Here's one of my latest completed projects:
“A” for Acorn, “7K” for 7000 and “P” for portable.
A custom built (by me!) portable Acorn A7000+ RISC OS computer system.
The main features are:
- Integrated 10.4 Colour TFT LCD using analogue RGB+HV video.
- Uses an original Acorn A7000+ motherboard
- Internal 9.6v 4600mAh NiMh Battery
- Custom power/voltage regulator to supply the internally required voltages
- 12v 2A external power supply input
- External mouse, keyboard, serial, printer and audio output ports
- Internal 4Gb compact flash storage
- Dimensions: 315mm x 205mm x 70mm
- Weight: 2.5Kg
So back in 2008 I had an idea of making my own very portable or luggable style Acorn RISC OS computer. After reading about a few other people doing the same. For example the Lego A7000 laptop or the A9home DIY laptop. It wasn't until around October of 2010 that I actually started designing what would be the A7KP. The design I went with was a tablet style system utilizing an external keyboard and mouse, similar to the prototype newsPAD. I did want a built-in touch screen but I scraped that idea in the end. Because finding a mini touch screen that would work natively with RISC OS would probably be difficult and expensive. I started the main build, both electronics and the case around mid November 2010. I had the system finished by the end of may 2011. I worked on this project on and off over this period of time. Though if I worked on the project constantly I would probably had it finished in about a month and a half.
Some more pictures of the system:
How I did it and how it works
The case is built up from a number of MDF side panels with four wooden corner supports. The front panel contains the LCD screen. It is sandwiched between two 6mm and 10mm thick MDF panels, with a 2mm thick clear perspex screen cover. So that the bare LCD screen is not exposed. The LCD screen sits flush inside the 10mm panel. The four screws located at the front of the system allow the screen cover (10mm MDF and 2mm perspex) to be removed. The back and sides are all 6mm MDF. The back panel is removable and is held on with four screws, so that the internals can be accessed. All of the side panels are glued on to the corner supports with strong gel super glue. It is all painted black with four coats of mat black spray paint. The internal components are held in with various brass and plastic PCB mounts. Overall the case is quite strong and turned out pretty well.
The Electronics and Components
The system can be run from either 12v DC from an AC adaptor or 9.6v from its built-in batteries. As system uses an original Acorn A7000+ main board, all the required voltages to run board must be provided: +5v, +12v and -12v with the use of some voltage regulators. I used three switching regulators from Texas Instruments to provide power to the system board. A PTR08100WVD is used to provide the +5v. The A7000+ board draws 480mA on its +5v rail. +5v is also supplied to the compact flash card. A PTN78000A is used to supply -12v rail. And a PTN04050C is used for +12v. (9.6v is stepped up to 12v while running on battery). The total current draw of the main board and compact flash card powered by the three switching regulators without the screen is 550mA at 12v. The total current draw of the complete system is 1.2A at 12v.
The screen used in the system is little 10.4 inch TFT PC monitor for use with point of sale equipment. (I brought it off ebay for £24 on an liquidation auction) It runs from 8v to 12v and only draws 600mA at 12v that made it a good choice for this system. I removed the controller board and LCD module from its case. De-soldered its VGA and DC input ports so that I could wire it directly to the A7000+ main board.
I made a few modifications to the A7000+ main board for this project. I replaced and re-soldered four larger capacitors so that they would lay flat to the PCB. I removed some of the connectors from the PCB so I could wire directly to them, the monitor/VGA port and DC power connector for example. I also removed the original CMOS battery and soldered in an AAA 1.2v 250mAh NI-CD battery as the original battery sticks out from the motherboard and has a tendency to leak.
For the hard drive a laptop 2.5 HDD would work but would draw more power leading to shorter battery life. So I used a compact flash slot to IDE adaptor and 4GB compact flash card to save power. I can remove the card and connect it to my Risc Pc to access, add and remove files.
On a full charge the system can last just under 3 hours. I added a feature where by the user can put the system in to a primitive form of standby mode. There is a button on the left side of the case that can turn the screen on and off, but keep the A7000+ powered up. The internal battery is charged by hooking up an external charger to a connector on the right side of the case.
Here's the 12v DC input. Originally the input jack was fitted into a hole next to the main power switch. But when I installed the power regulator board, the back of the DC input jack was in the way. And the case would not shut properly. So I had to remove it and add a simple connector block on the outside of the case. I then filled in the hole with hot glue and a black sticker. Doesn't that good but does the job.
Here are the I/O ports of the system. An external PS/2 keyboard and mouse must be used.
Some internal pictures of the system showing all of the components.
Replaced CMOS 1.2v 250mAh NiCd Cell:
How the A7000+ mainboard is mounted:
DC-DC convertor boards:
VGA port de-soldered and directly connected:
More pictures of the system:
Size comparison with the RISC OS 3 User Guide:
More pictures this project are on my photobucket:
There we have it! My home made portable RISC OS computer system!