it in place. Finally, measure the resistance from the tip of the
1/8” phone plug to one of the electrode clamps and mark
it with a “+” sign.
Measure the resistance from the ring contact of the
phone plug to another of the electrode clamps and mark it
with a “-” sign. The last clamp should be labeled with a “C”
for common. Make sure that there are no shorts between
the different clamps. The final assembly should look like
Use another copy of the label and laminate it for the
ECG unit. After cutting out the label, laminate it with
Fellows self-adhesive laminating sheets, leaving about a
1/4” border around the edge. It works best if you leave
about a 1/2” border around the edge of the label.
After you burnishthe laminating sheet to the label, cut
the holes out for the trim pot adjustment, switch actuator,
When all the holes are cut out and you have dry-fitted the label to the unit, make sure that all the
holes line up properly. Remove the laminate sheet
backing, and carefully align and mount the label to
the enclosure (Figure 8). It may help to hold the
aluminum up or back light the enclosure as you
lower the label and align the holes with the
enclosure. Burnish the label edges to insure the
label seals well.
The PCB is mounted to the enclosure using four
4-40 x 5/8” (preferred) or 3/4” (easier to find)
machine screws, four 4-40 by 1/4” nylon threaded
spacers, and four 4-40 nuts. Place the machine
screws through the label, screw on the threaded
spacers, and tighten. Mount the PCB on the
machine screws and secure with four 4-40 nuts
Solder the red lead of the AAA battery pack to
the V+ pad or the double soldered pins of the slide
switch, and solder the black battery pack lead to
the V- pad (Figure 9). At final assembly, a block of
foam rubber packing can be used to prevent the
battery pack from moving.
Finish the electrical assembly (Figure 10) by
28 February 2017
■ FIGURE 9. PCB installed.
■ FIGURE 10. Final assembly connections.
■ FIGURE 7. Finished cable assembly.
■ FIGURE 8. Laminated label applied to enclosure.