was arranged so it would easily interface to the SSR board.
The input terminals of the SSR board are spaced 0.2” for
all eight channels and ground. I used 17 positions of a
right angle male 0.1” header; keeping the outer pins, I
removed every other pin so nine 0.2” spaced pins were
left. I soldered the shorter pins on the edge row of the
perf board, with the longer pins extending out from the
board so they could mate with the SSR board. This takes
care of the connections for channels 1 through 8 and the
ground connection. Next, wire the header pins to the
appropriate pins on the microcontroller. The completed
microcontroller board is shown mated to the SSR board
in Figure 3.
Looking at the microcontroller board in Figure 4, you
will notice pins for ICSP, Rx, and Tx for future use or for
modifying the program; these pins are optional. I used a
socket for the microcontroller with the decoupling
capacitor, C1, mounted between the two rows of the
socket beneath the socketed microcontroller. This allows
the capacitor to be very close to the Vcc and ground
leads while taking up less space. The only other
connection is a male two-pin header for power, fed from a
five volt wall wart supply.
Using the prebuilt SSR board makes wiring the high
voltage mains circuitry easier and safer. Even so,
precautions must be taken to make sure polarity is
maintained; there is no exposed high voltage and use of
wire size that can handle the current that will be passing
through it. As shown in Figure 5, leads are dressed and
color-coded so polarity is maintained; the hot side of the
AC should be switched by the SSR board while neutral is
used for return (or common). Traditionally, hot is
connected with black insulated wire and neutral with
white insulated wire as used here. Be sure that the wire
insulation is rated for household voltage.
Each channel of the SSR board is rated for two amps,
so you should limit current draw to less than that. In my
case, I was driving a single string of LED lights that draws
very little current. Depending on your current draw, make
sure your wire size is sufficient; for two amps, #18 wire
will be adequate. For the common hot and neutral wires
feeding the SSR board and lights, the current draw will be
eight times the individual channel current draw. In my
case, the total current draw is still low, but could be
significant in your configuration. If each channel is passing
close to its two amp limit, your common feeds need to be
at least #14 wire. If you don’t have experience in
determining current draw and sizing wires appropriately,
get help from someone who knows how to do this.
Connect the hot side of the outlets for your lights to
the switched side of each channel on the SSR board. The
neutral side is shared among all channels; use wire nuts to
connect the neutrals together. Don’t do this with just one
wire nut. Connect two channels together to the common
neutral with one wire nut and daisy-chain to the adjacent
channels. This not only gives a neater layout but also puts
less stress on the connections.
Plastic screws, nuts, and standoffs are used to support
December 2014 49
■ FIGURE 4. Microcontroller circuitry built
on a perf board.
■ FIGURE 3. Microcontroller board mated to the
■ FIGURE 5. Close-up view of the AC wiring.