[Photos] 1978 Harris Smart Terminal with Digitran capacitive leaf switches

I posted this project originally on geekhack but I thought it would be good to post it here as well since it's a pretty uncommon board and I haven't seen this specific switch on the wiki.

This is an old Harris board from the first year after they bought out Sanders. Earlier boards of this series used Keytronic foam and foil as seen here photos-f62/key-tronic-pcb065-01614-002b-t3594.html which is exactly one year older than mine. Electronic guts wise it's basically just a rebrand. However they did change the keyboard module, or at least offered more than one option. Caps are interchangeable between both types.

Image




The keyboard was made by Digitran and has very nice double shot spherical ABS caps. It has type of linear switch that consists of a spring and plunger that presses down on a z-shaped capacitive leaf soldered to the PCB. Actuation force is about 50g. The patent for the mechanism is dated 1974, but this board I have is the oldest example I've been able to find. The switch continued to be made up into the 80's at least and I've seen some industrial keypad stuff from them that might even be a little more recent. Here's an advertisement for them from 1982.

Image


So to the keyboard itself. I bought the terminal board off a reseller on ebay who got it from a hospital it looks like. The board had an "outpatient" sticker on it when I received it. Other than a massive carpet of dustbunnies under the keys, it was quite clean overall but the ABS was pretty yellowed.

Image




Cleaning begins. Here's a good shot of the copper leafs, controller and the rest of the PCB. Notice it uses a 8x16 rowxcolumn design so an xwhatsit Model F controller is perfect to bring it into the modern era.
Image
Image



This is the plunger plate that sits on top of it. Angled heads to the stems to create the stepped profile, and pretty simple all around. Not that fun to pull keycaps off of without some practice though. The way things were gunked around the springs before it was cleaned, it did appear to be lubed originally. I found I definitely needed to lube it with some dielectric Superlube to get the keys to feel right.

Image
Image


Desoldered all the old controller stuff as it was the only feasible way to hook up a new one. It took way longer to make notes of all the parts, their tested values, where they went, and storing them in antistatic bags than actually desoldering itself.

Once ready, the xwhatsit hooked right up. Rows to rows and columns to columns. Voltage was set manually. 152 milivolts has the keys actuate right at about 2mm of travel but you can adjust it anywhere between that and bottoming the switches out at 250. xwhatsits utility made it really easy to map the keys the way I like for a usable modern layout with several extra layer options.

Image



I was working on the case and keys at the same time, trying some retrobright that worked nicely but cleanup would require a lot of hand polishing away minor blemishes and bleaching of the colored parts of the keys.

Image

Image



And after repolishing the whole set of keycaps to return their natural color.

Image


All in all, a great keyboard. Still using it every day.
Last edited by Sangdrax on 05 Jul 2017, 19:20, edited 1 time in total.
Sangdrax

Unread post05 Jul 2017, 18:30

X
Sangdrax
 
Posts: 9
Joined: 05 Jul 2017, 06:50
Location: Acadiana
Main keyboard: Harris 1978 Terminal
Main mouse: Mammoth
Club member: -
 
I do remember seeing HaaTa's board but I don't think I've ever seen Digitran capacitive leaf switches before. Could you please show us some close-ups of the swtich thanks. Great keyboard BTW, thanks for sharing!
seebart
User avatar
Offtopicthority Instigator

Unread post05 Jul 2017, 18:40

User avatar
X
seebart
Offtopicthority Instigator
 
Posts: 9969
Joined: 22 Nov 2013, 20:20
Location: Germany
Main keyboard: Rotation
Main mouse: Roccat Kova+
Favorite switch: Beam Spring
Club member: 0061
 
I think there was one of these on ebay recently
Engicoder

Unread post05 Jul 2017, 19:17

X
Engicoder
 
Posts: 616
Joined: 24 Oct 2012, 14:44
Location: NC, USA
Main keyboard: Leading Edge DC-2214
Main mouse: Corsair M45
Favorite switch: Hi-Tek Yellow
Club member: 0117
 
I think there's one up right now from the guy I got mine from. I think he mistakenly listed it as a 1977 though.

Also, I really don't want to pull the board apart again to get closeup shots of the leafs because they're so delicate, one wrong brush of a hand and you can bend them out of line. But this Digitran pcb I found works the same and has closeups http://www.ebay.com/itm/Milltronics-Par...1863937922? They're just a little leaf of copper soldered at two points above a set of sensing pads that look exactly like those on other capacitive keyboards. The difference is the keyboard one is Z-shaped instead of >.

The plunger shoves the leaf down and increases the capacitance as it gets closer to the pads. That's why the Model F worked with no firmware mods, basically does the same thing as the flipper coming down.

EDIT:Nevermind the ebay link I put there. Looking closer those appear to be Digitran contact leaf, not capacitive leaf like the keyboard. I didn't even know Digitran made a contact version.
Sangdrax

Unread post05 Jul 2017, 19:32

X
Sangdrax
 
Posts: 9
Joined: 05 Jul 2017, 06:50
Location: Acadiana
Main keyboard: Harris 1978 Terminal
Main mouse: Mammoth
Club member: -
 
Engicoder wrote:I think there was one of these on ebay recently

I've been eyeing that one but haven't figured out what CRT it went with. Looks like it has some smarts internally.

Thanks for posting the pics.
snuci
User avatar
Vintage computer guy

Unread post05 Jul 2017, 22:02

User avatar
X
snuci
Vintage computer guy
 
Posts: 983
Joined: 23 Sep 2015, 13:20
Location: Ontario, Canada
Club member: 0131
 
PM the seller. I think when I bought mine he mentioned that he had the CRT's for it too, just didn't list them because the shipping would be so high.

Smarts are bottom board and has a piezo buzzer and speaker that took too much juice to run straight off the controller card unfortunately. There's a three way switch on the right that turns the sound stuff on and off. The chips look mostly like internal memory with a little processing but I can get any pictures you need of the details. I'm more a basic electronic parts kind of guy, once you get past voltage references and shift registers, I get a bit out of my depth.

One interesting thing I did notice was it had some old RN series Dale military spec metal film resistors in it, surprising among all the carbon film and carbon comp stuff.
Sangdrax

Unread post06 Jul 2017, 05:40

X
Sangdrax
 
Posts: 9
Joined: 05 Jul 2017, 06:50
Location: Acadiana
Main keyboard: Harris 1978 Terminal
Main mouse: Mammoth
Club member: -
 
Nice babyblue/turquoise keycaps, really beutiful...congrats again.
Mr.Nobody
User avatar

Unread post09 Jul 2017, 05:30

User avatar
X
Mr.Nobody
 
Posts: 720
Joined: 13 Dec 2016, 10:20
Location: China
Main keyboard: IBM Model M/F
Main mouse: Lenovo Big Red Dot
Favorite switch: Buckling Spring
 
I went ahead and made a small picture of how the capacitive leaf switches in this thing work for the curious. Sorry I wouldn't tear it open a third time but it's crazy how careful you have to be to not bend these the wrong way with them just naked on the board.

Image
Sangdrax

Unread post16 Jul 2017, 03:03

X
Sangdrax
 
Posts: 9
Joined: 05 Jul 2017, 06:50
Location: Acadiana
Main keyboard: Harris 1978 Terminal
Main mouse: Mammoth
Club member: -
 

Who is online

Users browsing this forum: No registered users and 29 guests