4x4 matrix keypad replacement/emulation

[rawelk]

The situation: Two 4x4 membrane switch keypads are used in a proprietary control system. The OEM doesn't want to support the system anymore, and will no longer supply the keypads. These keypads plug into a proprietary circuit board which contains keyboard decode circuitry, and I2C addressing and communications to send keyboard entries via an I2C comm link to the control processor. I'm not considering fooling around on the I2C side, but figure 16 contact closures aren't too big a deal.

Haven't looked at one in awhile, but think I can visualize eight stabs on the rear of this keypad, so figuring it must be a matrix output type. Complicating factor: one keypad is simply zero through nine, and the remaining keys have fairly extensive text to explain switch function (small text - maybe 4 or 5 point, in up to 3 lines x 5 characters per pushbutton). Buttons on the other keypad are chock-a-block full of text.

I'm thinking there are four options -
1. Find out who made the keypads for the OEM, and see if they'll continue to make them, and sell directly to us. This would be best, but I'm not holding out a lot of hope.
2. Have a shop that does custom work (Pannam, Nelson, Ecco, Grayhill, others) replicate them. I've never gone this route before, but would imagine there are minimum order quantities, set-up fees, and other complications down this road.
3. Get and use an off-the-shelf unit such as a Grayhill 86BB2-006, and create, print out, laminate, and post a cross-reference for standard key nomenclature to our text. Probably the cheapest option; don't know how it'll fly from a user perspective.
4. Buy an inexpensive small mono touchscreen/PLC combo (something along the lines of an EZTouch PLC) fitted with discrete relay output modules (i.e. - 2 terminals per relay, N.O.), create a screen display emulating the keypad, connect the relays in standard switch matrix X1-X4,Y1-Y4 fashion to a suitable connector, and plug this into the existing keyboard decode/comm interface board.

Debounce and decode are all part of the proprietary board that does the I2C communications interface, and I'm figuring a relay output doesn't have any more bounce (could be wrong here) than pressing on a dome membrane keyswitch, so this ought to work. Problem with this approach is it may be the most expensive.

Two questions:
Does anybody have a feel for per unit costs in small quantities (under 24) if going the custom keyboard route?
Has anybody done a "touchscreen 4x4 keypad emulator" as outlined in #4, and, if so, were there any "gotchas"?

 

[itsmoked]

Are you going to re-market these things or is this just to support a fixed number of machines?

I have used the Grayhill keyboards many times. They are quite robust. They have a version that the key tops come off so you can put labels under them.

I had a large Italain leather spraying machine that had a crapwad membrane switch that had contacts that were failing(1.2 years old). Very hard to get replacements. I used a Grayhill and hacked and glued the membrane to connect up the Grayhill. It looked like hell but worked for many years.

RE your questions.
These guys work on an "earning per transaction" just like the PC board people. They have a price that they won't bother doing business below. So you can get 1 PC board for $600 dollars or (2) for $300 each or (3) for $200 each... You get the picture? So they don't really care about the quantity as the difference between physically building 1 and three boards is nil they just won't 'hunt' for less than $600.

Same with these keyboards. I would guess for the simplest possible layout color scheme you are talking about 8-$900 minimum. They'll cough up (25) for that or one for that. For image reasons they may charge another few bucks for (25) so they don't have to explain their logic.

#4 may cost quite a bit. So much that you shouldn't go that route unless you can also greatly increase the functionality. If you were going to that much hassle then it might make sense to upgrade the entire control system.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rawelk]

Thanks, itsmoked, for the ballpark on custom keypads. I priced an EZTouchPLC (6" mono touchscreen), and 16 bits of relay output) that would do the job for about $670, so it vs. custom keypad isn't too out-of-this-world.

They are for in-house use on eight systems (16 keypads), and I'd actually prefer to start over, and build new control systems from scratch. All the analog and digital I/O, DC drives, computer control boards are proprietary as well, and I fear keypad replacement will only be the first (and easiest) band-aid ... but we haven't consigned ourselves to the inevitable yet

That said, I'll take a closer look at the Grayhill line to find the one you mentioned with user customizable legend capability, and probably end up using them.

 

[VEBill]

Although normal telephone keypads are obviously 4x3, the full DTMF ('touch tone') keypads, including the A, B, C, and D keys, are 4x4. They're obviously relatively rare, but if you can find a source they'd be rugged. And the ones I've seen are made from individual switches so that they could be wired up any way you want.

 

[itsmoked]

Hi rawelk.

Thanks, itsmoked, for the ballpark on custom keypads. I priced an EZTouchPLC (6" mono touchscreen), and 16 bits of relay output) that would do the job for about $670, so it vs. custom keypad isn't too out-of-this-world.

$1000/25 = $40
Which is $640/$40 = 16x more.

$16,000. That's ballpark for a redesign.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rawelk]

Need to read more clearly in the future (or maybe its just some ballparks are bigger than others
I read $900, but not the gist of what you were saying about quantity.

It doesn't matter much, 'cause I'm not going the HMI route.

I was in the plant today, looked deeper, and find my assumption off by one pin, and four buttons ... its a 5x4 matrix, not a 4x4 matrix keypad, and is a Grayhill 88 series.

A blank keyboard, and clear overlay will set me back about $46. Will need to make my own legends, but I can live with that.

 

[itsmoked]

Das'ist cool.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com