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Have I got this right?

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Offline Anaglyphic

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Re: Have I got this right?
« Reply #10 on: 24 / August / 2009, 12:15:01 »
Ah. That's totally my bad. Sorry. I think of camera triggers. You specifically said it's a flash trigger, but I automatically converted it to mean a camera trigger and kept moving. :b

The reason you're having trouble measuring it, flash triggers are switches, they momentarily short the hot shoe/PC pins together. So it's going from 0V to 0V and back to 0V. Without injecting your own voltage to measure, you'll never see your meter deflect. You might be able to catch it on Ohms setting, but it's a fraction of a second, anyway.

good news / bad news:

The good news is the circuit is about the same... we don't need an inverter so you'll move the output connection from the collector side to the emitter side, and we need the USB to stay at +V (somewhere between 3 and 5V, 6 tops!) until the trigger fires, so you'll move the other end of the base resistor to +V to act as a pullup. You can eliminate the collector resistor.

The bad... it's not going to be that simple. Working in darkness and leaving the shutter open and firing the shortest burst you can, the timing part only involves two syncronizations - the object in motion and the flash burst. Controlling the camera instead, you'll add a 3rd time-sensitive calculation.

Another bad, CHDK can fire on the rising edge of USB voltage, but it's much less accurate timing-wise than the falling edge. The camera doesn't function with voltage on USB unless there's a break. (by default SDM & CHDK in sync mode uses two breaks, one to focus/setup and the 2nd to fire.) But, since your trigger has no idea about what it's triggering, you'll need to wire up a momentary pushbutton where you can do the short-to-ground first "half press" and then the flash trigger will fire the shutter. I could see where after forgetting a few times and the camera not firing, this would become "bothersome". (no cussing here.)

Finally - what's that truism about "bad news comes in 3s"? - there is a delay between detecting the USB voltage drop and firing the camera. It's much more repeatable than the rising edge, but it is still a delay, and it is still (slightly) variable. For most PowerShot models, about 1ms variance, which isn't a lot... except in doing 1/20,000+ flash bursts... then it's huge! So your firing delay will have to be adjusted for by making the flash trigger fire that much faster. (we'll say 50ms, it's per-camera, so it will take some experimenting.) This last one isn't really new bad news, more like an error of omission. It would still be an issue when I thought your flash trigger was a camera trigger.

Oh, and one more bit of good news: I had never heard of this Quaketronics flash controller, but it seems it's an Open Source project, and the current revision is running off a PIC16F616, so there's probably a very easy way to do this in software if you have this model. I've looked at the schematic and the output control for both CONN1 (the hacked-up disposable) & CONN3 (the strobe) come from the same pin off the microcontroller. But there is hope! There's a spare output pin (RA5) that could be appropriated for CHDK USB triggering. I would ask on his forum, or on the MAKE: forum, or just email him personally and point him over here. But someone else may have already done this exact modification... anyone into DIY photography will end up finding CHDK.

Happy hunting! :D
Since we cannot know all that there is to be known about anything,
 we ought to know a little about everything.
-- Blaise Pascal

Re: Have I got this right?
« Reply #11 on: 26 / August / 2009, 01:40:51 »
Hello - Tom from Quaketronics here. I just learned about CHDK and it looks like fun!

I don't know how to use the Quaketronics controller to get good results with the USB. The 1/4" connection sends a 4.3V pulse for about 1/1000th of a second. I don't know if this would be suitable for the USB trigger or not.

I have tried using the cable release input on my Nikon D70s and it has too much random time delay to be useful for high-speed photography. I think you should be able to get rid of some of this delay using the CHDK, since on my Nikon I had to wait for both the mirror to swing out of the way as well as the random firmware delay. Both of these delays were plenty large enough to ruin the potential for high-speed synchronization on my Nikon. I used a relay circuit to drive the Nikon cable release.

Here is a wild idea for how to overcome the timing problem: Can you get the camera to make a sound when the shutter opens? If so, you could trigger a strobe with the Quaketronics flash controller by having it monitor this sound. The sound of the mirror swinging out of the way is very loud on my Nikon, and can easily trigger the flash controller. I think that you can lock the mirror on your Canon (unlike my Nikon) and then maybe the shutter will make enough noise, or maybe you could use CHDK to add some sort of beeper function. Triggering off the mirror noise would probably have too much timing uncertainty.

To build a high-speed rig with this idea, you would need two Quaketronics controllers (aw, shucks). One to send a signal to the USB to trigger the shutter, and then a second to listen for the sound of the shutter to trigger the strobe. Getting enough audio isolation between the high-speed event and sensing the sound of the shutter might be impractical, though, especially if the shutter doesn't make much noise. It might be great for photographing water drops, though, since they don't make much noise. The best case would be if you could get the camera to beep just before the shutter opens, and if you had a headphone output that could drive the flash controller.

You are welcome to reprogram the Quaketronics controller. The processor is socketed in case you want to set aside the original chip. The controller board has a programming connector that is compatible with the ICD-2 PIC programmer. The source code and schematics are on our web site at www.quaketronics.com . The flash controller's printed circuit board construction is all hacker-friendly through-hole. There is a hole in the board next to each pin on the processor to make it easy to solder on extra wires.

If you are new to electronics, I recommend finding a friend with an oscilloscope before starting this project! Debugging high-speed electronics is very difficult without this tool - it is the best way to see what is going on. A voltmeter is not sufficient for high-speed work.

Also, the ICD-2 PIC programmer is not free. We had to use the PIC because it was the only chip that we could find that had the exact combination of features that we needed. There are less expensive, easier to learn alternatives such as the Arduino that might work better for your project.

Please feel free to contact me at Quaketronics if you have any questions. I read all the mail that comes to the support address listed on the web site.




Offline CMC68

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Re: Have I got this right?
« Reply #12 on: 26 / August / 2009, 02:21:43 »

Thanks so much for responding to my email and coming over here to reply.

The electronics side of your reply is beyond my level of understanding but hopefully Anaglyphic or someone else can comment on this side.

A couple of things I noted from your reply though.

Firstly, CHDK is for point and shoot Canon's only, mirror issues and their sound are not relevant in this situation.

As for using two controllers I'm not sure this is totally necessary either. CHDK allows very high shutter speeds to be set (reported between 1/10000 and 1/40000 ish) but also with flash synced. An external flash is therefore not needed. The only exception would be if more light than is available from the on board flash is needed. But my thinking suggests that full power could be set as the flash duration can be as long as we want in this situation as it is the shutter duration that freezes the motion.

What I'd be interested to know from one of the CHDK/electronics experts is:

Should 4.3v for 1/1000th sec be enough to trigger over USB? if so its broadly simple but how best could the 'half press' trigger/button be incorporated?
Can CHDK settings select a fast shutter speed AND slow (in turn high power) flash duration?

If that works were sorted. Just the delay between the USB and firing to be dealt with.

If it doesn't, then its a programming job by the sound of it. Way over my head.

Thanks again.


« Last Edit: 26 / August / 2009, 07:07:12 by CMC68 »


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