Rotating Aircraft Beacons

		The American Flyer and Marx aircraft beacons were based on a simple principle. Hot air from a bulb vented through vanes in the top of the beacon and caused it to rotate. Unfortunately, the original GE 465 "Dimple" bulb was rated at 14 volts but run at about 18 volts to generate more heat. This caused it to burn out frequently and it was so hot it would soften the plastic of the tower and cause it to deform. If the top beacon fell off and touched the bulb, it would melt the lenses. So using an Arduino pro-mini and a commodity servo motor, I am going to attempt to modify a Marx tower to have the motor turn the beacon top and LED's light it. This should provide realistic action but no heat and much lower current draw.

	Here is a photo of a Marx beacon that has been damaged by the heat from the bulb. I plan to sand the top flat and install a small ball bearing race in it to allow the rod to turn the beacon top smoothly.

Here is a photo of the Arduino pro-mini and the ULN2003 driver chip mounted on a small piece of perfboard. The servo motor is a 28BYJ-48. It is a small 5 volt servo commonly used in Air Conditioners to wave the vanes up and down. Because they are made by the hundreds of thousands, they are available from many sources for under $3 each. I bought a package of 6 of them on Amazon for $12.99 and they came with the driver board which is the source of the ULN2003 chip I used. The motor has an integral gearbox that steps the speed down to about 1/64th of the motor speed. This increases the torque and if you choose the "20" set speed setting in the sketch below, it will turn about 10 times a minute which seems about right. Here is the CODE for the Arduino.

Here is a photo of the completed project. Initially I tried to power the LED's using the ladder for the negative side and the motor and shaft for the positive side. Unfortunately, because there are some bearings involved, it flickered quite a bit. I ended up using the ladder as negative but added a wire hidden behind the ladder as the positive for the LED's. That solved the flicker and the brightness is pretty good, not as bright as the original dimple bulb but plenty bright enough to be seen in regular room lighting. The arduino and driver chip are hidden in the little black box. I might detail it to look like some sort of electrical panel. The whole thing is powered off a 5 volt USB 1 Amp cell phone charger. It would be easy to create a simple circuit that would take the 18 volts AC from the standard Gilbert transformer. rectify it and drop it down to 5 volts DC. There are a lot of little modules available from Chinese suppliers on eBay that lend themselves to doing things like that for a couple of dollars. This is an older version using a Marx beacon. I ended up making a different version using a broken American Flyer 769 beacon and designed a new board that incorporates the rectifier and regulator so it will run off the standard 16 VAC transformer. A link to an early Youtube video where you can see it in operation Here

	New pc boards incorporating the buck convertor and bridge rectifier so they can run off standard transformer voltages. Rather than using an Atmega 328P chip and the support circuitry, I just used a whole Arduino Pro Mini. Again these are trivially cheap on eBay, about $3.50 I think.