■ FIGURE 4a. Project’s top view.
shadowing that of a nine-volt battery
— this project uses both leaded and
Surface Mount Technology (SMT)
devices, which are evident in the
photos of Figures 4a and 4b, respectively. I chose moderately-sized SMT
devices, so as not to tax your soldering
skills too much. Please note that for
ease of assembly, the SMT devices
must be soldered first.
A note on capacitors C1, C5, and
C6: These are 1 microfarad devices, and
they are available as either a ceramic or
electrolytic type. You can use either one
but the ceramics are the preferred
devices. However, if you choose an
electrolytic, pay attention to the polarity signs. C3 and C7 are (because of their
value) found almost exclusively as electrolytics, so do pay attention to polarity.
Since the circuit has so much
gain, it is important to isolate the
microphone from the circuit board. Do
not install it flush against it. Rather
leave a 0.1” to 0.2” gap, and then fill
that gap with hot melt glue for
mechanical stability. Speaking on the
subject of microphones, you may wish
to mount it remotely. If you do so,
please remember that electret microphones are polarized. The square pad
on the board is positive. Use shielded
cable for the hookup. Please note:
This project is not designed to work
with dynamic type microphones.
The board connects to the external flash with hookup wire to the
flashes’ hot-shoe via an inexpensive
adaptor (see Figure 5) or, in some
instances, the flash may have a phono
plug for external triggering (see Figure
6). You may find out that many times
the flash units or hot shoe adaptors
■ FIGURE 4b. Project’s bottom view.
PCB is not much larger than a nine-volt
have a coaxial type connector called a
PC connector, somewhat unique but
very common to the photo industry.
This connector is clearly visible in
the hot shoe adaptor photo. Prior to
attempting to trigger the flash with
this circuit, you must determine the
polarity. Do this by powering-on the
flash unit by itself, then connect the
hot shoe adaptor and identify the (+)
and (-) leads with a multimeter in the
volts range. Then connect them to the
proper PCB pads, W3 and W4, respectively. Likewise, the battery’s (+) and
(-) leads connect to W1 and W2.
Testing the Circuit
■ FIGURE 5. Flash hot-shoe adaptor.
Photo courtesy of B&H Photo and Video.
To initially ensure that the circuit is
working properly, you do not need a
flash unit or a camera.
After you have double-checked parts placement and the soldering
(especially important for
the SMT devices), connect the nine-volt battery, set the potentiometer at maximum gain,
and clap your hands in
front of the project.
You’ll see the LED flash.
■ FIGURE 6. Some
flashes provide a mini-phono side connector
for external triggering.