Day 98: Fog and Sparks

I’m back in town and oh, there’s so much to catch up on. Spending time with good friends, disabling a smoke detector, crashing face-first in a blinding sandstorm, giving the robot its first test run, and acquiring a fuzzy pink hat. So here we go.

Let’s wind the clock back a few days.


Woke up to crazy-thick fog. The car’s in the shop, so it’s a good day to wander out without one. I’ve got a few stops to make, and one of them is to get some parts for Secret Plan 187.

First, there’s time to kick the day off with a stop at the Chestnut Street Coffee Roastery.
There’s an excellent bar where you can sit and have breakfast and coffee. San (the owner) knows everyone here by name. He remembers what they like, and won’t hand you a drink unless it’s perfect.

By midday, it’s turned warm and sunny.

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This is the finished result from the demon stamp-o-matic machine. Walking across it makes your eyes go woogity, but that’ll probably get better over time as it gets grubby.

This product wins the “least appetizing packaging I’ve seen all week” award. Competition was tight, but the white syringe on the side pushed this one up for the win.

SP187 calls for four very small motion detectors. The Radio Shack on Market St. just happens to have exactly four, so the decision is made.

Back at home, it’s time to get to work.

Casual robot building goes a lot faster if you start with a working mechanical base, and then add sensors and a brain. Toys are usually the best place to start; they’re inexpensive and wacky.

The Motor Ball is a radio-controlled toy from the early 1990’s. This one doesn’t work. It broke 5 years ago, and I meant to throw it out, but forgot.

Opening it up, we get to see what’s inside. Surprise… wires and gears!

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The cat has decided that I’m ignoring her. She’s right.

She’s trying to hypnotize me and steal my robot parts.

…so with everything stripped off, here are the basic parts. There’s a radio circuit, some power electronics, a pair of motors at the bottom, and a bunch of gears.

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One of the gears is about to go skipping across the floor. (sigh)

If you like tinkering, but also enjoy being married, put newspaper between your project and the dining room table. Really.

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I’m not allowed to sit down until I give her something to play with.

The first thing to do is figure out how to drive the motors. I don’t know anything about this circuit, so some things need to be figured out by trial and error (and error). There’s one main logic chip, with a bunch of pins soldered into the main board. One of the pins is connected to the ground wire.


To find out more, I power up the circuit and touch the pins one at a time to ground, to see what happens. Nothing at all.

Now for the opposite (and more risky) test. With the circuit still powered up, I connect each pin to the 6-volt power source. This is just like figuring out how a watch works by hitting each tiny gear with a large hammer to see if the hands move.

The first pin I try sends sparks flying. Whoops.

Further down, I finally get a hit. One of the motors goes “rrrRRRRRrrr,” and the cat comes running over to watch.

It turns out that there are four pins which control the motors, so I make some notes.


I’m ignoring her again. Crunch crunch.

The new motion detectors I bought will be the robot’s “eyes” and need to be located close to each other. This circuit’s physically tricky to build, and is not going to work on the first try.

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She thinks the second attempt is the best one for batting around the room.

It’s time for a break, just in time to run down to the Castro Theatre. They’re showing Gentlemen Prefer Blondes, which I’ve never seen.
It’s excellent. I’ll bet some of the funniest parts probably weren’t quite as funny in 1953 as they are now. The audience is fun, and loves it from start to finish.

Random assertion: Lab assistants should be chosen carefully. Pick one you enjoy spending time with, and the rest will take care of itself.

Steganographic data: 1822/4.8

Days remaining in Secret Plan 158: 11

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