If you have been following this thread, you will be aware that I have been designing a level shifter board that allows a Raspberry PI Zero, 3B or 4 to be interfaced with the BBC / Master 1MHz port. This allows various pieces of hardware to be emulated on the Raspberry PI. Currently, the following hardware is emulated:
- ADFS Harddisc (BeebSCSI implementation)
- Music 5000 / 3000 (with audio playback through the beeb / master internal speaker)
- Expansion RAM
If interested in purchasing one of these boards, then please either reply to this thread, or drop me a PM with your specific requirements, and I'll be back in touch.
The standard 'under keyboard' level shifter board
The level shifter board is designed to be plugged directly into the 1MHz port on the underside of the beeb / master. A Raspberry PI Zero, or ZeroW can then be plugged into the level shifter 40 pin header, and everything will sit nicely within the well under the keyboard.
Remote Installation Options
There are a couple of different ways to connect the standard 'under keyboard' level shifters remotely to an external RPi. Both options are equally good, but my recommendation would be to go for the Female / Female cable + small adaptor board; particularly if you're going to mount it in a case as the pins come to the edge of the case and allow the cable to be unplugged quite easily. It's also a slightly cheaper option, however, it does add some 'bulk' to the whole arrangement, and if you're not using a case, the Female / Male solution may look more elegant. It really is end user preference!
DO NOT TRY TO MAKE A FEMALE / MALE CABLE BY JUST PLUGGING HEADER PINS INTO THE SOCKET OTHERWISE BADNESS WILL OCCUR. THE UPPER AND LOWER PINS GET SWAPPED IF YOU TRY TO DO THIS, AND YOU COULD DAMAGE YOUR LEVEL SHIFTER OR THE BEEB.
Using a Female / Male cable
The first photo shows the male connector plugged into the level shifter, and the cable coming out the 'rear' of the case. The second photo shows the ribbon cable coming out the front and under the case. The photos also show the 1MHz unit with a power cable plugged into the 'rear', which is used to power the 1MHz RPi and level shifter.
Using a standard Female / Female cable + small adaptor board
With this option the cable comes out the 'rear' of the case. The 1MHz unit also has a power cable plugged into the 'rear', which is used to power the 1MHz RPi and level shifter.
Powering the level shifter and Raspberry PI
Please note that it is necessary to provide power to the level shifter board, as power is not available from the 1MHz bus. Various power options are available.
- If mounting remotely, then you should power the Raspberry PI directly from a standard micro USB (or USB C for the RPi 4) power supply. The level shifter board will then draw power from the Raspberry PI power supply.
- If plugging the board directly into the 1MHz port on the underside of the computer, then the preferred method is to pick up power from either the user port, or the tube port. A short cable will be supplied for this purpose. If both of these ports are in use, then an alternative 5v power source will need to be found. If using PiTubeDirect in the tube port, then I have designed a level shifter board for this port that has a pass through power connector, which will allow you to pick up power from the tube port, whilst still being able to use the port for PiTubeDirect. Details of this board are available in the next post below. The RPi Zero(W) will then be powered from this power source.
- Cost for standard 'under keyboard' level shifter is £15. This includes UK P&P. Please add £1.50 for postage to Europe and £2.50 for postage elsewhere.
- For remote mount, I can supply a standard female / female ribbon cable (approximately 80cm) and small adaptor board, all for £7.
- Alternatively, I can supply a female / male ribbon cable (approximately 80cm) for £8. Note however, that I have very limited stock of the male connector.
Acknowledgments - Please send me a PM if anyone else needs to be added to this list for their contributions
dp11 - for the original 1MHz bus level shifter concept, for the software & for helping to test
hoglet - for PiTubeDirect, and for helping to test
BigEd - for PiTubeDirect
simoni - for the original BeebSCSI code