I have a POV toy/sign I got from thinkgeek.com, I don’t think they sell them any more… Anyway, I accidentally broke mine, and decided to fix it by making a new “propeller.” I did the layout design in a CAD program running on Linux program called qCAD. I etched the board fairly easily using the Pulsar Profx “Contact Etch” method.

The contact etch method is pretty cheap and the only supplies needed are etchant, gloves, a sponge, a big glass casserole dish, green TRF, toner transfer sheets, an iron, and a laser printer. I’ve been pleasantly surprised by the level of detail/trace widths I’m able to reliably etch using this method, 0.25mm(~0.01in) trace widths in this case. The only problem I had initially was getting the toner to stick to the copper. I wasn’t using enough heat/pressure, so I cranked the clothes iron’s temperature knob the way up and applied more pressure for a longer period of time. After doing this, the toner transfered very well. Another minor issue I’ve run into is that the green TRF sometimes creases and the plastic doesn’t transfer to the toner in that spot. I end up just touching up these spots with a sharpie.

The propeller uses 9 LEDs to display 6 messages each up to 16 characters long and runs off 3 AA batteries. I’m not sure what kind of microprocessor it uses as it’s covered in epoxy, it does look like there might be some pads to program/reprogram the microprocessor. I thought about connecting another uC to a computer and then to the propeller, but the link between the uC and the buttons aren’t reliable enough.

Things I could have done differently:
Shorten the wires by soldering to the circuit board first, attaching the propeller to the motor shaft, then soldering the wires to the propeller. With shorter wires it would have been a bit easier to balance, and been a much more durable and clean install.

If I had a scale I would have measured the weight of the LEDs so I could better approximate the weight needed to balance the propeller. The weight I added was a little too heavy so I compensated by adding a little bit of hot glue to the other side. Hot glue is a pretty lazy way of fixing the problem, typically I can’t stand hot glue, but I digress…

Etching pattern (DXF file)

This was a proof of concept of sorts, just an LED attached to the circuit board using magnet wire. In this photo you can see the springs that provide power, timing signals, and user input.

Toner etching pattern transfered to copper clad board, next to the toner transfer sheet

green TRF has been applied, crease visible on left hand side

peeling green TRF off

green TRF removed laying next to circuit board

Circuit boad with green TRF applied

top side of control circuit next to new propeller circuit board before etching

bottom side of control circuit, note the rings, these are used in conjunction with the springs to supply power (outer ring Vdd, middle ring GND), timing signals (small trace on right hand side that runs parallel to the middle ring and then half way into the middle ring), user input (innermost ring, this ring would have the least electrical noise) to the control circuit.

control circuit sitting on top of new propeller

soldering magnet wire to etched circuit board

soldering wires to circuit board

propeller displaying 16 characters, a tripod would have helped here…


used flash to show propeller and message, note propeller spins counter clock wise (CCW)