Paul C. Buff, Inc. Technical Forum

Hello,

I have an application where I have to trigger my Zeus Z2500 power pack using a voltage signal from a function generator (rather than the PC port on a camera).

The website specification lists "less than 6 volts (safe for use with digital cameras)" under the "Sync / Trigger Voltage" category for the Z2500 power pack. However, when I send in a voltage pulse at around 5.75 V, the flash head is not triggered.

Has anyone else tried to do what I'm trying? If so, have you had any success?

Thank you.

Are you just applying 5.75V to the circuit? You will need to have it so that the waveform that triggers the light falls below 0V, and the light will fire on the falling edge of the wave form.

I am sending a pulse from 0 V to 5.75 V and back down to 0 V in an attempt to trigger the flash. I will try your suggestion of having the waveform fall below 0 V.

Thank you.

I just used a pulse that went from -0.5 V to 5.75 V and back down to -0.5 V and the flash did not go off. How far negative does the pulse have to be?

Thanks.

You're doing it backwards. The Zeus outputs about +5V to the camera at its sync input. To fire it, the camera shorts this +5V to zero momentarily, discharging a small capacitor in the Zeus through about a 200 ohm resistor and internal optoisolator.

A function generator would have to be at +5V, then drop to zero momentarily to fire.

But I doubt most function generators have low enough output impedance to discharge the the Zeus internal capacitor.

You may have to add a transistor or small Triac to the generator output to simulate a relay that closes when you want it to fire.

You don't need to supply voltage to the Zeus - it supplies the approximately +5VDC - you need to short that supplied voltage to fire.

Thanks a lot for your detailed explanation Luap.

Since the Zeus is constantly outputting about +5 V and this needs to be shorted to zero momentarily to fire, do I need a function generator at all? Can't I just trigger the flash using some circuitry to drop the +5 V down to 0 momentarily?

My mistake - I misunderstood what you were saying. So when the Zeus is actually connected to a camera, it outputs +5V. However, since I am not connected to a camera, I have to simulate this situation.

Could I build my own circuit using the +5V output from the function generator and drop this +5V over my own 200 Ohm resistor? I would just use a simple switch to momentarily drop the voltage down to 0. Would this eliminate the problem of the function generator having an output impedance that is too high?

Thank you.

You don't need a function generator or 200 ohm resistor or 5V supply. You just need a switch that shorts the Zeus sync terminals momentarily . . . physical switch, triac, relay, etc.

I connected the Sync port to an oscilloscope, and all I saw on the scope was a constant 0V (nothing changed even when I manually hit the TEST button). Does the Zeus Power Pack only supply the 5V when it is connected to a camera using the camera's PC port?

Thank you very much for your help.

You should have seen around +5V across the sync terminals - not from one sync terminal to ground. This voltage is always present at the sync jack, and test button has no effect on it This is a high impedance circuit, so even a scope impedance of 1M may drop the 5V to a couple of volts.

To test this, just plug in a sync cord and short the sync terminals with a paper clip or wire - it should fire the Zeus . . . that's what the camera does.