The project in this article is low
cost and simple to build, while
providing several different light
patterns in random order and
speeds. Each time the circuit is
powered up, the pattern order is
different, only repeating after 65,535
power cycles. Several of the patterns
are random themselves, and the
speed of light change is randomly
selected. Should you want to, it is
easy enough to change the speed
and modify the patterns.
The circuit is built around the PIC16F690 and an eight-channel solid-state relay (SSR) board that is readily available.
The circuit (as shown in Figure 1) is simple enough to build
on a perf board. Configuring the board so it interfaces to
the SSR board was also fairly easy. If you use a different
relay board, then you may have to modify it.
Though I selected the PIC16F690 for this project,
there are many other eight-bit microcontrollers that could
be used. I chose the 16F690 because its port C is eight
bits wide, making it very easy to address as we will see
later in the description of the software; there are enough
other I/O pins to leave ISP and UART available for use,
The SSR board shown in Figure 2 is reasonably priced
and less than the cost to buy the components to build it —
let alone the cost to fabricate the printed circuit board
(PCB). Each channel is optically isolated, fused, has an LED
indicator that is useful when troubleshooting, and is built
December 2014 45
Post comments on this article and find any associated files and/or downloads
■ FIGURE 2.View of the solid-state relay (SSR) board.
■ FIGURE 1.