The standard SK2-DU circuit like the other HiViz.com trigger circuits uses SCR output stages. These act as switches and also protect the circuit from the high voltages across some flash units. In cases where the flash unit is low voltage--this applies to most modern units--an optocoupler may be used as a replacement for an SCR. The advantage of an optocoupler is that it provides complete electrical isolation between the trigger circuit and the flash unit. Such isolation is more important if you're triggering a camera rather than a flash unit. The instructions below show how to replace the delay unit SCRs with optocouplers. If you need to purchase optocouplers, see this page for the PS2501 optocoupler.
Click on the photos below for larger versions that will open in new tabs or windows.
The SK2-DU circuit with SCR outputs is shown below.
Begin by removing the following wires and components. See the photo below for the breadboard after removal of the wires and components.
the SCR in holes 11-13B
the SCR in holes 15-17B
the 100-ohm resistor from 12D to 20D
the 100-ohm resistor from 16C to 23C
the wire from 9E to 18F
the wire from 11A to ground
the wire from 15A to ground
Now insert the following wires and components:
Seat the PS2501 optocouplers as shown in the photo below. Note the location of the dot on the face of each optocoupler. The leg nearest the dot on the left optocoupler goes in 10E, and the leg nearest the dot on the right optocoupler goes in 12E.
Insert the two 100-ohm resistors from 11B to ground and from 13B to ground.
Connect wires (these are the yellow wires in the photo) from 20D to 10D and from 23C to 12C.
Connect a wire (this is the blue wire in the photo) from 9C to 18F.
For the delayed output (shown in the photo), insert your flash trigger cord into holes 12H (+) and 13H (-). For the immediate output (not shown), insert your flash trigger cord into holes 10H (+) and 11H (-).
If you're connecting a camera, use the same holes as in step e. Connect the common (ground) wire of the shutter cable to either 11H or 13H and the shutter wire to either 10H or 12H. If the focus wire of the shutter cable has to be grounded before the shutter can actuate (for Nikon cameras, for example), connect the focus wire to either 11G or 13G depending on which output you're using.