Much has already been written about using the Motorola Atrix Lapdock (essentially a portable HDMI monitor with a built in powered USB keyboard, trackpad and hub) coupled together with a Raspberry Pi. The Pi being powered by a micro USB makes it a suitable candidate for using it as a low powered portable computer.
You can still pick up a Motorola Atrix Lapdock for a lot less than it’s original £300 or so selling price, although I’ve noticed that prices have started to creep up – expect to pay between £60-£80 for one. There is a newer Motorola Razr Lapdock available which I believe uses the same ports, so hopefully these very useful devices will continue to be produced and supported in the future.
This week my ModMyPi case finally arrived – it’s an injection moulded click together case which is beautifully made -
I have already hacked together a cable to connect the lapdock and pi together – but I wanted to make a more portable and neater version. Plus using an HDMI micro adapter would provide a mount to hold the Pi in place, in the same way that a phone would be docked:
The lapdock provides a USB micro male, and HDMI micro male connector (note – micro not mini!). The USB provides power and data over 4 wires, and the HDMI video and sound. To marry this to your Pi you’ll need to take the power connection to a male micro USB plug, and data to a male USB plug. Most people who’ve done this modification have also broken the power connection to the data plug as a precaution. In my version, I’ve included a power switch to make it easy to turn the Pi on and off – opening the lid of the Lapdock also cycles the power. Obviously this is all entirely at your own risk.
Here’s my wiring diagram:
To do this you’ll need in addition to the Lapdock:
Edit: I’ve noticed that some of the items are listed as being out of stock – the crucial thing to search for is HDMI micro female and micro USB female to get the connectors you need for the lapdock.
- A micro HDMI female to HDMI male adapter / MicroHDMI = HDMI “D type” (also available on ebay)
- Optional: this HDMI adapter pack came in useful as well
- A micro USB female to male adapter (these are surprisingly difficult to find – ebay is often your friend here)
- A regular USB female to Male cable (or you could use a micro USB male to USB male cable – I wanted the flexibility to use different lengths of cable)
- A switch (Maplin or ebay) two or three pin on / off – just not momentary.
- Something to use as a wiring box – the HDMI adapter holds the Pi in place quite nicely, so you could just wrap a bit of insulation tape round everything. I made a box out of a plastic screwdriver holder that came from poundland)
- A wire stripper – these ‘automatic’ wire-strippers work well
- Soldering iron and solder (soldering isn’t too hard, but a lot of people are put off by the idea of it – a bulkier but soldering iron free alternative would be to use terminal blocks)
- Craft knife
- Epoxy glue or (better) some Sugru to hold everything together
First off you need to get the two micro adapters to fit together – check with the lapdock and carefully trim away the surrounding plastic until they both fit together. Then glue the two adapters together, whilst they’re plugged into the lapdock. Be very careful not to glue them to the lapdock itself. Then expose the wires from the micro USB adapter – you might have to trim into the plug itself to do this. USB cables consist of red, black, white and green cables sometimes with a metal sleeve around them – you can cut the sleeve away and discard it. Be careful not to go through any of the wires themselves.
Here’s the underside of the adapter – showing the two trimmed plugs side by side, glued together with epoxy Edit: I’ve now used Sugru to hold this together – the wires from the USB adapter on the left feed into the box where all the connections are made:
Then cut your usb cable in half and expose the individual wires. Strip the ends of all your wires together. Then solder them together as per the diagram above. The power USB cable needs red and black connected – the data USB cable needs white, green and black connected. Put the switch on the red wire between the lapdock and USB power cable.
Once everything is soldered together, you can give it a quick test by plugging in the Pi to the lapdock. If everything goes ok, once the lid is open and you can boot and test the keyboard. If it doesn’t work, check the connections and that the HDMI adapter is fully plugged in.
The final result is the Pi sitting on the lapdock behind the screen.
For extra neatness you could always mount the switch on the case itself and route all the cables internally, but there you go – a practical portable Pi Laptop you could just chuck in a bag and take with you, and that doesn’t alter the lapdock in any way.
Update: a few tweaks
After a few weeks of use I had a few connection issues with the wires inside the adapter and the quality of the epoxy – so I resealed the unit with some Sugru self-setting moldable rubber and resoldered the connections – the Sugru also helps to avoid the potential of short circuits.
I’ve also swapped the modmypi case for the more colourful Pibow case – this is a little bit larger than the modmypi case so I needed to use a right angle HDMI adapter to get it to fit. The Pi now sits at an angle between the lapdock and the desk – thus:
And finally I’ve added a Edimax EW-7711UAN USB wifi adapter (with lovely antenna) which now works out of the box with the latest (September 2012) version of Raspbian.