MTX Pi

Everything about Andy Key's great Emulator MEMU
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Dave
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Joined: 11 Aug 2012, 18:16
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Re: MTX Pi

Postby Dave » 10 Nov 2015, 03:02

Extensive modifications done to MTX keyboard to support separate functions for the reset keys for MTX Pi :-)
keyboard_mod_wire_640.jpg
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keyboard_mod_640.jpg
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Bill B
Posts: 103
Joined: 26 Jan 2014, 16:31

Re: MTX Pi

Postby Bill B » 10 Nov 2015, 15:07

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.

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Dave
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Re: MTX Pi

Postby Dave » 10 Nov 2015, 15:31

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

split_reset_640.png
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Kbd_mods_640.png
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Bill B
Posts: 103
Joined: 26 Jan 2014, 16:31

Re: MTX Pi

Postby Bill B » 10 Nov 2015, 20:29

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.

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Dave
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Re: MTX Pi

Postby Dave » 10 Nov 2015, 20:46

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

Bill B
Posts: 103
Joined: 26 Jan 2014, 16:31

Re: MTX Pi

Postby Bill B » 10 Nov 2015, 21:09

Dave,

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

Bill.


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