Dispatchatron Junior
Computer Batteries

Image by Rumtopf
As a Christmas present for Japser this year, I made him a junior version of my Dispatchatron. Dispatchatron Senior (www.flickr.com/photos/8190411@N07/6656354727/) was rather large and had to be put in storage when we could no longer spare the space. Dispatchatron Junior, however, can fit in a hat.

In short, the Dispatchatron Junior monitors the computer-voice (no humans) dispatch radio frequency of the county fire department and dispatches a toy fire truck whenever the county dispatches a real fire truck. Even though the radio dispatches are just a computer voice giving addresses and unoffensive descriptions of the problem, I keep the volume just loud enough to be an effect, not loud enough that the boys will start parroting the dispatches.

I was inspired to make the Junior version after seeing a handheld car launcher for sale in Target. The dime-sized car uses a capacitor which is quickly charged (in 5-8 seconds) by two AA cells in the launcher. One button charges the car, and another button levers down a gate, releasing the car.

To incorporate the toy into my contraption, I cracked it open and replaced the charge switch with a relay & transistor circuit to be operated by a microcontroller. I discarded the release button and connecting rod, leaving only the spring-loaded gate. I drilled the bottom of the launcher case and put a tiny eye-screw into the bottom of the gate. I mounted the launcher to the plywood base of the fire station, having cut a slot in the base to allow a string to run from the gate eyelet to a small servo. I then added a small ham radio handy-talkie, a battery case for the servo, a nine-volt battery for the microcontroller, and then the microcontroller itself. The microcontroller is an Arduino Micro that I won in a trivia contest on Adafruit’s Ask An Engineer show. In the future, I might consolidate the various batteries into a single one for easier recharging, though my current system is rather efficient.

I built the fire station out of thin plywood and painted it with a simple mix of kids’ craft paint. I pencilled in brickwork with a white colored pencil and (somewhat sloppily) painted the name of the fire station on the front. The car that came with the launcher was a yellow, rocket-powered, Prius knockoff. I painted it like a fire truck using glossy red and silver craft paint. Neither paint job is perfect, but both are plenty good enough for a two-year-old.

Now the boys’ daily train play is augmented by the occasional excitement of a fire truck dispatch.


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