Microelectronics | Magic Wand

Synopsis

Searching through my parts bin, I've found a few violet LEDs. I've been thinking about possible uses for them, and finally, my conclusion was that I could design a magic wand. While there is no real magic involved, the virtual display created by waving the wand left and right is entirely based on the persistence of vision phenomenon of the human eye. The result is that those seven LEDs will simply draw letters in the air. The letters are stored in the microcontroller software as 7 x 5 matrices, similar to ASCII characters stored in the video ROM BIOS on IBM PCs and compatible.

I have designed a simplified schematic diagram so that it can be included in a transparent plastic case that looks like a wand for easy wielding. The message stored in the EEPROM appears whenever the wand is waved left and right with a certain frequency. The microcontroller scans the LEDs and, in conjunction with the oscillatory movement, produces visible scrolling characters in thin air... pure voodoo.

Schematic Diagram

As I said, the schematic diagram reveals a PIC microcontroller and seven LEDs connected directly to the MCU pins of PORT B, configured as outputs.

Fig. 1: Electrical Principial Schematic

Fig. 2: Bottom Layer Printed Circuit Board

The core of the circuit is the PIC16F628(A) microcontroller. This can be replaced with a PIC16F84(A). The simple RC oscillator is built around a 12 kΩ resistor and 10 pF capacitor. The ASCII characters are obtained through a software time multiplexing technique. JP1 can switch between two different stored messages.

The circuit is powered from a 9 V (alkaline) battery. To obtain the 5 V required by the microcontroller, I have used a linear voltage regulator of type 78L05.

Software

Here is an example compiled software program that displays some sample preprogrammed messages, good to test the wand. With a little bit of creativity, you could program your own software for this magic wand in C or Pascal if you don't want to go the assembly language way. For sure, this would be a great learning project.

bagheta.zip (archived .hex file)

The JP1 jumper configuration is listed below.

JP1 = ON: Message = Salut (Hello in Romanian)
JP1 = OFF: Message = Hello

Construction and Pictures

I've made the PCB at home with the toner transfer method. Then, I've etched the copper with ferric chloride (FeCl₃). Finally, I've cleaned the toner with a mixture of acetone and isopropyl alcohol.

This is the solder side.

This magic wand could either be a veritable present for somebody dear (which was exactly my use-case), or it can be built as a form of amusement. Or even as a learning project for kids, and beginners with PIC microcontroller programming.

Thank you for reading this page, and I hope you found it useful.