My son loves building and Lego bricks are some of his favorite toys. He's also the son of a ham radio operator and is absolutely fascinated with radio antennas. For Christmas I built him a model radio tower complete with red pulsing lights and a Lego base.
Sometimes simple analog circuits are the best choice for a project. I often start a project grabbing an Arduino or Raspberry Pi, but this time I reached for the trusty 555 timer. When configured in astable mode it will pulse voltage at a frequency as specified by the chosen RC values. In astable mode, you can make an LED blink at a wide range of frequencies. By chaining the 555 output to a transistor stage, instead of blinking, you get a nice pulse.
I experimented with a variety of values before I ended up with those in the schematic; I felt they gave the most authentic slow red pulse one would see on a commercial radio tower. I also chained a diode before the LED chain to drop the voltage a little bit, which I felt helped the effect.
Each leg of the tower is a 1 foot tall 3/16" diameter dowel I wrapped with alternating red and white electrical tape. The base is made of Lego bricks. I drilled out some circular Lego bricks to mount the dowels and used a little Gorilla Glue to help seal them in place. The top plate uses 4-40 machine screws to hold corner bricks in place. The 4-40 size turned out to be excellent as it fit inside the middle of the circular Lego pieces I used as caps to hide the screws. This design allows the top plate to slide up, for future battery replacement, while leaving the tower in place.
All in all, it was a fun little project I can't wait to give my kid in a few days!
Posted: Dec 21, 2017
Keyword tags: electronicsmake555 timerlegoradioantenna