another "upside down" video (Jump to 2:15)

moosepr

@obsidianspider try it straight from the li-po :P most things are pretty tollerant. apparently the pi only really needs the 5v to feed to the usb for external bits, but most memory sticks and wifi dongles dont really care if its 5v or less.

i will see if i can get some snaps of the colour inversion. it might not be as bad as i though.

the theme is made by @tronkyfran on this here forum. it is in the themes list built in to retropie as "tronkyfran" some of his artwork is awesome!! have a look here
https://retropie.org.uk/forum/topic/720/background-images-coming-back

ABrugsch

@moosepr doesn't the pi display a spark in the corner when the supply voltage drops below 5v? or is that just full size ones?

moosepr

@ABrugsch i get that on my pi3, but have never noticed it on the zero. I think you can actually turn the power/voltage warnings off

As usual you can override the behaviour in config.txt if you understand the risks: avoid_warnings=1 removes the warning overlay. avoid_warnings=2 additionally allows turbo when low-voltage is present.

https://www.raspberrypi.org/forums/viewtopic.php?t=82373

obsidianspider

I decided to order some of those cheap charging boards. 10 for $4.58, including shipping. (How are they making any money on this stuff?!) They're coming from China too, but since I have to wait for my screens anyway, I might as well save a few dollars. Do I need ten? No, but for the price, if I ever build something else that needs a charger, I'll have it, and won't have to wait another month.

(Photo from eBay auction)

moosepr

@obsidianspider yeah they are handy to have around. The circuit is really simple on those, I did consider embedding one onto my GBz board, but the pricing is to good not to take advantage of those boards. They must be knocking them out by the million!

moosepr

@obsidianspider here is what I mean about the screen inversion

https://twitter.com/Pi0CKET/status/846422958964924416

With the chip at the top, you're kinda in the middle of the bad zone

obsidianspider

@moosepr I see what you mean. I guess I'll have to take a look at how things line up, but I plan on looking at it face-on anyway. Not to mention that you said that rotating things 180 degrees would have that weird chunk of the screen blank anyway.

moosepr

@obsidianspider yeah im working on that!! apparently its a known issue. going to have a play with the st7735 driver and see if i can make it work 128x128

https://github.com/notro/fbtft/issues/453