*** M E M O R U M ***

Extensive modifications done to MTX keyboard to support separate functions for the reset keys for MTX Pi

Dave,

I made three suggestions for modifying the keyboard:

1. Connect the mid point between the reset switches to one of the keyboard drive lines.
2. Add a 21st connection to the mid point between the reset switches.
3. Connect back to back diodes across the reset switches.

If I understand your photos, you have opted for option 2. Is that correct?

I will probably try and support both options 1 & 2 in the software. Probably not option 3 unless there is much demand.

Bill.

Hi Bill,

I wanted to minimise any messing with the original keyboard, so have only made a single connection as shown in the photo, although wired to one of the switch terminals, it is logically in in the middle of the two switches - Option 1. The new connection is wired to DR7, but not on the keyboard PCB, it's done on my breakout board so that I can remove the connection by just removing a link.

regards
Dave

Dave,

OK.

The point of option 1 is that it could be done with a point to point wire on the back of the keyboard PCB, and does not require a flying lead. Probably neater, although it does require two solder connections to the PCB.

Having bought the mid-point off board (option 2), then the obvious thing to do would be to connect the mid-point to 0v, and the two end points to GPIO pins. This saves having to output anything to the drive lines before testing for a reset key press.

But as you say, what you are proposing is electrically equivalent to option 1, and will also work.

Bill.

Hi Bill,

it would not have been a problem, but I wanted the ability to disconnect the mod without having to do it at the back if the keyboard - hence the off board jumpers. I can make the DR7 off board connection to ground if you like? It sounds like it will make the software slightly simpler.

regards
Dave

Dave,

Up to you. It is worthwhile supporting both options in the software anyway.

Bill.

anyone tried PI Zero, as I understand its a very cheap PI ? but should be powerful enough.

Claus,

I agree that the RPi Zero should be powerful enough to run MEMU, particularly with offloading the video scaling to the GPU.

I haven't actually tried MEMU on an RPi Zero (although I do have one). I have used it on an old RPi B+, which I think has the same processor, and that works fine.

Bill.