Sequential flashes

Initial requirements discussion

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Sequential flashes

Postby feralfoto » Mon Sep 24, 2007 11:50 am

I have 3 ebay wireless remotes with 16 channels. What I would like to see is the transmitter send a command to fire channel 0 on the first actuation, channel 1 on second etc.

Then I would be able to get (in my case) three off-camera flashes at full power using the motor drive function on my camera when trying to get better sports photos.

With 16 chanels, imagine 16 Vivitar 283s at half power with lead acid batteries for fastest recharging (less than 2 seconds) , and with a Nikon D2X at 8 fps taking photos of BMX riders against the sky, basket ball players going for a goal, gymnasts etc. Fun++
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Very interesting

Postby Thonord » Mon Sep 24, 2007 3:07 pm

If we use a good wireless chip
If we program the microcontroller
If we write the protocol

I don't see why not!
All it will require is a wee bit extra code.

Tom
Ppl who agree need normally not reply, those who disagree or have questions do.
Or - just ignore me.
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Postby feralfoto » Wed Sep 26, 2007 10:22 pm

Upon reflection, this might be easy.

My trigger is http://cgi.ebay.com.au/Digital-Radio-Sl ... otohosting

My wireless transmitter has 16 radio chanels, normally selected by a 4 pole DIP switch channel selector and it has an open flash switch as well.

1. put a ACSL-6400-00TE 4-way optocoupler in parallel with the DIP switch.
2. put another single optocoupler in parallel with the pushbutton open flash switch.

Control these 5 optocouplers with a picaxe, with
- input from the camera hot shoe trigger
- 4 outputs to the ACSL-6400-00TE
- 1 output to the single optocoupler

As the hot shoe fires in sync with the continuous shutter, I fire the open flash and cycle through the channels. Representing the state of the 5 optos as F-xxxx (F is the open flash trigger and xxxx is the state of the ACSL-6400-00TE), I repond to 4 exposures like this
1-0000
1-0001
1-0010
1-0011
I have just fired four flashes in sync with 4 frames of a 'motor drive' and sent the radio signal to channels 0, 1, 2 then 3.

Just what I want for gymnastics at a distance.

A refinement would be to have a input DIP switch to control the number of channels to cycle through. :-)

I think it would work, just need to read the doco on the opto-couplers to decide which to use.

Cheers
the Feral Photographer
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Postby brittonphotography » Wed Sep 26, 2007 11:56 pm

i had the same thought!

if you had 10 flashes you could even match the 10fps of the 1DMARKIII
Otherwise the 10fps is worthless if you are shooting with flash.

good idea, i would like to see this as well!
i think it could be a great selling point to be the only wireless trigger to have such a high fps matching capability (with multiple flash units)
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Postby feralfoto » Sun Sep 30, 2007 2:13 am

brittonphotography and feralphoto are working together on a proof of concept for this feature

Mr Strobist, thank for the intro.
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Other method (much simpler)

Postby Rudeofus » Sun Sep 30, 2007 5:31 pm

Wouldn't it be much easier to intercept the trigger output of the remote receiver and distribute it to any number of flashes in a round robin fashion ?
The trigger output is usually just an open collector/drain output, which you can easily feed into a micro controller input (with external or internal pullup resistor).
All your micro controller would have to do is wait for a trigger pulse (=falling edge) and forward the trigger pulse to the next flash in the row.

Advantages:
- no messing with the cactus triggers required, just feed its trigger output into your circuit
- supports as many triggers as you have output pins on your micro controller
- only one cactus receiver needed
- The micro controller can automatically detect flashes connected to it -> no configuration required
- You occupy just one channel, i.e. are more friendly to other photographers at the event

Disadvantages:
- the flashes need to be close to each other (unless you want to run long cables between them), but I guess that was your intention if you want to rapid fire without changing light conditions
- much easier to do -> less hack value :wink:
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Re: Other method (much simpler)

Postby JonSenior » Sun Sep 30, 2007 7:34 pm

Rudeofus wrote:Wouldn't it be much easier to intercept the trigger output of the remote receiver and distribute it to any number of flashes in a round robin fashion ?


Even easier. There are discrete ICs that will do this. From memory a counter (1 input / BCD outputs) and a BCD -> Decimal decoder will do this for as many outputs as you choose to engineer. All TTL / CMOS logic as you prefer. Selecting which of the decimal outputs to wire to the RST line of the counter will allow control over the number of strobes. A micro would be allow more sophisticated control, but I could probably knock up a circuit using traditional discretes in an hour or so.

Jon
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Postby feralfoto » Mon Oct 01, 2007 9:55 am

Thanks for the tips about counters. I have one under construction on my prototype board and it seems like a good solution.

More results in a week or so

Cheers
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Many flashes is good

Postby Thonord » Tue Oct 02, 2007 6:09 pm

The protocol I presented in a draft proposal mode would allow this.
Its based upon the master initiating a "Role Call" so it knows how many flashes there are.

It is then easy to implement a "sequence system" where the master says: "Fire 1,2,3,4,1,2,3,4 Or what ever.
Tom

Unfortunately I see serious probs with us doing anything related to firing flashes with RF.
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Re: Sequential flashes

Postby jkingdon » Tue Aug 19, 2008 3:54 pm

So, if what we are trying to do is achieve high light output at high frame rate, what is the benefit over firing individual flashes in sequence compared to firing all the flashes at reduced output? For example, if we have four flashes I can choose to sequentially fire each at full power, or I could fire all of them at 1/4 power. Either way I get the same amount of light and (I think) the same max rate. Firing all of them at 1/4 power has some advantages - larger effective light source, and greater frame to frame consistency. I was thinking of implementing all sorts of complicated sequencing options until it occurred to me that I couldn't see any benefit. Except for the one really special case where you actually want a sequence of frames with completely different lighting angles...

James.
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