is tricky. Use a pencil for marking; that way, you
can rub out and retry without getting into too
much of a mess.
Take a long ruler and draw lines from the
marks on the outer ring across the pivot center
mark to the opposite side of the outer ring. This
will plot the 6 o’clock to 12 o’clock positions
without having to measure.
The next step is to draw the other rings. On
the 12 o’clock line, mark positions for the other
rings 38 mm apart. Then using the compass,
draw in the other rings at the marked positions.
This should give seven equally spaced rings
(including the outer ring). Use a small punch
and press firmly into the wood to make a small
dent at each LED position; this will help your
drilling to be more precise. Using a 3 mm drill,
start drilling the holes for the LEDs. Once
drilled, sand away the burrs. Now, it’s ready to
be painted. I used two coats of gloss which
took several hours to dry.
Now the wiring commences. The thing to
remember here is when viewed from the rear,
we are working in a counter-clockwise direction.
In Figure 4, the outer ring is shown wired up.
Each ring of LEDs is split in two. Green (LED
Matrix A; see Figure 5) is hands 1 to 12 and
white (LED Matrix B; see Figure 6) is hands
13 to 24.
The wiring connects the LED’s outer ring
anodes together, then connects via current-limiting resistors to the PIC16F877. In this case,
the green is going to port C0 and the white to
port D0 via resistors. On the second ring (next
to the outer ring), the LED anodes are
connected in the same way — via resistors to
port C1 for green and port D1 for white on the
PIC16F877, and so on.
PARTS LIST 1x 3x
16F877 microcontroller 467-1640
DS1307 real time clock 540-2726
ULN2003AN transistor array 436-8451
16-pin DIL socket
8-pin DIL socket
40-pin DIL socket
20 MHz XTAL 672-0306
32.768 kHz 12. 5 pF watch XTAL 547-6979
20 mm coin battery holder 430-675
3V CR2032 coin battery
100 nF ceramic capacitor
22 pF ceramic capacitor
10 µF 35V electrolytic capacitor
4.7K 0.6 watt resistor
10K 0.6 watt resistor
0.6 watt resistors for LED current limiting, value
dependent on LEDs used; my build uses 43 ohm
2x Push to make button switches
169x LED 3 mm high MCD rating diffused; my build
uses 700 MCD 3.6V diffused white LEDs
1x VeroBoard to solder components to
Several meters of 7/0.2 mm wire (white, green,
Some of the parts have RS part numbers available at
www.rswww.com. Other parts come from various
sellers on eBay.Check out www.superbrightleds.com or
www.ledtronics.com for LEDs.
August 2011 29