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Don Zehnder's Analog and Digital Version of the Bob Blick Propeller Clock

This clock is based on Bob Blick's original propeller clock

Since a few people have expressed some interest, I thought I would provide some details on the versions of the propeller clock that I have made.

My propeller clock is totally brushless and is very quiet and smooth. The motor is salvaged from a squirrel cage fan. Ample power is provided to the clock using a rotary transformer arrangement which is simple to implement. Another difference from Bob's original clock is the you set the time on mine while it is spinning. A Hall-effect sensor is provided for this purpose. One just holds a magnet near the spinning clock to advance the time. Another Hall-effect IC is used to switch between display modes while the clock is running (using the other pole of the magnet used to set the time).

The "rotary transformer" is made from some coils that I salvaged from junk.
Here is a sketch of some of the details  (see also Chester Lowrey's for the transformer coils)

Schematic for the clock and rotating part of the power supply

Schematic for the fixed part of the power supply

Here are some pictures of key parts of it


Here is the source code for the PIC16F84 processor that is at the heart of the clock.

3/29/01 (Slightly)Improved! Source code for the analog and digital clock

5/01/01 Wobble Fixed!!!!
It seems that several people have actually built a version of the analog and digital clock from this web page. Any of you who have successfully completed the clock will have noticed that the hands of the analog clock are unsteady. This has bothered me as well, but never enough to really think through the problem. For some reason I have recently become interested in improving the code to fix it. While I am not going to go into detail about why the hands wobble in the original version, I can report that I have conquered the problem. The solution, for now, is a rewrite and very minor rewiring of the hardware to accommodate the Ubicom (Scenix) SX18AC processor. The SX18AC is nearly, but not quite, a drop-in replacement for the PIC16F84 for this clock. The SX18AC can be clocked at up to 50MHz, but I have kept the oscillator at 10MHz. The advantage of the SX18AC is that it executes one instruction per oscillator cycle (instead of one instruction for four clocks for the PIC). In this clock, therefore, four times as many interrupts are generated per revolution of the clock. This, and another reorganization of the code, allows the hand position to be determined more accurately, resulting in much less wobble. It really does work, and I would recommend this update. A couple of things to note:

SX18AC has only four portA pins, so the part of the circuit connected to PortA,4 has been moved to an unused pin of PortB.
Since the SX18AC has optional pull-up resistors on all input pins, one could omit the external pullups that are on my schematic
The SX18AC draws more power. I had to increase the voltage to the fixed drive coil circuit a bit and increase the value of the resistor for the outermost LED in order to get stable operation.

OK, so maybe you want to give it a shot?
You will need:
An SX18AC programmer and software
My SX source code (see comments for the minor rewiring required) and include file, for assembly by Microchip's MPASM

If you don't like the wobble, but hate the idea of the tiny bit of rewiring and the hassle of figuring out how to program the SX18AC (it took me a while to figure out how to do), there is hope! Send me an email if you would like to see PIC16F84 code for 20MHz that incorporates the wobble-reduced algorithm. I have not yet done this, but it should be quite a bit better than the current 10MHz PIC version. A crystal change would be required though and some of the power supply issues could also appear.

Other prop clocks:

Luberth Dijkman's version of the propeller clock. He made his analog version using my code but made some very nice improvements to the appearance of the analog clock with the outer LED for the outline and inner LEDs to extend the hands to the center.

Chester Lowrey's rotary transformer/brushless clock features
elegant mechanical design. Check it out

Daryl Bender's well-crafted "Aerobat"

An earlier version of my clock and a JAVA simulation of the same