Tuesday, 20 August 2013

Circuit Board Mystery

Think I've just made a discovery....

I previously commented about my circuit board not looking anything like what's covered in the manual....

The manual describes the interface circuitry using TTL logic chips (7400 series), and all seems relatively simple.

My Armdroid on the other hand uses CMOS (4000 series), includes a 555 timer, has completely different high power drives, and appears overly complicated in comparison.

I happened by chance to read the original Armdroid article published in ETI magazine, Sept 1981 at Alex Zivanovic's excellent website  - and it would appear my circuit board is in fact a "prototype" model

My upper and lower interface boards (click to see full size) pictured when base was opened earlier :

Compare to these pictured (dusty,but still recognisable) :


Alex then mentions he has no other information on this variant.

The article refers to this Armdroid as a prototype and the circuit diagrams accurately reflect my layout and components:

Motor driver interface (see figure 8)

Interface board (see figure 4)

Just how many prototype verses production models exists, or other variants - I don't know!   Doesn't seem to be any other information on the internet about the prototype.

At least I finally have a circuit diagram - will make life a lot easier identifying and repairing that broken track, which is another mystery.

Found this picture of what I think is "standard production" and matches the layout in the manual and blueprints:


This is starting to make a great deal of sense...  I was puzzled for hours trying to figure this out!

You can see there's a big difference between the prototype and production boards.  The power regulator on my model is bolted to the chassis, whereas it's mounted directly on the PCB here.  The 555 timer that provides a manual (not computer controlled) clock pulse, is simply not present on these models.

If you have anything different, please let me know, I would be very interested to see what other revisions are out there!  Better still...  If you have a broken or unwanted production board, I'd be very interested in it!

I also wonder if this makes my Armdroid a little rarer ?

WARNING:  If you open up your Armdroid and have one of these prototype boards do take precautions for handling the static-sensitive devices.  The CMOS ICs are particularly sensitive and easily damaged !