For the Robo Camporee in spring 2013, one of my projects was to build an obstacle course for the robots to run. That seemed kind of boring, so I added another feature: a series of targets that had to be shot, in order, with the robot’s cannon. The basic design was rather simple:
- Arduino processor to do the logic.
- Four targets, each with an infrared receiver.
- A big LED display to show the score.
- A power supply to run it all.
Seemed pretty easy and I figured a couple weekends. A couple months later I was scrambling to finish it in time, but it did get done! I had a couple big 5×7 LED displays in the junkbox that I had picked up at the Trenton Computer Festival a few years ago and had been meaning to experiment with. A simple circuit drove it using I2C and a free library. The IR detection was also taken from an open source library, but it did not have the Elenco Titan Tank protocol (no surprise) so I spent some time reverse engineering the protocol and then adding support for it in the library. Two of the tough parts out of the way.
I wasn’t sure if the IR library could support too many receivers at once, so I decided to select one receiver at a time. This engineering short-cut was hidden as “you have to shoot the targets in order… no cheating!” A simple 74LSxxx was wiring up as a 4-to-1 mux to feed into the one IR channel. This was built on an Arduino prototyping shield. There are four three-pin connectors for the IR receivers.
Another problem was that I couldn’t turn on too many LEDs at a time or else the XXXXX driver chip was lock up. It took some experimentation to find out how many at a time could be on, then adjust software not to exceed that limitation. As the score changes, there are various options to transition the new score, none of which exceeds the power limit. Power was easy; a simple little board that connected to a 12v gel cell battery. My batteries are charged by solar panels, so it’s yet another good talking point with the Scouts.
This project seemed like a one-off that would just sit in the basement collecting dust, but we used it again at the Plan B Camporee in October 2013, and my son’s Scout troop wanted to use it and the robots for some winter meetings.