is convenient, allowing the wire OR-ing of the outputs of
U1A and U1B.
This circuit would be fairly easy to construct on a
breadboard. I was building more than one, so it made
sense for me to have PCBs made. I used ExpressPCB for
both the schematic and PCB layouts. Figure 2 shows the
assembled component side of the PCB, and Figure 3
shows the solder side. The resistors on my board are
installed vertically, with one lead bent over running parallel
to the body of the resistor. Anyone who has seen the
inside of an early transistor radio will recognize the
geometry. It conserves board space without the need for
Figure 4 shows the inside of the face of the enclosure.
Having all the parts mounted on the face makes it easy to
get to the batteries without stressing any wires.
There are opportunities to reduce the board size and
component count. Surface-mount components could be
used, for example. LED1 and LED2 are
conveniences and can be eliminated if desired.
LED2 is a green LED to indicate when power is
on, and LED1 is red and turns on with the beep.
Eliminating the LEDs and their associated
resistors would extend battery life in addition to
reducing component count. However, I find their
I installed banana plug jacks for the probes,
which makes it easy to swap out different types.
Sometimes I want a sharp point probe.
Sometimes I want a J-Clip or an alligator clip. For
beeping out cables, I use a probe with a header
pin soldered to the end of the wire. This allows
me to insert the pin into a connector socket and
poke around with the other probe, eliminating
the need for a third hand.
Whatever your particular use, I hope you
find this continuity tester helpful. NV
May/June 2018 39
; FIGURE 4. Inside cover of enclosure.
; FIGURE 3. My PCB, solder side.