Datanetics Rev B Keyboard

Datanetics Rev B keyboard

Image of Original Datanetics Rev B, courtesy John Calande - http://apple1computer.blogspot.com/

This is one of the most common keyboards that can be found with an Apple 1.   Here is a link to an original set of directions about how to connect this keyboard to an Apple 1.    When I get a chance I'll clarify and provide more understandable instructions  (check out my blog).

http://www.applefritter.com/node/2809?res=original




I have built a reproduction.   As part of the reproduction process, I reverse engineered the board and created a set of schematics.
datanetics rev b
            keyboard

Parts

Datanetics Inc. made their own patented keyswitches.  I've run across two types of these keyswitches, those with straight stems and those with slanted stems, as shown below.  The Datanetics rev B used switches with slanted stems.

Example Datantic
      Keyswitch
As far as I can tell, sources for original new keyswitches and caps are non-existant.  However, very early Apple II and Apple II plus computers used keyboards made by Datanetics. Most of the keycap set used by Apple is close enough to the Datanetics keyboards to be useful.  Early Apple II plus computers may be considered the only likely source for these Datanetics keyswitches and key caps.

The other difficulty is the keyboard encoder.  This part is a National Semiconductor MM5740/AAE.  This part is difficult, and sometimes impossible to find.  When you do find them, they frequently come with a mysterious defect that causes randomly repeating key strokes.  They are also sensitive to static electricity, so handle them with care, if you do find one.   If you can't find a working one, a micro-controller could be programmed to perform the same function.  It would have to be mounted on a daughter card, because the power connections on the MM5740 are in non-standard locations.  The data book and app. notes for this part can be downloaded  from here.

Stiffener Dimentions

Here is a not to scale rough drawing of the stiffeners used by the Datanetics keyboard.

stiffeners

Datanetics Rev b Reproduction

Datanetic's Rev B Reproduction
Here is my reproduction Datanetics rev B  connected to the Mimeo.

Build Your Own Datanetics Reproduction Keyboard

See my Datanetics blog entries for more information my reproduction.

A parts list can be derived from the schematic.
A couple of things to be aware of before taking on this project.
  1. The matrix vias are plated through and must be drilled out to eliminate connectivity between top and bottom copper layers
    1. this must be done carefully or you risk delaminating the copper pads
    2. the holes are drilled undersize, to .026 mils dimension, you should drill them out to about .036 mils (an  1/32" drill bit will do)
    3. use a sharp drill bit, in order to reduce risk of delaminating pad
    4. I recommend drilling partway through from each side, to reduce the possibility of delamininating pad
    5. check connectivity after drilling out with an ohm-meter to ensure that the connectivity is removed.
  2. This reproduction faithfully reproduces a mistake that existed on the original Datanetics rev B.  Fixing this requires cutting a trace in two places and jumpering.  My blog has details of this issue.
  3. The fit of the plastic studs on the keyswitches to the PCB holes may be tight.  If you can't get a keyswitch to mount flat to the keyboard, you can ream the mounting holes slightly.  There is no electrical connection in these holes, so removing plating is not important.
  4. There is no stiffener across the top of the board because unless it is insulated, it would short out the traces running across this area.
Corey Cohen wrote this build manual based on his experience building a reproduction Datanetics.  
Datanetics PCBs are all sold - As they were very slow sellers, I'm not sure when or if I will make another run.    If you can find around 10 friends that would all commit to buying  them,  I would do another batch.



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