D2 Keypad construction
One of the major stumbling blocks trying to emulate older micro boards is the shear size of them (compared to current size micro controller boards). This makes any retro design rather expensive (mainly due to pcb costs). So attempt has to be made to minimize costs to make the venture plausible.
Many early micro boards had keypads for control and data entry (including the D2 Kit). So here is an attempt to mimic the keyboard matrix of the D2 kit, and use it later on as part of the whole micro system. This can be equally applied to any of the other micro boards.
Before I go on..some people will argue why even bother with the keypad ..when you can reconstruct the basic functioning say through a serial port and minimize all the cost. True… but does not replicate the functioning of these early systems. You may as well use one of the latest micro controllers/microprocessors or FPGA's and emulate the lot.
With D2 lets look at the keyboard circuit part of the design.Here is a snapshot of the schematic…
D2 had 2 major boards MPU/memory and interface/display and keyboard board of which the circuit is above. So as far as the keypad is concerned it is basically a matrix (6×4) and all the connection go back to buffered PB0 to PB7 port and X0-X3 output of MC14539 IC.
Hence as a design we can just have the keypad matrix by itself and provide a ribbon type connection of at least 10 lines to the 6821 and MC14539 IC. Everything else (including the 6 digit 7 segment display can be put on the main board). That way any key type buttons can be mounted on a matrix type breadboard and minimize construction costs.
I did similar design for the SYM-1 mini board but the issue with those pcb type buttons is that they had too much play in horizontal direction hence the alignment of them was not that good. Since then I found these matrix keypads on Ebay that have clear plastic caps so was ideal for D2 Kit type keyboard.You can also buy individual keys …but you be better of buying the matrix as it is already mounted on a metal type frame..which should be easy enough to mount to a box.
This gives you 25 keys (1 extra that can be used for say RESET function key) which can be layed out much the same as original design.(see pic at the top of the page)
Each key top has slight indentation (about 9.5mm x 9.5mm) where you can insert bit of paper to make each key name.
This is just to show you how some keys would look like (see pic above)…
You can use any graphic design type software to generate the image top of each of the keys to 9.5×9.5mm dimension.( I used Adobe Illustrator.)
But in case you cannot be bothered here is a pdf of the keys . .which you should be able to print … and where key images should be to correct size.
Download key images (pdf).
Wiring up keypad
If it is standalone keypad just wire up back of keypad matrix to an IDC female connector (16 pin) that will later on plug into main CPU board.
Note that “E.” is the Blue EXAMINE key ..different to the HEX “E” key. RST is the additional 25th key which is connected to 0V(or ground) and the Reset line of the micro board.
Layout of keypad and pcb design?
You can layout the keys as per schematic above, which would make the wiring relatively easy. That is have all the function keys (blue) in top two rows and all the hex numeric keys in the bottom 4.
If however you are keen and want to lay them out in a similar way to the original D2 keypad (top pic), the the following pcb design might help.
Please note I have not constructed any of the pcb design below, so use the following with caution.Please check all dimensions and layout before making anything. I am providing all the source Diptrace files so you can alter them if need be or use it as a starting point for any similar keypad type design.
Here is pcb layout with top and bottom traces below, which can help you in wiring the keys and the IDC connector. this design would be if you are using individual keys and mounting them on the pcb. My suggestion is to consider the matrix type keypad setup first ..and then try something like this if the premounted versions will not suite.
From the above diptrace file you should be able to generate any Gerber files for pcb manufacture.
Well there you are ..once you construct the keypad ..you need to do the rest .. :) which would be on the main board. In case you do make some of these pcbs ..let me know ..Happy D2ing!!!