Controlling analog strobe light

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I'm using three 75W strobe lights in my current project and would like to control them using an AVR. According to various sources on the web, analog strobes take a 10V+ pulse to trigger - connected using a 1/4" mono plug.

My idea is to use a logic level n-channel MOSFET as a low-side switch. I haven't used MOSFETs before, but the reading I've done makes me think this is a wise choice.

Any input? Possible schematic?

Thanks!

I have too many hobbies.
s-conductor.com

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The following image demonstrates a typical low side driver using both an NPN transistor and an N-Ch FET.

Note that the Fet doesn't require the Gate lead series resistor, which an NPN transistor does require.

Note shown, however, is a 10K pull down resistor on the FET's gate, to ground. This is optional, and holds the gate low during the very brief start up period when the micro is first turned on. Some circuits benefit from this, in others it isn't necessary.

HOWEVER:

I'm not sure you really want a low side driver.

If the strobe really wants a 10V pulse, (normally low, high briefly at 10V, then low again), then replace the "Load" with a 4.7 K resistor. Connect your strobe trigger signal at the junction of the resistor and the Drain. Turn the micro pin high, to turn the FET ON, to make the trigger LOW as the usual state. Then turn the micro pin low, Fet OFF, Trigger High, briefly, for the pulse.

(This is "reverse logic").

The other strobe lead is ground.

However,

Do YOU have a schematic of your strobes?

Presumable this is a low level input pulse to trigger the trigger circuitry inside the stobe, and is not the signal directly connected to the flash transformer's primary.

Presumably the 1/4" phone input is isolated from the 120 VAC ( ? ) power source for the strobes.

Note that with several output pins you can trigger each one separately, or simultaneously, for various effects. (But you already knew that).

If the above assumptions are not correct, then your trigger circuit should contain an isolated output, and protection for any high voltage transients on the lines coming from the strobe.

JC

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I am confused (as usual) ... are these strobes powered from your 120VAC or a DC supply? If the former, I don't think a Mosfet would be suitable. An SCR or Triac might be safer.

Cheers,

Ross

Ross McKenzie, Melbourne Australia

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Thanks for your input. Here is the strobe I'll be using. http://www.chauvetlighting.com/techno-strobe.html

DocJC wrote:
I'm not sure you really want a low side driver.

If the strobe really wants a 10V pulse, (normally low, high briefly at 10V, then low again), then replace the "Load" with a 4.7 K resistor. Connect your strobe trigger signal at the junction of the resistor and the Drain. Turn the micro pin high, to turn the FET ON, to make the trigger LOW as the usual state. Then turn the micro pin low, Fet OFF, Trigger High, briefly, for the pulse.

(This is "reverse logic").

The other strobe lead is ground.

After reading more about analog dj strobes, it appears some will flash repeatedly if the trigger line is held high, while others will only fire a single shot. I will definitely need to hold the line low.

Using the reverse logic idea wouldn't I also want a resistor between the drain and the trigger lead, so that when the MOSFET opens it's resistance is lower than the trigger path? Also, when a MOSFET is fully on, it doesn't need to dissipate a lot of heat, correct?

Would it be better to use a high-side driver? Does that require a p-channel?

DocJC wrote:

However,

Do YOU have a schematic of your strobes?

Presumable this is a low level input pulse to trigger the trigger circuitry inside the stobe, and is not the signal directly connected to the flash transformer's primary.

Presumably the 1/4" phone input is isolated from the 120 VAC ( ? ) power source for the strobes.

JC

From what I can tell, this is a standard for this kind of strobe. The following document lists a Remote Trigger Signal @ 10V in the first table. http://www.1111.sk/pages/doc/strobo.pdf

I have too many hobbies.
s-conductor.com

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Well, understand all of the precautions that go with working on 120 VAC equipment...

Although many of the tables list the 10 VDC pulse to trigger the strobe, I did not see any TECHNICAL Manual, with timing spec's, isolation information, etc.

One approach, IF one were to pursue such a project, would be to open up one of the strobes and see what the input circuitry consists of. The first goal here is to see if the trigger is electrically isolated from the 120 VAC and the high voltage power supply for the Xenon tube.

If one was lucky, the input would just be a resistor and an optocoupler into the remainder of the circuitry.

One could also purchase the low end, (lowest cost), controller and put its output on a scope to see the characteristics of the driving signal. Then open it up and see what kind of driver is used. Does it have to power an LED inside an optocoupler, or just provide a voltage signal, no real current draw required.

One could also try to obtain a technical / repair manual for the devices, but I doubt the company would release them.

JC

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DocJC wrote:
Well, understand all of the precautions that go with working on 120 VAC equipment...
I certainly respect 120VAC.
DocJC wrote:

One approach, IF one were to pursue such a project, would be to open up one of the strobes and see what the input circuitry consists of. The first goal here is to see if the trigger is electrically isolated from the 120 VAC and the high voltage power supply for the Xenon tube.

If one was lucky, the input would just be a resistor and an optocoupler into the remainder of the circuitry.

One could also purchase the low end, (lowest cost), controller and put its output on a scope to see the characteristics of the driving signal. Then open it up and see what kind of driver is used. Does it have to power an LED inside an optocoupler, or just provide a voltage signal, no real current draw required.


A cheap controller is already in the mail and I'm not afraid to take one of my strobes apart. :) Thanks again for your input.

I have too many hobbies.
s-conductor.com

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Out of curiosity, have you tried simply asking Chauvet? I've had to call them for parts before and their service department was quite helpful. But that said, they're a value line, and while I've not had a bad experience with their stuff, I would not hold them to particularly high standards--so it's good you're doing due diligence and taking precautions. I also hope that you bought one of Chauvet's controllers, as there's no guarantee that different manufacturers' stuff will work together in this area.

Good luck :)

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All of the parts finally arrived. The line (mono plug) to tie the strobes together was isolated from the mains power that drives the actual bulb section. The scope verified the pulse was 10V DC.

I ended up using an NPN transistor to drive a P-Channel MOSFET and it works like a charm!

Thanks again for the help and suggestions.

I have too many hobbies.
s-conductor.com