Intro: Raspberry Pi Tablet
This Christmas, my brother gave me a Raspberry Pi 2 and the official 7 inch touchscreen.
Wanting to make use of this great gift, I decided that it would make a great project for a little tablet.
While it is not quite finished yet, it still needs a new case (a little more care taken over the woodwork) a blob of sugru on the flick switch wire, and some better designed USB openings. I think i might make a small cover for the usb hole or something.
It is currently running Ubuntu MATE but as you can read in the next step, I tried other operating systems too...
Step 1: The OS
Initially we tried to install Plex, but we only wanted a client for viewing as my brother already had a Plex server. As there is no Plex client available for the raspberry pi, it was not really what we wanted. When I got back home, I tried running some other OS on the Pi. I had already made an arcade for my office (https://twitter.com/torquilharkness/status/630707434152153088), so have used the pimame OS before with great satisfaction, I also installed Raspbian, but the touchscreen and onscreen keyboard didn't perform as well as i hoped.
I also tried Jolla Sailfish (see attached video), but the official Raspberry pi wireless dongle was not detected and I could not be bothered searching for a solution.
After that i went with OSMC and was very happy with the interface. Although with OSMC the 'back' command is the keyboard 'Esc' button, there is no touch screen equivalent (or not that i know of yet, i haven't looked at creating a custom command).
Going back to Linux again as I wanted to try using it as a full computer, not just something to watch movies. Plus, the audio on a pi is awful for just plugging speakers/headphones in (more about that later).
The OS i went with is Ubuntu MATE. It is phenomenal. Really smooth. It does need some tweaking and a few updates. Plus the performance is a bit laggy sometimes. It would also benefit from a utility to overclock the pi like raspbian has. There is a way to do it manually, but it takes a lot of time and effort which I don't have. I installed a touchscreen keyboard that is much much better than the one i had on Raspbian, and the touchscreen on Ubuntu seems to just be a much nicer experience. Right now I am trying to get Kodi installed, because i do not want to swap the media card just to have OSMC running.
You can see from the attached video that a movie file plays really well in OMXPlayer. In VLC it is about one frame every 20 seconds, so there must be some config issues that i have not solved.
Once I was happy with the OS, I wanted to try to keep it all together in some sort of case and maybe buy a battery that i could make this set up a bit more mobile. On to the case build...
Step 2: The Build
So I started with just the screen, the Pi, and a really nice screen mount that my brother also gave me. https://shop.pimoroni.com/products/raspberry-pi-7-touchscreen-display-with-frame
The screen holder/stand is perspex and holds the screen really nicely. I could have removed it and maybe saved some space, but honestly, size is not an issue here and i like the support that the screen frame gives to the thin glass.
Apart from the obvious space saving that I was able to do, I am not a supporter of making everything a few millimeters smaller, only to end up sacrificing the battery life of whatever you are building. (Yes, i used to own a nokia 3300 and charged my phone once a week, and only if it needed a top up!) I would rather have my things a bit bigger, with more battery life.
The screen casing I have mounts the pi right in the middle. They do say
that you can mount it in a reverse position, but you need to solder the leads. I did mount it in the reverse position, but as it was a present, i did not want to start soldering on to it or messing about too much with it. So as i had a couple of spare leads, i heated up the plastic and bent two of them at 90 degrees. they fitted nicely.
As i had removed the screws that held the screen mount together, i added
some small brass screws and some metal plate to keep the screen mounting in place. I did not have anything fancy, just some builders metal strapping that i had used to build my chicken coup.
I wanted to make what I had, a little more mobile, so I decided to buy a battery from amazon. I had seen that some users on the forums of the touchscreen were using 10,000 mA/h batteries, I went with CoolReall 15600 mA/h and although it was a little bigger than i had hoped, the specs said that it was the same length as the screen, so i planned on just strapping it to the back. I was happy to go bigger, for the extra battery size.
For a couple of weeks, I just strapped the battery to the back with ductape and it sat at a nice angle. Not really a usable tablet, but I had used it for up to 8 hours on the first day, and the battery said it was still 50 percent charged. Until I can play movies on it, or stop fiddling with it, i wont know true battery (normal use conditions), times, but it is looking like at least a solid 12 hour use before it needs charged..
I decided to strip down the battery and see if i could rearrange the internals of the battery, simply because the width was about 5mm too wide to run alongside the pi board. So on to more details about the battery...
Step 3: The Battery
The battery bank that i bought had some nice features. https://www.amazon.es/gp/product/B012F0689E
You can charge it at the same time as running the pi. Although a note of caution, the unit switches all power off for a second when you initially plug it in to charge.
Also, there was a torch when you double click the button (not really useful to me, but i left it in place), and some battery status lights. I liked those and planned to use them in the build.
Also, there were two USB sockets, I could potentially use my new tablet to charge my phone if I left access available to the sockets. So this meant that if i did not want my usb power cable for the Pi board sticking out the side of the unit, it would need to be soldered on to the battery bank board. I did this by stripping down a USB cable, finding out which wire was which and soldering the two power cables directly to the battery-bank board, while leaving the other end with the micro-usb plug on it to plug in to the screen USB. The power runs from the screen, straight in to the PI by two cables, these are not soldered, just push-on, and they came with the screen kit.
Mounting the USB sockets for the battery bank on the side, means that I can still use the on-board battery to charge my phone.
I also needed to have a cutout switch on those cables because the screen will draw power, even after you shut down the pi, and the power bank will not shut down until there is no draw.
Also, once the battery bank is asleep, you need to press the button on the side to wake it up. My plan was to have a small button on the side that shorted out the button's terminals on the board, because the button on the board would not be accessible. However, not finding a push-button I liked (many were too big or too small), i used a pivoted twisted paperclip as a slide switch to click the original button. This also can be used to check the battery level as it turns on the battery status lights.
Status lights: The 4 bright blue LEDs were something I wanted to keep as a feature, so I sanded down the wood until it was so thin, you could see through it. I stopped it breaking through by putting some clear epoxy as a 'varnish' on the outside. Then once it was thin enough on the inside, i filled the sanded away part, with clear epoxy. I should not have mixed it so vigorously as i have lots of bubbles in it, but i realised this after I had mixed it and it is expensive stuff, so i used it anyway, bubbles and all. I should have also sanded it away in a perfect square too, when the light is off, it looks exactly like someone has sanded away the inside by hand and bodged it up with epoxy. :-) Still, the build is considered a draft case, i will do a better job on the next build.
Fortunately the battery was two pairs of batteries and i was able to just cut some sellotape and fold them in to a line of four. Then solder a couple of wires on to the connectors to extend the board across to the other side of the tablet.
I spent a whole evening trying to find the optimal layout of the pi board and the batteries, and settled on the layout you see in the pictures. Pi board in the corner to allow access to the usb ports from the side of the case. and the batteries on the other side. i need about 3mm more to make it not squeeze together so much, so I will be taking that in to account on the next case i make.
I could just make the wood around the sides another layer thicker, and then cut away a bit for the batteries, but i think with the quality of the workmanship, it could really do with a little more care taken on a new build.
On to treating the wood and I have a few plans to finish some other aspects of it and there are some other things I would like to do...
Step 4: The Finish
I am too impatient and have little time to work on these sorts of things, so i used 15 min clear epoxy for the glue, and the finish coat. I also got some thin cotton and laid it across the back of the wood and epoxied that too, as additional strength. The idea of using the balsa wood was because it was 2 euros from the DIY shop, and i could cut it with scissors and a knife. I had not planned for it to be the finished case, only a draft of what the final material would look like. It was also lightweight, so would not add too much weight.
The edge of the wood where it touches the edge of the screen needs either a better quality finish, or some capping. Here is the spooky part... I was looking for a way to trim the edge of the wood with the screen, like a little plastic capping for the wood or something. So I went on instructables and searched for 'tablet', thinking that putting an edge to a screen might have been solved already. Amazingly... i saw a picture of what looked exactly like my tablet!
So HowardT4 had already posted a very similar design using very similar components! How amazing that miles apart, someone was designing and building a Pi tablet too! I really like his use of an ipad mini battery, plus his use of plywood is much stronger than my balsa wood. I get the feeling that we have a similar love of ductape and big hammers.
Due to the sound issues with the Pi2 I am also waiting for a USB soundcard delivery this week. Plugging in a set of headphones directly to the Pi board is not a great experience. There are lots of audio issues when watching a movie, such as interference, popping and clicking (according to the Pi forums, common to the pi), so I am excited to see what the USB soundcard will be like.
The development of the operating systems for Pi are doing really well. There are a lot of very talented people working on these things and hopefully most of the slight annoyances will be fixed with the various systems.
As I have now spent so much time setting up Ubuntu MATE, I am tempted to try Raspbian again. I have a feeling that if I gave it as much time and effort as i have given to the Ubuntu setup, i might have a much better experience.