Analog Computer (Heathkit EC-1)

[RDR10]

Hi,

I am looking for someone that owns an analog computer or at least has some details about one, the main goal for me is to replicate it with modern parts and donate it to a local museum for vintage computers. I would like it to be as close as possible in appearance with the original.

My first intention was to replicate Heathkit HC-1 but is not that easy to figure out all the dimensions from pictures.

[Phil_G]

Just a suggestion, I've done similar and I've found that because a museum display is static, untouched, that actually a visibly-accurate, animated mock-up is better, one that appears to the casual viewer to be very busy on a problem, with moving-coil meters swinging, knobs rotating, indicator bulbs fading up and down, a 'ding' solenoid bell, an internally-looped chart recorder...  you can even coordinate a dangerous prediction with meters and chart recorders bouncing off their end-stops with red lights throbbing...
Participation is good, you could give them one nice strong pot to turn against a dial labelled 'radius' and have it show 'area of the circle' on a meter.  Feed a pot into a comparator and get them to try so set the output mid-way (which of course they can never do but it amuses them to try!) then explain its operation and where it would have an application.
Present Joe Public with a perfect replica of a Heathkit HC-1, in a glass case, doing nothing, and they will glance and move on.  Give them an animated or interactive display and they shout their kids over to see it...
Its rather like the animatronics that attract customers into those amazing German Christmas stores, but applied to demonstrate history and the technology of its time.
As I said, its just a suggestion, based on our own presentations.
Cheers
Phil

[granzeier]

Phil has some great ideas for a museum exhibit. On the other hand, if you do want a real, working, analog computer, Practical Electronics had a nice one starting in their September 1978 issue.

https://worldradiohistory.com/UK/Practical-Electronics/70s/Practical-Electronics-1978-09.pdf
https://worldradiohistory.com/UK/Practical-Electronics/70s/Practical-Electronics-1978-10.pdf

Then in November, they started showing how to "program" the computer. There is even a "program" to let you play "Lunar Lander" on this thing. 
https://worldradiohistory.com/UK/Practical-Electronics/70s/Practical-Electronics-1978-11.pdf
https://worldradiohistory.com/UK/Practical-Electronics/70s/Practical-Electronics-1978-12.pdf

And, if I remember correctly, there may have been one, or two, other follow on articles about the computer later on.

I have always been interested in this project, but I have too many other things going on right now. 

[RDR10]

Hi Phil,

For sure this will be a functional one, my intention was to make one that is also robust, there are a lot of kids and students visiting the museum and for sure needs to resist those little gremlins poking, pulling and twisting the knobs.

[RDR10]

I have always been interested in this project, but I have too many other things going on right now. 

I also have some unfinished projects haunting me  but somehow I realized that this kind of project will also serve others in the long run. Kids nowadays have no idea how the computer industry started and even less how difficult was in the past to get a computer.

[ebastler]

Computer museums vary a lot in their concepts -- from "walk-through exhibits for the masses" to "in-depth, hands-on interaction for small groups". A working analog computer could cater to both audiences, I would say:

• For casual visitors, you can always pre-wire the computer to run some repetitive job which creates nice graphics on an oscilloscope. Put a transparent cover over the plugboard and critical settings which you do not want the visitors to mess with, leave other knobs accessible for some limited interaction.
• For in-depth demonstrations or interactions, it is a bit awkward that you cannot easily "save" a program, but will have to re-wire it every time you want to show something new. But as long as you keep the demos simple, that is feasible. (There were some analog computers with removable plugboards, so you could swap in an entirey pre-wired program. But I would not recommend this for a rebuild; the many-pole connectors are probably prone to contact problems.)
  

To clarify: I assume you are interested in the Heathkit EC-1 (not HC-1)?  Updating the thread title and your first post might help to get more replies on that particular model.

The manual for the EC-1 does state its overall dimensions (on page 35 of the PDF, https://www.ccapitalia.net/descarga/docs/1959-ec-1-heathkit.pdf). Together with the available photographs, e.g. in this restoration story (https://www.nutsvolts.com/magazine/article/May2016_Heathkit_Restoration), it should not be too difficult to get the components and their positions about right. Which details are you struggling with in particular?

[TimFox]

When I was an undergraduate (late 1960s), one of the physics professors programmed a Heath analog computer (I don't remember the model) to do a bouncing ball.
The result was displayed on an X-Y CRT (using a Tektronix 503 CRO).
A constant-radius circle was generated to be the ball, and these signals were added to the X and Y voltages:
X voltage:  a serrasoid ramp gave the center of the circle  a constant velocity in the X direction, and the X voltage reset to the left after reaching a maximum on the right.
In the Y direction, the altitude followed the equations for gravity and a finite-fraction loss of energy at each collision with the ground.
The negative voltage limit on the Y voltage caused the bottom of the "ball" to flatten when it hit the ground.
This system was left running on display in a glass-faced cabinet in a corridor.

[ebastler]

When I was an undergraduate (late 1960s), one of the physics professors programmed a Heath analog computer (I don't remember the model) to do a bouncing ball.
The result was displayed on an X-Y CRT (using a Tektronix 503 CRO).

The restoration report I linked to above shows that exact demo (including wiring instructions). Should make an excellent display for casual visitors, or a starting point to explore deeper for those who want to spend more time.

The photo of the fully wired panel also reinforces the point I made earlier: If you let visitors mess with the wiring, be prepared to spend time regularly to put it back in place. 

   

[Tom45]

I have a Heath Kit EC-1 that I bought and assembled when I was an EE student in the 60s. Not sure what shape it's in now but I'd be glad to dig it out and help you.

[RDR10]

I have a Heath Kit EC-1 that I bought and assembled when I was an EE student in the 60s. Not sure what shape it's in now but I'd be glad to dig it out and help you.

Hi Tom,

Based on components that I found  with different suppliers there is a chance that some parts will have to be replaced (sockets, knobs, etc.), what I would need is a picture with a measuring tape placed across the panel (in a couple of places) to figure out how close are things and how much space I have for small changes. I realized looking for parts that some are not available anymore and would have to be replaced like the double (brown) socket.

I would like to do that before ordering  200+  4mm sockets .

@ ebastler, thank you for the correction, subconsciously  I was thinking at H1 but I really meant EC-1.

[ebastler]

I realized looking for parts that some are not available anymore and would have to be replaced like the double (brown) socket.
I would like to do that before ordering  200+  4mm sockets .

Those brown sockets were originally meant to hold crystals, and the HC-1 used them to hold resistors and capacitors (in custom holders provided by Heathkit). These are smaller than 4 mm -- the Nuts & Volts restoration project mentions that pins from octal tube sockets were a good fit, i.e. 2.4 mm pin diameter.

Miniature plugs and jacks with 2.6 mm pin diameter are still commonly used for toys (model railways, doll houses), and should be a good fit size-wise. Called "Zwergstecker" in German, and apparently just "miniature plugs 2.6 mm" in English. They work alright -- the plug contacts are split and have a bit of spring action, while the jacks are rigid tubes.

Sockets in two-pole configuration are available, but don't look right for the HC-1. So you would still have to do some 3D printing and cannibalizing of off-the-shelf sockets to make nice replacements for the HC-1 crystal sockets. But that would give you sockets of the right size which accept an off-the-shelf plug.

[RoGeorge]

See the book and the links from this topic:
https://www.eevblog.com/forum/programming/lets-bamboozle-the-software-devs-computing-amplifiers-book-from-1966/

[Tom45]

@RDR10

It will be a day or two before I can get my EC-1 out and set up for photos.

What museum are you working with?

[RDR10]

@ ebastler
I would prefer to go with COTS products, I noticed that when there is a lot of customization, projects tend to take longer to complete or they become dead....ish.

@Tom
No worries , most of the time dedicated to this project will be during weekends. The museum is owned by a private collector who (unlike others I know ) decided to make his passion public and now he managed to rent a place and display most of his collection of computers produced and designed in my country between 60's and 90's, amongst the usual candidates from US, England, France, Germany, etc. you can check the links below.
For now it is only in one language but with some support I hope this will be translated into English as well.

https://retroit.ro
https://www.facebook.com/retroitmuseum/?locale=ro_RO

[ebastler]

@ ebastler
I would prefer to go with COTS products, I noticed that when there is a lot of customization, projects tend to take longer to complete or they become dead....ish.

Makes sense; it is a complex project already. You can use two individual off-the-shelf 2.6 mm jacks instead of the dual jack, if you don't mind the different appearance. The size would still be "more correct" than if you were to replace them with 4 mm jacks, and there is less room for user error if you use two different types of jacks on the front panel.

https://www.reichelt.de/de/en/miniature-panel-jack-2-6-mm-blue-ebv-26-bl-p7307.html

[RDR10]

Makes sense; it is a complex project already. You can use two individual off-the-shelf 2.6 mm jacks instead of the dual jack, if you don't mind the different appearance. The size would still be "more correct" than if you were to replace them with 4 mm jacks, and there is less room for user error if you use two different types of jacks on the front panel.

https://www.reichelt.de/de/en/miniature-panel-jack-2-6-mm-blue-ebv-26-bl-p7307.html

I haven't thrown the towel in just yet on the brown sockets, a colleague of mine has a 3D printer (and knows how to use it) and offered support, by the end of next week I should have a couple of samples with 3mm plugs, if they look ok I might do it otherwise I will go for the 2.6 mm sockets.

[Tom45]

Finally dug out my EC-1 and cleaned it up a bit.

Here are some photos of the front panel.

[Tom45]

And two photos of the interior.

[RDR10]

Hi Tom,

Thank you for the pictures, it is going to help me a lot selecting components and drilling holes. Hopefully in 3-4 weeks I should have the front panel assembled.

[TimFox]

Looking at the interior shots:
Many here would recommend replacing the old aluminum electrolytics.
From my experience with other equipment of the same vintage, I would definitely replace all the paper capacitors with modern polypropylene or polyester units, since the non-hermetic paper units have probably absorbed moisture.

[RDR10]

After some effort from my two left hands and almost nonexistent metalworking skills I bring you the front panel. The rest of the housing will have to be made and the electronics too.

I can't really say I'm satisfied since even a blind person could have drilled a straighter series of holes plus I made some mistakes here and there , and I still have to find a good method of printing the markings on the panel.

L.E. There is some distortion from the camera, that cannot be attributed to my lack of metalworking skills.