Help with flash slave trigger project

[mhatay]

Project overview.
I am helping a student build a system to be used in a marine biology experiment.
She is looking at the oxygen released by coral. This measurement combined with other factors can be used to calculate metabolic function.
We intend to use a material called “Optodes” It is a chemical film that is applied to a sub-straight, in our case Mylar. This Mylar strip is put in close proximity to the coral.
When this optode material is exposed to a specific wavelength of light it fluoresces. The amount of signal in a specific wavelength indicates oxygen levels.

We will be using a Canon G11 to record the signal. We are running a hack on the camera (CHDK) that allows us to control all functions of the camera run scripts and record in RAW.
We use (rawhide) to separate the RGB channels and write the values to an Excel file.
To excite the Optodes we use Royal Blue Tri-Star Rebel Led’s.

We have successfully been able to do this on the bench.

So far we have been working on the bench. We turn on the bank of Led’s take a picture and turn off the Led’s
In the field we will need to take a time series over 24 hours. The CHDK hack allows us to run a time laps script, so the camera will fire at a predetermined interval. For sake of discussion every hour.

The task of turning on the LED bank still remains. A Led flash would be a sophisticated solution but I am reluctant to try to build a synchronized device on relative short deadline.
Another solution is to just turn the bank of Led’s on take the picture and turn it off again.

What I would like to build is something like a slave flash trigger, but add a time delay to keep the Led’s on for a few seconds.

We need a circuit that switches on, triggered by a optical pulse (flash) or the sync out from the camera.
Runs a timer between 0 and 6 seconds and turn off again.

There are a few ways this Led switch could be used.

1, Program the camera to take 2 pictures for every data point ~ 1hour intervals. The flash is set to on.
A photo detector sees the flash and turns the Led bank on, runs a timer and turns off. The time is set to overlap the second exposure.
The first flash would be just a wakeup for the Led bank, the second image would be the data.

2, Some underwater camera cases have a connector for flash sync.
In this case connect the sync to the circuit and program camera as above, to take two pictures.

3, We might be able to program the focus assist light to go on before the picture is taken.
In this case it would turn on the led bank and only one picture would be needed.

Since battery consumption is critical option 2 or 3 would be preferable.

I need to know what the power consumption will be, I can fit seven NIMH - D cells in the case.
That would give me 12000mah @ 10.5 volt


I have the underwater housing issue under control, two Sea and Sea Model 300 casings.


LED bank.

9 X 875mw royal blue Led’s ( 3 X 20mm tri-stars )
https://www.luxeonstar.com/Royal-Blue-447-5-nm-20mm-Tri-Star-Rebel-p/mr-r0500-20t.htm.
They would be wired three in series, three in parallel.
I think I can use the power module A900-D-V-2100 BuckBlock
**broken link removed**

Thanks for any help,

If you are in the San Diego area give me a call, 619 990 1299
Mark
SDSU

 

[squishy36]

Hi, Mark -- welcome... I am unclear why you use the camera. Why not just use a simple sensor -- say, a photodiode through a suitably-colored filter to measure the fluorescence? I would also think that this could be packaged in a pretty small package, which might be convenient (and need only one LED to cause fluorescence). I'll assume a typical measurement would be to measure with the LED off, then on and record the difference to get rid of the effect of ambient light.

If I was doing the project, I'd probably use a microcontroller to control everything. An advantage is that the firmware could be tuned to get things to work the way you want and it could be made low power to boot.

If you're at a university, I'd suggest you first write down the project's goals and the constraints you operate under. Then call a blue sky or design review meeting with various folks from other departments, especially electrical engineering and physics. The blue sky meeting's purpose would be to harvest ideas on how best to make the desired measurements; the design review's purpose would be to present the rationales used to select the design and get feedback on the approaches used.

The reason I think this would be important is there are other methods of measuring oxygen concentration. It wouldn't hurt to look at the other methods and have a discussion about which is best. It would also be a good learning experience for the student -- how to leverage the knowledge of other folks (and leading such a meeting and keeping it focused on the task at hand). And the one thing I've learned from 40+ years of doing such things is that the clever folks you invite will always think of interesting things you didn't think of before.

 

[mhatay]

Greetings Squishy39,

The reason of using a camera is we are recording a two dimensional array. Our target is 30cm X 20cm
The Mylar is cut to fit the contour of the coral. The oxygen coming off the coral is picked up by the currents.
The optode array measures not only how much oxygen is being produced but also how it is being distributed.
The actual experiment is a lot more complex and specifically address some biological questions pertaining to coral disease.
Yes there are other methods of measuring oxygen, none that can measure arrays with minimal environmental impact.
We are not the first to use this technique, just the first to use it underwater.

My rather lengthy explanation was to give a little insight to what I want the circuit for.
You are right on all points mentioned, and the experiment did go through a design review process.

One point to consider,
Our university has had so many budget cuts that there almost no technical support left.
When I started working here, 30 years ago there was 7 electronics technicians, today there are none.
Everyone here is overworked, overwhelmed, nobody time to help.
People might think that universities are a rich and rewarding place to work,
Frankly, what's happening is sad!

Mark

 

[ronv]

The buck puck has a minimum dropout of 10 volts. NIMH drop to 1.2 volts very quickly so you will only have 8.4 volts. This will push you to 3 in parallel and 2 in series. When this happens it makes current control iffy without something to balance the strings. Any chance you can squeeze 9 batteries into the bag?
I'm guessing the camera outputs a ground to the flash. Can you confirm this?

 

[mhatay]

You’re right, will need stay above the 10 v min for the buck puck, I will need to mock it up with some “d” cells and duck tape, see how many I can fit in the case.
I might switch to “C” cells.
Regarding the sync, camera output. The large center pin on the shoe is the sync, it is a momentary contact to ground. The metal part of the shoe is ground. There is a small switch in the left rail of the shoe that switches the flash from internal to external.
Thanks
M