Using The BBC Master Compact Portable

Well RetroChallenge is over but I got chance to finally complete one of the suggestions on Twitter...

Well I put on my summer clothing and headed out to Llandudno.
Here I am playing REVS on the Beach in the blazing UK summer sun (of which there was very little).

Had to fight my way onto the beach through the hordes of Spectrum and Commodore 64 users...

More Wiring Up

Completed the various wiring bits that needed doing. Made a power board that connects the incoming power connections to the main circuits via a removable umbilical that can be removed to disassemble the machine.

Cut the circuit boards down to size with the Dremel and tied the cabling together with tape.

Glued the main power board into place.

Added in the secondary power board that provides the switching between internal power and external mains.

Connecting wires between the power boards.

VGA Output

Connected the VGA wiring harness to the internal resistors, found the ones I needed from the maintenance manual that has a full circuit diagram of the machine.

Testing the output. Works ok but there seems to be a weird problem with colours not working, the output is correct but everything on the screen seems to be white.

Power Switch

Fitted the power switch that allows me to turn on battery power.

Finished Machine

The machine pretty much completed.

Switched to battery powered mode. Screen is showing MOS command prompt.

Look no wires :)

Outstanding Bits

There are a few issues that I still need to resolve.

Firstly the VGA seems to not be displaying colour, not sure if it was just me or if there is an issue. Need to check the actual output on a real monitor to ensure that we are getting colours.

Battery needs to be fixed internally in some kind of holder so that it doesn't get hot from any chips on the board.

The original brown front has been removed, I want to get a new custom vinyl printed that will also cover the screen boarder. Didn't manage to get time to design and get it printed.

GoSDC is working ok but I'm not sure what I'm doing wrong as the patched ADFS and DFS won't seem to load.
Not getting any errors from it but the filing systems I've asked it to load don't appear. Going to try it in the normal master and see if its an issue with the Compact.

All Good Thing Must Come To An End

Well that's me done for this RetroChallenge. Looking forward to reading everyone else's blogs. See you all in the 01/Winter :)

Fixing In Place

Started by cutting down the main power board using the dremel and hot gluing it in place.

Wiring It Up

Wired up the harness to connect the VGA convertor board to the TTL RGB output of the BBC. The hooks will be connected to the resistors on the inside of the board. This means that I don't have to solder the entire lot to the board.

Just need to trim down the board using the Dremel.

Sorted out the power switch which will allow me to switch between the external power and battery.

Next job is to wire up the internal power to all of the above items.

Cutting Tracks

Had to do the bit I was not looking forward to. Cutting through the power tracks on both sides of the board.

Was a bit worried about damaging the board but was careful to remove the track with a Stanley knife without damaging anything else.

Gluing Bits In Place

Glued the power connections in place to stop then moving and protect the board.

Added in fixings for VGA convertor board.

VGA convertor board now fixed on mountings.

Soldering Power To The Main Board

After about an hour of fiddling around managed to solder the 4 wires which will take the power from the external socket to my board and back. The solder on the machine is lead and it does not want to melt. I had an absolute nightmare getting the wires through the board and getting the solder to melt on both sides. Finally after lots of fiddling got the wires soldered on.

Next tested that it actually will work from the battery. Machine initially kept powering off after a few seconds. I found the reason, i'd managed to short two of the connections on the back my perf board. Sorted that out and it works ok.

Next thing to do is cut the tracks so that the input wires are separated from the output ones, the input will power the charger and the VGA convertor board. The power from the battery board will then go back into the machine (or be powered via the input if the switch is in the correct position).

VGA Convertor

Due to the VGA converter drawing lots of power I have decided to make it available when the machine is powered via mains. It adds too much drain to the battery and is not really useful unless you are at a desk anyway.

Originally I was going to have everything powered by the battery and the unit could be powered off via a switch but would always be charging if plugged in.

The machine will now do the following...

1) Always charge when plugged in.
2) The VGA convertor will be powered when plugged in only (from the incoming 5v).
3) The machine can be powered externally while the batteries are charged or you can use the battery to power the machine and the small screen. Thus the small screen is only available when on battery power and turned on. Where the machine is available if using battery or on external power (as the original machine was) dependant on the switch position.

Battery Testing

Tested the battery (2000mah) and found that with the small screen and the machine powered it will provided about 45mins to an hour. Have managed to get the battery I was originally going to order (but was out of stock) which is 6000mah so gives several hours of usage.

Screen

Mounted the screen in the case.

Firstly marked out where the screen should go and used the dremel to cut out the hole. I left a small set of lugs from the lower plastic area so that the screen can sit on them. It turns out the screen was exactly the same height as the indent in the air slots so it fits nicely.

Inserted screen and adjusted to fit correctly.

Hot glued the screen and the board into place.

Tested to check everything works ok.

Installed SD Card

Dismantled the Compact and installed the GoSDC into the ROM slot.

TV Display

Tried to power the small TV display from the machine but found it requires 6v. Going to have to add another Step-Up to the power board to provide the 6v it requires.

Update: Wired in the extra Step-Up, Adjusted the voltages on the Step-Up boards so that one is 5v and the other 6v.

Connected the power board to the BBC externally and checked that everything works ok. Board is powering the screen, Gonbez board and the BBC from the battery.

Then tested the TV board, connected to the external video out and got the following.

You can just about make out the Acorn MOS and the command prompt. This looks better in real life the camera doesn't do it justice. Next step is to get it to run something on the screen.

Battery & Charging Circuit

Well some parts I'd ordered arrived so I decided to solder them together to test out the chargeable battery.

Here is the current charging circuit connected to the mains and the Gonbez. I can remove the power from the main socket and the battery takes over.

This should hopefully provide a 5v input which will charge the LiPo battery when the unit is plugged in. I intend to wire a switch in between the charging board and the step-up board so that I can turn off the machine without stopping it charging.

The charge circuit takes 5v in but the battery is 3.7v. To be able to supply the 5v needed for all the internal boards I am using a step-up board that will take the 3.7v to 5v. I have tried it with the Gonbez board and it runs this ok.

Mini TV Screen

I have a very small TV screen which I bought. The next step is to wire up the screen check it works with the output from the BBC.

The Problem...

I currently have a BBC Master setup on the desk in my office. The problem is that its not very portable, if I want to take it anywhere it requires a large CRT monitor or my recently acquired Gonbes VGA convertor board, a modern monitor and a set of power supplies.

You then also need to take either a disc drive or the DataCentre to give me access to disc images so that I can actually do anything.

Solution...

I have a spare BBC Master Compact which I intend to make much more portable.

To do this I intend to add the following to the machine...

1) As the original BBC Master Compact uses a large desk unit to house the disk drives I need an internal method of storing software to run on the machine.

So I bought a GoSDC board which adds an SD card allowing me to store all of the software I need to use. The device plugs into a spare ROM socket internally in the machine.

John Kortink who designed the board was kind enough to supply one without the headers as he thinks the Compact may not have enough room inside with them attached. If this is the case I will need to wire a set of switched to the board to enable and disable it for updating the firmware.

2) So that I can run the machine away from any kind of power supply I want to add an internal rechargable battery.
Probably a lithium one with a charging circuit to provide a few hours of usage without needing a power supply. Obviously when the power is supplied it should cut off and charge the battery instead.

As part of this I will add in a power switch so that the machine can be easily turned off and will allow for charging without the machine being powered up.

3) To provide a VGA output I will fit the Gonbes board internally and provide a VGA socket on the back for connecting an external monitor.

This will require the power to the board and the TTL RGB output from the BBC to be wired to the board,

4) So that I can use the machine while on battery and without a VGA monitor or TTL RGB one I intend to provide a small screen built into the machine. This will probably be a 3-5 inch screen added to the top area of the case. Depending on the screen type this will either be wired to the composite out or to the second port on the Gonbes board.

This should be a mirror of what is output to the VGA / TTL RGB. I might put a switch in to be able to turn it off as it will display even when connected to an external monitor. If I have time it would be cool if when the external monitor is connected it displayed a cool logo.