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Author Topic: mechanical Keyboard for the G7400  (Read 4714 times)
Blueleader
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« on: August 06, 2014, 05:09:03 PM »

I'm working on a new project.
A mechanical keyboard for the G7400 in order to be able to programm Visual Basic comfortably .

On the built G7400 keyboard some keys have two functions. Here I would like to use separate keys to minimize the use of the shift key. (eg the cursor keys)


So I have designed a Layout, inspired by the PC keyboards.


Unfortunately, the mechanical keyboard switches only have one pole. To enter a character from the second level, both pins of the character as well as the of the shift key must be pressed simultaneously.

eg: "%"
Here i have to connect 1 and 11 for the [$ / 4] and 7 and 17 operated for [Shift].


So I'm looking for a solution to switch 2x 2 contacts potential-free with one contact.

Relays are unfortunately too slow. I think with optocouplers that should be possible.
Unfortunately, I don't know much of it.
Has anyone of you experience with these parts and could give me hints?

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gertk
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« Reply #1 on: August 07, 2014, 07:51:48 AM »

You could use the old 4016 or 4066 CMOS analog switches, there are 4 on/off switches in each chip.

http://www.cmos4000.com/cmos/4066.html

Another approach could be to program a microcontroller with enough IO pins to convert PS2 or USB keyboard signals into the correct matrix signals for the G7400, you could again use the 4016/4066 to mimic keypresses to the G7400

In my C7420 emulator I can send signals from a host PC to the emulator over USB and let the host PC 'type in' a program or do it manually by using a terminal program http://videopac.nl/forum/index.php?topic=1616.msg14063#msg14063

Or you could turn it into this  Smiley (sorry about the blurry picture):
« Last Edit: August 07, 2014, 08:03:46 AM by gertk » Logged

>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
Blueleader
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« Reply #2 on: August 07, 2014, 09:30:23 AM »

Thank you for that info!
That seems to be a good solution.

I made a short drawing how i think to do it.
Am l right?

The only Thing I don't be sure is,how i connect the Control-Pins (+ or GND)

Your G7400 Keyboard-MOD looks great! Shocked
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Blueleader
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« Reply #3 on: August 07, 2014, 11:38:38 AM »

So, here the final shematics.
2 Questions open:

  • What polarity for input ?
  • Are the diodes necessary?

THX
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gertk
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« Reply #4 on: August 07, 2014, 09:32:53 PM »

Your G7400 Keyboard-MOD looks great! Shocked

Unfortunately it is only a mockup  Embarrassed

I never came to actually connecting it but I found that laptop keyboard and it fitted beautifully..
The LCD screen on that G7400 is very real though and some people on the forum have seen it in action already. Smiley

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>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
gertk
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« Reply #5 on: August 07, 2014, 09:41:28 PM »

So, here the final shematics.
2 Questions open:

  • What polarity for input ?
  • Are the diodes necessary?

THX

The polarity for the input signals is a logic '1' or 'high' for the switch to be 'on' and a '0' or 'low' for 'off'.

If you re-use the analog switches of the 4066 for other keys/functions you need to isolate the control inputs with the diodes. In that way you can switch 'on' a key by sending a logic '1' through a diode (kathode pointing to the control input). You need a pull-down resistor from the control input to ground to make sure it stays 'off' when not driven by any of the diodes. Anything between 10k and 100k will do.

Also make sure that the 4066 has its Vss (pin 7) connected to GND of the G7400 and it needs a +5 Volt supply on Vdd (pin 14) too of course.
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>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
Blueleader
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« Reply #6 on: August 07, 2014, 10:55:23 PM »

Thank you for the explanation!

OK, if i understand right, i have to connect +5V to control to set the switch to "ON", and GND to switch it "OFF"
What state happens, if switch to "ON", remove the +5V but didn't connect -5V.?

Will the Switch stay "ON"?

I made a shematic for one Key.
Did i understand all right?

Im unshure because the resistor is on GND and when i press the key, +5V and GND are connected through the resistor.  Roll Eyes

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gertk
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« Reply #7 on: August 08, 2014, 12:02:28 AM »

You can leave out the diodes. And you can calculate the current through the resistor by dividing the voltage (5V) with the value of the resistor (100k) and it will result in a small current. So no risk of shorting the powersupply  Smiley

You will need diodes if you want to use the analog switches of the 4066 for more than one physical keyswitch input. Suppose you need to activate the shift button for another keyswitch then you connect a diode from each of the keys to the control input of the analog switch for the shift function.

I can draw up a circuit diagram but I am on tablet now....  Smiley
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>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
Blueleader
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« Reply #8 on: August 08, 2014, 03:16:29 PM »

I tried to make a schematic again.
So that i've understood.

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Rene_G7400
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« Reply #9 on: August 10, 2014, 11:29:33 PM »

If you make a keyboard with 64 keys or less, another option would be to modify the keyboard translation table in the ROM of the C7420 coupling cartridge. (That's what I've done to be able to use the C7420 on my Odyssey3 console which does have a nice keyboard.)
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Blueleader
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« Reply #10 on: August 12, 2014, 08:45:10 PM »

I think this is beyond my ability by far.  Smiley
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TomBeck
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« Reply #11 on: August 12, 2014, 10:29:59 PM »

I think this is beyond my ability by far.  Smiley

I know this feeling, when René, gertk or Marc discuss something technical.  Cheesy

I am already happy, when my Jopac work, when I press the red powerbutton.  Roll Eyes

... but I am very happy that we have such people here in our forum.
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Wink  Killed the Killer Bees  Wink
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