Flash Slave Trigger

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Flash slaves are used when you need to supplement one
flash unit with one or several more. This slave trigger simply triggers
those other units. It does this by "seeing" the first flash (using a
phototransistor) and triggering the other flashes a few microseconds
later. The sensitivity of the circuit is adjustable to compensate for
ambient light or dimmer than usual master flashes.

Schematic

Parts

Part

Total Qty.

Description

Substitutions

R1

1

47K Linear Pot

R2, R3

2

3K 1/4W Resistor

R4

1

220 Ohm 1/4W Resistor

R5

1

680 Ohm 1/4W Resistor

C1

1

10uf 25V Electrolytic Capacitor

C2

1

0.047uf 25V Ceramic Capacitor

Q1

1

2N5777 NPN Darlington Phototransistor

Q2, Q3

2

2N3904 NPN Transistor

2N2222

SCR1

1

400V 2A SCR

S1

1

1A 120V SPST Switch

P1

1

Plug to match jack on slave flash

MISC

1

Knob For R1, Wire, Board

Notes

Q1 should be aimed at the master flash. R1 should be adjusted for maximum
sensitivity but no false triggering.

Keep your fingers away from SCR1 when the circuit is operating. It is at
50V-300V and will give you a nasty shock.

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Comments

anonymous

Flash Slave Trigger

Tuesday, September 11, 2007 12:26:35 PM

R5 - 680 ohm will do just fine with a (SCR1)
TIC 106 a good sensitive contruction, ;) but only the first flash trigger
this circuit. most camaras give two, or use manual mode on the camara.
then you have to think again, but the digital cam give a preview. this way
you can make a other picture. .

Ameya

Flash Slave Trigger

Saturday, July 07, 2007 9:38:10 AM

How much power supply I shoud give it?

anonymous

Flash Slave Trigger

Thursday, July 05, 2007 5:33:21 PM

R5 please...you owe us that much

(Editor's notes: Search the forum.)

WildSwan

Flash Slave Trigger

Tuesday, July 03, 2007 2:33:59 AM

Is it possible to use the trigger voltage of
the flash unit to power the trigger instead of using a separate 9V cell?
If so, how do we go about this?

miguel_pork

Flash Slave Trigger

Sunday, April 15, 2007 1:11:45 PM

tip: dont construct a circuit before
verifying all parts.;)

Yehya

Flash Slave Trigger

Tuesday, April 10, 2007 7:51:42 PM

What's the value of R5?

(Editor's notes: Search the forum (or for just read prior
comments).)

delfuego

Flash Slave Trigger

Monday, April 09, 2007 5:52:11 PM

The exact value of R5 depends on the SCR
being used. Try 4K7 (that's 4.7K in old money) as a starting point. If
your SCR doesn't fire then reduce until it does reliably.

Sinister Dragon

Flash Slave Trigger

Saturday, March 31, 2007 4:06:40 AM

Thanks, been looking for something like this
online for ages. NOw I can cheaply and easily make a slave trigger for my
"disposable" flashs.....

anonymous

Flash Slave Trigger

Friday, March 23, 2007 9:31:09 AM

yeah i also see that the Resistor 5 has no
assigned value therefore we cannot complete that project or circuit
whatever you called that.. pls tell us the value of R5.. Thnx

(Editor's notes: Search the forum.)

Charles

Flash Slave Trigger

Thursday, March 15, 2007 12:11:48 PM

Um yah - Was halfway through construction
when I realised no value was supplied for R5.

(Editor's notes: Search the forum.)

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