Propeller Clock

Topics: Light-emitting diode, Microcontroller, Interrupt Pages: 15 (2515 words) Published: January 16, 2010
"Propeller Clock" Mechanically Scanned LED Clock
Seven light emitting diodes spin, giving the illusion of numbers in the air

An Overview:

Top ViewSide View

How this clock works:
A motor spins the "propeller", and a small microprocessor keeps track of time and changes the pattern on seven LEDs with exact timing to simulate a 7 by 30 array of LEDs. It is an illusion, but it works nicely.

To build this clock, few things are needed, including:
1. Skill with motors and mechanical things.
2. Prior electronic experience.
3. A dead VCR or floppy drive or other source of a suitable motor and miscellaneous parts. 4. A programmer that will program a PIC16C84 or 16F84 microprocessor. Schematic Diagram:

The Propeller Clock Parts List:

1. Capacitors:
• C1, C2 - 33pf ceramic
• C3, C6 - 0.1uf ceramic
• C4 - 47uf electrolytic
• C5 - 47,000uf supercap(memory cap)

2. Diodes:
• D1-D7 - light emitting diodes
• D8-16 - 1N4001 general purpose 1amp rectifiers

3. Resistors:
• R1 - 120 ohm DIP array or seven 120 ohm resistors • R2-R6 - 10k ohm

4. Misc:
• J1 - three terminal Berg connector
• SW1-SW3 - normally open pushbutton switches
• U1 - PIC16C84, PIC16F84 or PIC16F84A
• XTAL1 - 4MHz crystal

Note: U1 to be programmed with mclock hex file

A full description how to build it:

Step One: Mangle a Motor:

Find a VCR, perhaps a Sharp or a Samsung, with a flat reel motor. The motor I have is marked JPA1B01, but Sharp knows it by the number RMOTV1007GEZZ. Take it apart without mangling the brushes (there are little holes to slip a paperclip into to move the brushes out of the way), and notice that it has one ball bearing and one sleeve bearing. Knock the sleeve bearing out of the case and glue or solder it to the other end of the motor, as an extension of the ball bearing. The shaft of the motor will have to be repositioned slightly to get the right height, press it in a vise with a hollow spacer on one end. Take a Berg connector with three wires and solder them to the three terminals on the motor's armature. Glue a short threaded spacer to the shaft at the end that will stick out the hole, and reassemble the motor(be careful with the brushes). You can glue the motor to a VCR head as a weighted base.

A drawing of the modifications to the motor:

Step Two: Build the circuit:

I used perfboard (Vectorboard) and handwired the circuit together. Use an 18-pin socket for the 16C84 because it needs to be programmed before putting it in the circuit. For the 7 current-limit resistors I used a DIP resistor array, because it made it easy to experiment with LED brightness. I settled on 120 ohms. You can use seven regular resistors, because 120 ohms works fine, though it puts the peak current right at the limit for the 16C84. Think about balance while you build this circuit, and reference my pictures, so you don't have to add a lot of balancing weight later. Substitute for any part values you like. Note that I used a 47000uf supercap, it is to keep the clock running after turning it off, so you can set the time. The LEDs get power separate from this. Don't substitute a ceramic resonator for the 4MHz crystal, this is a clock and should be accurate.

Step Three: Program the 16C84:

You'll need a programmer that will program a PIC16C84. If you found this file/web page, you can find plans to build a 16C84 programmer. Program it using the hex file accompanying this document. I have included the source code(.asm) just for your amusement. When programming the chip, set the chip options to: watchdog timer(WDT) OFF and oscillator to normal XT crystal.

The hex code ready to load into a PIC16C84 or 16F84 chip:

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