Testing Interface A / 9750 without a computer or software

[evank]

Recently, a few people found my website (www.brickhacks.com) and asked me how they can test set 9750 ("Interface A") if they don't have a suitable 8-bit computer and/or the necessary software. I thought that was a good question, so I asked @Toastie for help. He devised a method based on the pinout of the device's parallel connector. But in a nice coincidence, he's a chemistry professor and I work as a university science writer, so I thought it best if I do my thing and translate it from geek-speak to plain language. 

Thus, he and I present to anyone who's interested: how to test Interface A without a computer.

https://brickhacks.com/testing.php

Feedback is welcome.

[Lego Tom]

I get a "Dangerous Website Blocked - This is a known dangerous site." from Norton when I click on your link.

Edited November 4, 2023 by Lego Tom

[evank]

I can't explain that. 

[Carsten Svendsen]

Anti-virus software is so last decade. Don't have it on your computer and don't click anything on sketchy sites. Adblock is all you need.

Just read through it, and without the device in my hand, I find step 6 fairly confusing, maybe some pictures would help tremendously

Edited November 5, 2023 by Carsten Svendsen

[evank]

Which part confused you?

PS. I'm planning to make a video. 

[Toastie]

On 11/4/2023 at 2:47 PM, evank said:

chemistry professor

Chemistry rules

Very briefly: Maybe the term positive/negative "port" is confusing in step 6 @Carsten Svendsen? If so, "port" relates to either the "test" (=permanent 4V DC) output of 9750, located at the top right, or to the two terminals of any 3 - 5V DC power source at hand.

Also, it is rather important in step 4 to figure out, which hole of the test output of 9750 is positive and which is negative, as it won't work when wired the other way around. On the two 9750's I have, the negative hole is the upper, and positive the lower. I also believe that his is the case on all 9750's - but who knows.

@evank You may want to point to the polarity significance in step 4. And maybe change "port" to "positive test supply voltage"? Don't know ...

Best,
Thorsten

[evank]

I thought it didn't matter. Will do some more experimenting this week. 

[evank]

@Toastie, you're correct! I didn't know it, but when I tested your method the other day, there was a 50/50 chance and I happened to have the plug in the right direction. :)  On the test port, the top hole is indeed negative and the bottom hole is positive. I will update my write-up.

@Carsten Svendsen, I will break part 6 into multiple steps and add more pictures.

Edited November 6, 2023 by evank

[WhitneyDesignLabs]

Hello. I am introducing myself. My name is Scott. Evan suggested I look at this forum. My interest here is mostly in the Lego interface A 9750 and the Apple II computer. As a kid we had an Apple ii+, and I built several robot arms for science fair projects. I always wanted to control the robots with the Apple, but was never able to accomplish this in the 80s. Now (2023) I am revisiting this project again with a new robot arm, and recently acquired retro computing stuff.  I don't want to hijack this thread, so I will follow it from here. Just wanted to say hi, and this seemed like a good place to do so.  Cheers, Scott

[Toastie]

Hi Scott,

welcome to the club!!!

There are a number of threads in this forum dealing with 9750, I guess you have seen them already.

Are you planning on some DIY interfacing, or do you have everything in place already?

All the best and have fun!
Thorsten

[WhitneyDesignLabs]

Danke schon, Thorsten! @Toastie  I just tested my 9750 using your method and @evank's write up. It worked perfectly. I used the "always-on" connections in the Interface A for my test voltage, even though I had a bench top supply on hand. As a testament to robustness, I accidentally grounded out pin 3 briefly. It complained a bit by turning off the power light and squealing mildly. I quickly recognized my error and move the ground jumper to pin 5, and proceeded to test all the 6 output ports and the 2 input ports.  All worked perfectly.

I plan to build a DIY Peripheral card for the Apple IIe, based on the schematics, while I keep my eye out for a cheap authentic Apple card in a cow's track somewhere.  I will actually most likely build two (or more) of these for additional i/o.

I will build my own interface/translator from the 9750 into modern electronics. The plan is to control my modern-ish robot arm. However, that robot arm is stepper motor powered, therefore, some some electronic trickery may happen on a little translation circuit. (for rough movements approximating precise motor steps.) Or.... I may build another robot arm using DC motors only, and go with more period correct approach. (i.e. doing what I would have done in the 80s had I known about this interface stuff). Not sure which direction the project will go. Might go in both directions simultaneously. The whole thing is an learning and exploration project for me, and maybe can be used as an educational tool as it progresses.

Edited November 12, 2023 by WhitneyDesignLabs
Tagging Toastie

[evank]

Welcome to the fun house. 

[Toastie]

39 minutes ago, WhitneyDesignLabs said:

The whole thing is an learning and exploration project for me, and maybe can be used as an educational tool as it progresses.

And that's the core of the matter! Just make sure to let @evank know about your endeavors and maybe post here (this is what I try to do; Evan runs his wonderful website pulling everything together, documenting all these activities. EB is (for me) the place to "document" details, nifty things, fun doing it, and letting the world know what they miss(ed) . Says the dude, who gets zero to a couple replies on respective threads . I sure let Evan know though what I am up to).

Oh yes, as Evan said: Welcome to the fun house!

Best,
Thorsten