Everything Else

I've been meaning to make myself a Raspberry Pi handheld, but the designs I've seen on the web so far appear a bit impractical to me. I don't think I would actually be able to use something this top heavy/fat:



Or lacking a keyboard:



Or with a tiny screen, a BOM approaching $100, involving too much work:



http://n-o-d-e.net/post/107977286006/how-to-create-a-handheld-linux-terminal

My approach was much cheaper and lazier. I figured I'd eventually find a used/broken portable DVD player with a working screen that could be hollowed out by removing the DVD/CD drive. I would then place a compact keyboard in the cavity. Something like this:



While at a used electronics store, I picked up a pretty good candidate case/LCD combo in the form of a Philips portable DVD player. It was a model PD700, from the "for parts" bin, for a whopping $10. It looked ok, but was missing a power adapter. Here is what a new one looks like:



It didn't have a composite input, but I figured it was worth a shot. Often, the external jack isn't actually soldered on, but these generic DVD player motherboards still have the relevant pads available on the board. If that didn't turn out to be the case, maybe there would be a composite signal somewhere on the board I could get to. Worth an attempt.

So, once back in the garage, I opened it up and found that the motherboard - sadly - didn't have composite out pads. That would have been too easy. Couldn't really trace a usable signal of any sort. The LCD jumper appeared to have R, G and B lines but mixed in with a bunch of fairly complex timing/sync signals. Not something easily tappable. At least for me. Here is what the board looks like:



The chip right next to the connector that interfaces the DVD mechanism just seemed like it was a motor driver. The giveaways were the thicker pins, location on the board... I didn't bother to google it. But the large chip in the center of the board turned out to be interesting; a Sunplus 8202P, which is a RISC based MPEG decoder/all-in-one solution for portable DVD players. Couldn't find the datasheet for the 8202p, but here's the description of the 8202K from the Sunplus website:



And I also found the 8202S pinouts, here:



http://w3.sunplus.com/products/sphe8202k.asp

[For those interested in this chip, it turns out the source code for it is available online. I briefly browsed through it, but this could be potentially valuable for someone who wants to modify the source with custom features. Here's the link:
http://en.pudn.com/downloads386/sourcec ... 24_en.html ]

I figured, ok, the LCD's obviously being driven by the 8202, so if I isolate the pin delivering the signal, maybe I can piggyback my composite out from the Raspberry Pi and then kill the composite out from the 8202. To test this hypothesis I powered up the DVD player... it wouldn't power on. That explained the "for-parts" and $10 price tag. In order to debug, I was messing around with a multi-meter and realized that the system would start up only if the PSU experienced a momentary short-circuit. So, that solved that problem and the DVD player "booted up".

Post boot, I saw the Philips logo and the menu items were working fine! The LCD was actually pretty decent looking so I figured this would make for a nice handheld display.

Next step was to identify some candidate pins... I got the raspberry pi running, and then soldered a couple of probes to the composite out pads on the Pi. I placed these probes on the incredibly narrow and tightly packaged 8202 pins, including the TV_DAC lines and the promisingly named V_COMP line. For a few seconds, I saw the raspberry pi command line appear, very fuzzily, over the Philips DVD menu, in B&W. I got excited and as I was trying the other TV_DAC pins, the probe with the composite signal touched a pin it shouldn't have. I don't know which one. But there's several 3.3V lines in close proximity, as well as bias voltages.

Net-net, after seeing the shell command prompt text appear for a bit, the LCD blanked out and all I could see was a white background with random colored lines. I rebooted the DVD player, tried several times to get it to just show the menu, but no. It was fried. Specifically, "it" probably being the 8202. Damn.

But that wasn't enough, apparently. When I tried connecting the Rpi to another composite monitor, it wouldn't display anything. Yet, I could see the SD card activity LED flash on power-up, so I knew it was working. I tried an HDMI to VGA adapter and, sure enough, the HDMI out still worked. Apparently the Composite out on the Pi had also died.

What I discovered next was probably the worst part of the screw-up. The USB ports on the Pi wouldn't work either. A cryptic power message appears on boot, followed by enumeration errors. I tried a powered hub, wired keyboards of a variety of types, a USB Wifi adapter... nothing works.



What a chain of failures! So I figured, ok, the board still boots, it has an HDMI display. If USB is fried, maybe I can connect to Ethernet (wired) and SSH into it. But no. Ethernet is dead too.

So, the conclusion of this sad tale is that I am back where I started. Two hours, a cheap DVD player and a Raspberry Pi were the casualties in this - on hindsight, perhaps ill-advised - experiment. That said, the LCD itself might still work if I can find a driver board. And the plastic housing of the DVD player is a pretty good option for whenever I regain the courage to try this again.

I haven't understood what is your will, what do you want to obtain ? a PDA ?
Why don't you buy a japanese one instead of building one ?

ivelegacy wrote: I haven't understood what is your will, what do you want to obtain ? a PDA ?

A Raspberry Pi based handheld running Linux.

Why don't you buy a japanese one instead of building one ?

Because it's fun. Since you are participating on a forum where folks derive their enjoyment from resurrecting 25+ year old hardware and porting software to these systems, I am astonished you would expect much in the way of build-vs-buy pragmatism

Maybe try one of the smallish 8-10" TFT monitors, many of which have USB or serial touchscreens. You would have to bolt on a beefy enough battery as most of them aren't exactly designed for energy efficiency, but in keeping with the DIY spirit I expect you would want it to be fairly chunky anyways. Otherwise people will just think it is an ipad. You could 3d-print a thicker back panel to hide the pi and battery, and design some sort of attachment to a keyboard.

Maybe something like this would be a better starting point?

edit: don't know why this URL isn't showing up so I will put it in code blocks...

what do you think about the design of Apple Newton ? The LCD is ~ 5" 16:9, there is enough space inside, and let me say, an external keyboard is better (in ergonomics terms) than both other solutions: QWERTY on screen and femto keyboards.

of course you could hack an existing device, but I also think the Newton's design could be customized using a 3D printers (STL models)

guardian452 wrote: Maybe try one of the smallish 8-10" TFT monitors, many of which have USB or serial touchscreens. You would have to bolt on a beefy enough battery as most of them aren't exactly designed for energy efficiency, but in keeping with the DIY spirit I expect you would want it to be fairly chunky anyways. Otherwise people will just think it is an ipad. You could 3d-print a thicker back panel to hide the pi and battery, and design some sort of attachment to a keyboard.

Maybe something like this would be a better starting point?

edit: don't know why this URL isn't showing up so I will put it in code blocks...

Code: Select all

http://www.amazon.com/Tontec%C2%AE-Resolution-Raspberry-Rearview-Headrest/dp/B00OOJPAGW/ref=sr_1_1?s=electronics&ie=UTF8&qid=1437945195&sr=1-1&keywords=tft+lcd+hdmi

Thanks for the link, and that's a good idea. There are actually a lot of alternate LCD choices, meant primarily as backup camera displays for cars, that have a composite in. I was going for the DVD player simply because the casing is already perfectly adapted for the LCD it houses. That said, LCD driver boards with a proper composite or hdmi in are a much safer bet. I'll just have to engineer a case from scratch...

Apple Newton's design

I'm quite baffled how the heck you managed to blow so many components.

pentium wrote: I'm quite baffled how the heck you managed to blow so many components.

I'm equally baffled. It literally happened in under a second. Obviously the probe slipped and touched some other pin. But there were no physical signs of damage on either board. I initially thought I'd just got the system in a weird, unstable state. But after many reboots on both systems, it turned out to be otherwise.

ivelegacy wrote:
Apple Newton's design

I like how the Newton looks, but I am trying to get a keyboard in there. I really took to the blackberry physical keyboards back when blackberry was still a thing...

well, blackberry makes the 'passport' which still comes with a keyboard. of course it is entirely up to debate if blackberry is still 'a thing'.
i was fond of these for quite a while, too but nowadays i find touchscreen-based ones to work better. no crammed together buttons anymore and when you don't need a keyboard, it just conveniently fades out of the way.

Since the end of the jurassic Zaurus (PDAs made by Sharp in Japan, gentoo runs on my Akita), I have been thinking for designing something cool, actually I had the light bulb shining in my head: what about a gear inside a plexiglass tube ? LCD support ? who cares, trasparente tube, simple design, nobody has to care. Oh, external wifi keyboard, internal battery pack.

Sooner or later I will build it

GIJoe wrote: well, blackberry makes the 'passport' which still comes with a keyboard. of course it is entirely up to debate if blackberry is still 'a thing'.

I've had an interesting and somewhat complex history with BlackBerry, which goes considerably beyond being a user of their products. Based on those experiences, I can certainly attest to the fact that they truly oozed thingness at one time. Sadly, and I mean this when I say it, not so much anymore. For those interested in BB, I recently got copies of two books, written 5 years apart, that discuss RIM's evolution and eventual tribulations. The books are, "BlackBerry: The Inside Story of Research in Motion" and "Losing the signal' - I have not read them yet, but leafing through them, they appear quite interesting.

GIJoe wrote: i was fond of these for quite a while, too but nowadays i find touchscreen-based ones to work better. no crammed together buttons anymore and when you don't need a keyboard, it just conveniently fades out of the way.

True. I would do a touchscreen, but resistive touchscreens are truly miserable to use, and capacitive overlays are quite pricey. If you remember a pre-netbook handheld computer company called oqo, and their rival, flipstart, that's kind of what I am going for. The flipstart more so, to be specific. Here's what it looks like:

i don't remember this company or product specifically, no. but a mate in uni used to have small computers running some sort of cut-down/mobile version of windows in the form factor of a small netbook around '97/'98. perhaps something in-betweeen a small laptop and an early nokia communicator, widescreen i think. these were a 'thing', too, for a brief period at least.

There were a lot of Handheld PCs running Windows CE on MIPS/SuperH/ARM, an actual RTOS that looked suspiciously like Windows. It even had a cut down Win32 it used to run cut down Office and IE. Made by a bunch of companies, like HP, Sharp, Compaq, NEC, Ericsson, etc. They're neat, but Pocket PCs are easier to find.

sgifanatic wrote: Because it's fun. Since you are participating on a forum where folks derive their enjoyment from resurrecting 25+ year old hardware and porting software to these systems, I am astonished you would expect much in the way of build-vs-buy pragmatism

Maybe take a look at the Neo900 ?

I was real happy with the N900 physically. And some of the software was pretty neat, but overall it is a pos. Full control over the device without that maemo garbage might make it into what it could have been.

hamei wrote: Maybe take a look at the Neo900 ?

Thank you for that info. I wasn't aware of this project. Glancing briefly through the specs/design, it certainly looks interesting.

And I did look at it in more detail. Interesting, but 1100-1200 euros for a 1ghz/1gb system with a small screen doesn't quite fit with what I had in mind.

The Flipstart form factor, large screen and 1ghz x quad core performance at an affordable price point, i.e. 80-90% lower than the neo900, running Linux, is kind of what I am shooting for. But mine is just a hobby project. It certainly won't have the fit and finish of the neo900.

I talked about the plexiglass-tube-computer because it's compliant with the hobby's resources. I mean, easy to be built, cheap and funny to be used. I really think I will make one, putting a pretty 5inc 16:9 LCD in its inside, plus a pair of solar cells and LiPo batteries.

but more seriously, what do you think about recycling an EEE/PC mini laptop ? I have seen a few funny projects, guys built a portable C64.

sgifanatic wrote: And I did look at it in more detail. Interesting, but 1100-1200 euros for a 1ghz/1gb system with a small screen doesn't quite fit with what I had in mind.

Yeah, I saw the price increase

On the other hand, at some point in one's life items that actually work and will not be "deprecated" by next week gain value ... one gets sick and tired of changing all the electrical outlets in the house every month because some squid decided "hey ! let's make the prongs go the other way !"

If they don't have the problems the Nokia did (can't charge the battery ? Who thought that one up ?) then the price could be reasonable for a phone that you can actually make do what you want. Not something that fricking imbecile Jonny Ive thinks is kewl, d00d.