[vcf-midatlantic] A little electronics hack

Evan Koblentz evan at vcfed.org
Sun Sep 29 11:49:12 EDT 2019

Yesterday at the workshop I took out the Laser 128 and circa-1987 Lego
electronic parts. They'd been packed away since Maker Faire last year.

My new robot barely worked, despite being almost identical to the old robot
and running the same software.

I found a loose wire connector which Ian fixed. Still had a lot of problems.

Neville (a retired EE who first joined the old MARCH group in the mid-2000s
and recently came back) started testing things with a meter and scope. He
figured out that some of the interface box outputs were only producing half
their usual power.

We opened the box (a couple of years ago I swapped its plastic rivets for
screws). Nothing seemed wrong. It was clean and all of the capacitors
looked good for 30+ years old.

Neville noticed something that I wouldn't have. The circuitry contains a
safety mechanism to shut off all power if the current jumps too high, such
as a kid inserting a paper clip. There's probably a technical name for that
but I do not know it. Anyway, for unknown reasons this circuit was kicking
in! He jumped it with an equal-length wire. :)

We tried the robot again. What a difference! Even before it stopped working
last year, the motors always seemed kind of weak. I just assumed that was
normal because I never knew it any other way. Now I see what normal is
supposed to be. The motors run MUCH stronger! It's an amazing improvement.

Neville also resoldered a loose LED connector and one suspect cold joint.

So I'm a happy camper. The electronics for this set are running better than
ever, which means I can focus on the Lego side and the software.

I'm giving a big presentation about all of this Lego stuff on Friday, Nov.
1 at Brickfair NJ and then exhibiting it there Saturday and Sunday. Now I
do not have to worry so much about the demo aspect failing.

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