Model Rocket LauncherI designed and built this model rocket launcher as I was learning digital circuits back when I was a Junior in high school.
I was very priviledged to know John P. Robinson, who was a Professor of Electrical Engineering at the University of Iowa, who put up with my endless stream of questions.
It may now seem crazy to build something this complex with discreet circuitry, but I had not yet heard of a microprocessor and knew nothing about programming. In fact, the Intel 8080 was released later that very same year.
The construction was a bit rough, but hey, I was only 16.
When the launcher was powered on with the key, you first had to enter the hard wired 5 digit password. Then you entered the count down time in hours, minutes, seconds. Next you entered the pad firing order of up to 9 pads which was displayed on the single digit under the count down time. All pads used the same count down time. The four LEDs to the left of the keypad indicated the input steps.
Later I realized you might want to launch more than one rocket at a time. So to support this, just before the next launch you could enter the extra pad numbers to be launched which lit the LED for each pad on the left. How was that for a hack.
The green lights indicated the pad was programmed into the launch sequence. The yellow lights indicated the igniter clips were touching the metal blast deflector which would also stop the count. The red lights indicated the igniter was connected.
I don't remember what the buttons and switches on the lower front do, or were going to do. There is no reference to them in my construction notebook.
Yes, this launcher was over-kill, but it wasn't really about launching rockets.
When this project was almost complete someone suggested that I should enter it into the science fair.
When my chemistry teacher gave me the entry form he told me he didn't believe in science fairs because they were just a bunch of gadgetry, and he didn't know anyone that had ever won.
So I entered it into the Eastern Iowa Science Fair and won first place in 1974. This meant I was entered into the International Science Fair, which later became the Intel Science Fair, where I won third place in the engineering category.
All logic was 7400 series TTL. The 74LS parts did not become available until two years later.
The only test equipment I had was a volt/ohm meter and an LED. Signals had to be slow enough so I could see they were happening.
All boards were hand soldered point-to-point with 24awg wire. The edge connectors were "stick-on" which were very unreliable and caused me no end of grief. I had a lot to learn about reliable construction techniques. It was not as easy to find parts back in the days before the Internet either. Countdown timer board