board (a.k.a., perf board). Figure 6 shows an overhead
view of the assembled perf board circuit and highlights
the main components. Even though the MOSFET I used
doesn’t dissipate the bulk of the power (the light bulbs
do), I did equip it with a small heatsink as it can get
slightly hot when drawing high currents (in excess of 3A).
Figure 7 shows the underside of the board. Pay close
attention to the portions of the circuit where the
potentially high load current flows (this is the portion of
the circuit represented in the bottom of Figure 3).
Make sure the wire gauge is thick enough to handle
the current through these paths. It also helps to re-enforce (with solder) the high current flow paths as this
lowers overall electrical resistance. Also try to keep
these connections as short as possible.
Figure 8 shows an early prototype as it was before I
committed the circuit to a proper enclosure. Here, you
can see the multi-turns potentiometer and the three lamps
connected to the main board.
Figure 9 shows the circuit inside a small plastic
enclosure. Notice the 9V battery mounted on the bottom
left portion of the box.
Figure 10 shows the final product front panel and
highlights the main controls and indicators.
July 2016 45
■ FIGURE 7. Back of the board.
■ FIGURE 8. An early prototype.
■ FIGURE 9.
■ FIGURE 10. Front panel with controls and