Introduction: The Pi Tablet
Hello fellow makers, following on from last year when I made a Pi-Laptop, I will be making Pi Tablet (see the theme here!). Well I say its a Pi tablet but the main goal was to make a tablet which can house the vast majority of single board computers and each can be changed really easily such as the Raspberry pi etc. This project is not too hard to build and is quite cheap so I hope you enjoy this instructable.
PS: please vote for me in the competition :)
Second Prize in the
Microcontroller Contest 2017
Step 1: Parts and Tools...
Probably the most important step is the materials and tools needed for this build. Please remember these parts are just a guideline and don't be scared to experiment with other parts and ways of doing the project.
- Raspberry pi or the computer of your choice
- USB Hub
- Power button
- 7inch lcd capacitive touch screen
- 3.5mm female plug
- Battery 1s 5000mah lipo
- Bunch'o wires
- some spare usb plugs
- Adobe illustrator or a equivalent 2D Design tool
- Laser cutter/ cnc mill / good ol'fashioned saw :)
- screw drivers
- soldering iron
- hot glue
- electrical tape / heat shrink
- super glue
- hot glue
Step 2: Building the Case
For this build, just like my Laptop build, I used a laser cutter but this time I experimented with an online cutting service for the majority of the cuts. I have to give a shoutout to the guys over at Razorlab for the support they gave me. I normally design my cuts on a program called 2D design which is okay apart from the propriety file format and that the majority of industry actually use adobe illustrator. These guys helped me to convert my drawings and make sure they would work properly.
The main reason why I like to laser cut my parts is down to the ease, accuracy and precision that comes with laser cutting. Also not to forget that when using an online service like Razor lab, the price is very reasonable. However using a saw and cutting each part manually can work as well although the final finish if you are using clear perspex like me won't be as good.I have provided the drawings in both a dxf and a dtd and they are all in scale if you want to try it out yourself.
After the parts were cut, I did do a test fit of the case to make sure everything fit properly but I didn't glue the case until the other parts were made.
Case.dtd (for 2d Design)
Case.dxf (for everything else)
If you want me to add another file format e.g svg just ask
Step 3: The Power Supply
The easiest way to do this is to make use of those cheap usb backup power packs that you can get off amazon for under £20. However being the ambitious person I am I decided to make my own...
I wouldn't recommend this for people who are not experienced or skilled in the art of not blowing up a lipo and general soldering techniques.
For my tablet I decided not to use 18650 li-ion cells and use a 2s 5000 mah battery from hobby king. This is because the battery from hobby king fits perfectly in my case and is a whole lot lighter when compared to an equivalent setup of 18650 li-ion cells.
Most single board computers like the Raspberry pi require usb to power them or 5v at around 1-2A. The battery from hobby king was a 2s meaning it was 7.4v and only 5000 mah so to increase capacity and half the voltage I changed the cell arrangement to be wired in parallel. If you are going to try this make sure when modifying the battery that you don't short the battery or overheat it.
NB:Modifying lipos is like playing with bombs.
After the modifications are complete the new battery will now be a 10000mah battery running at roughly 3.7v. However the Raspberry pi won't take a varying 3.7v input so I used a cheapish charging circuit which does a few things. Firstly it allows for the battery to be charged with a micro usb plug and secondly it takes the varying voltage from the battery and uses an inline regulator to create a constant 5V supply.
Finally I soldered on an opposing battery connector onto the charging circuit while also soldering on the negative lead of a micro usb cable to the negative output on the charging circuit. The positive output will need to be soldered onto the common pin on switch and the positive lead of the usb cable will need to be soldered onto the other side of the switch. Remember to allow enough slack in the wires so the components can be fitted easily in the case.
Step 4: IO
To allow access to the usb ports when the tablet is assembled, I used a usb hub which allowed me to have 3 external usb ports and 1 internal port. First disassemble the usb hub and discard of the case. Next I add some hot glue to where the wires are soldered to firstly provide some strain relief during assembly but also to insulate them. Finally glue on the plastic cover to the front of usb hub with super glue so it can be easily slotted into the case.
3mm Headphone port
This part is really easy. Take a 3mm headphone cable, strip one end to reveal either two cables, or a single cable with shielding. If your cable has two smaller cables inside then find which cable is positive(normally red) and negative(normally black or blue ) and solder to the corresponding pins on the female plug. If your wire has 1 wire in the middle with shielding, the shielding is negative and the middle wire is positive. So solder the shielding to the negative pin of the female jack and solder the centre wire to the positive plug. I have attached some diagrams to show the polarity of the plug. Again I test fitted and tested the audio before installing it.
Step 5: HDMI Soldering
This is probably the most difficult soldering part of the whole project. I would recommend trying to find a flexible thin HDMI cable but I found that the majority of HDMI cables have a bulky plastic shielding in their plugs which are not very useful for a tablet. I definitely spent at least an hour on it if not more. I have attached a diagram which should show you the basics and here's a link to a video which I made a while back for my laptop, it gives the general idea but just ignore the part about threading wires through a hole.
First off you want to tin your HDMI plugs. The HDMI plugs already have solder pads but tinning them is recommended as it makes soldering the wires much easier. Next you want to get thin wires. I would recommend IDE cable as it can be easily bent and is thin so fits well in the case plus you can recycle the wires in that old beast of a computer from the 1900's which still uses IDE drives (heheheh...) . Cut two strips of the IDE cable, one with 10 wires, and another with 9. Cut the cable down to length so it fits well in the case and strip of the insulation at both ends to reveal the bare copper wire inside. Solder one end of the IDE cable to the first HDMI plug, twist the cable upside down, and solder the other end. Repeat this for the other side for the HDMI plug and test it out. If you get no signal first check the connection and then that you have the wires in the correct orientation.
Step 6: The Screen
First thing to sort out is the power for the screen. The screen requires a micro usb cable which not only powers the screen but also drives the touch part of the screen. Therefore the screen needs to be powered off the raspi usb port. A thin micro usb cable is needed but as I didn't have one available, I made one from a bare micro usb port, a bare usb port and some wire but you could strip off the insulation carefully of an existing cable.
The case I made was specifically designed for my screen so I included the mounting points which meant the screen was held well. I installed the screen in the top part of the case to make it easier when the whole tablet was assembled. I made sure that the bottom piece of the case could be removed easily so that I could replace the screen if need be.
Step 7: Case and Assembly
The top half of the case is where the screen sits and is also where the machine screws will be fitted to fasten the whole case together. For the bottom half, I started from the bottom up. First the parts are test fitted on a jig using the 4 machine bolts to make sure the parts fit well. Next stage by stage, each layer is glued using a few drops of super glue and every layer is checked so that the case is square.I didn't glue the middle layers so that I can easily open up the case if I want to change out the board or change the battery etc.
To mount the pi, first bolt on mounting screws to the pi, apply a bit of super glue to the heads of the screws and place the pi in the recess in the case, and glue the screws in. This means it is easy to mount and unmount the pi in the case and this method will work with any single board computer as long as it fits in the recess.
Next all the ports are fitted to the case. The usb port simply slots into the topside of the case and is stuck in with a few drops of super glue. The charging port, which is the micro usb port, is glued into the little slot on the side, and finally the audio port is screwed and glued into its corresponding slot.
Step 8: System Setup and First Startup
I used a fresh install of Raspian for this tablet and I find it works really well. Before starting up the tablet, make sure the battery is charged fully and all the connectors are properly inserted. Insert your SD card and push the power button and it should start up right into the desktop.
- The touch screen works great on its own for mouse movements but for keyboard I recommend either using the mini wireless keyboard or installing a software keyboard using
sudo apt-get install matchbox-keyboardclick here for more info.
- Here is a link to a guide to set up Raspbian.
- If you enjoyed this instructable please vote for me in the competition as I would greatly appreciate it:)
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