I wanted a slave flash for my CoolPix 995. I looked all
over town for one and couldn't find one so I resorted to calling and old
friend make Veldman WD0CTA who can come up with solution to almost any electrical
problem. He speculated that if we use an audio transformer and a photocell
to trigger a SCR we could filter out the constant light and only trigger
on the flash and not need a battery. He fixed me up with a transformer and
photo cell but he didn't have an SCR (Silicon Controlled Rectifier) were
he was so I went by Radio Shack to get one. Unfortunately they were our but
they did have a 6 amp Triac part number 276 1000 which is 2 SCR diode back
to back. It has some other differences but I though I could probably make
I was having trouble getting the transformer to work because low impedance
winding was swamping out the voltage. I could have built a resistor and capacitor
network to over come the problem but first I decide to just hook up everything
direct to see if it would work.
I tied the positive voltage line from the trigger and the negative photocell
wire and the negative wire from the flash trigger to the pin opposite from
the trigger and tied the positive wire from the flash trigger to the center
pin. It works like a charm in doors.
Reviewing this it should have a 1,000 to 2,000 OEM resistor in series
with the gate or trigger of the Triac to limit the current to 20 ma and it
should have bypass capacitors across both terminals to ground of 0.1 mfd
I am sure it won't work out doors but for use with a microscope it is just
what I need and the batteries never run down. If your solar cell put out
more than 20 ma you should put a current limiting resistor in line to limit
it to that amount. The SCR is rated to 400 volts and my flash has 150 volts
at very low amperage on the control terminal. The amperage is so low that
100 Ohm resistor won't trigger it.
If you have a problem with too much light just put metal tape over part of
the cell to block part of the light out. It triggers from ten feet away and
it trigger if I point it right at a light so I expect I need some tape.
It's not an all around answer but for a microscope or macro setup where you
are in control the light you can't find a much cheaper solution than $4.99
for Radio Shacks 276 - 124
and $1.49 for their 276-100 Triac
While the voltage on the controls of the electronic flash are very low amperage
they are still high enough to be fatal if you should pierce your skin with
the wire and have a really unlucky day. Much more likely they can make you
hurt yourself if you accidentally touch them when they are charged. Before
solder directly to them turn off the flash and discharge it several time
and short the wires together for sometime before working on them. Better
get a connector and don't work with the wires at all.
reserved Gordon Couger
September 25, 2002 References
by hyper link welcome.