Camera flash sync and Led

Thread Starter

Jeremy Talus

Joined Mar 21, 2018
10
Hi everyone,

I'm trying to make a Flash (strobe) using led for my camera, it's a Kiev 60, a fully mechanical camera, and it's have an flash sync port, which is basicly a switch controlled by the mechanics of the camera :), I have tried to wired it in serie with my small LED panel and a CR123 LiIon cell.
I only get a very weak light, but if I wire the panel directly on the cell I'm getting the full brightness ?

do you think that the mechanical switch drop my current caused by high impedance ?

I was thinking of doing that :

but using 3.7v instead of 6V what do you think ?
 

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Thread Starter

Jeremy Talus

Joined Mar 21, 2018
10
Ok
so the MOSFET is not the solution.

I have 20 LEDs in parallel, I need to switch something like 400mA a BC547 can do the job ?
 

ericgibbs

Joined Jan 29, 2010
8,848
hi,
I would not recommend a BC547.
Use a medium power transistor,capable of say 1Amp.
Which transistors do you have available.?
E
 

Thread Starter

Jeremy Talus

Joined Mar 21, 2018
10
hi,
I would not recommend a BC547.
Use a medium power transistor,capable of say 1Amp.
Which transistors do you have available.?
E
I'm at work, I don't know what I have in my stock, I must have some 2n2222 (rated for 800mA that can be good ?)
I made a mistake, I thought it was rated for 1000mA, but it's 100mA :)
 

Thread Starter

Jeremy Talus

Joined Mar 21, 2018
10
hum ....
Let's say it's a Soviet Camera built in the 80's, so maybe some few amps :), and I haven't disassembly the camera to check the switch contact, there is maybe some few oxidation on it
 
hum ....
Let's say it's a Soviet Camera built in the 80's, so maybe some few amps :), and I haven't disassembly the camera to check the switch contact, there is maybe some few oxidation on it
I'm may be missing some things here, but as I understand....

The PC synch connector (hot shoe or otherwise) has +/- connections. The + will have a positive voltage from the camera battery. The flash mechanism within the camera will short the two connectors (+/-).

A very easy way of using that connector is to attach the leads to the LED side of an optoisolator with a resistor to limit the current to a few milliamps. The NPN side of the optoisolator (you could use other opto chips) could then be used to drive a higher current transistor to switch the LED flash unit. So simple, even I could do it (probably) :)

http://www.butkus.org/chinon/russian/kiev-60_dir/kiev-60-splash.htm
 
Just fire the leds directly using the Hot Shoe switch, otherwise use a Darlington transistor like a Tip142.
I do not think that the hot shoe could switch "a few amps" or even 400 mA. Not saying that an opto *has* to be used, but it makes it easier in my mind...keeps all the power switching on the LED side that has its own PS.

80s circuitry yes, but the switching back then would be one that used circuitry to drive a xenon tube of some sort as the flash - high voltage at some point but not high current. That's my thinking anyways, but why guess, optos are cheap and easy.
 

Thread Starter

Jeremy Talus

Joined Mar 21, 2018
10
My camera is fully mechanichal, there is no batery inside, (its a Kiev 60)
only a PC sync, and a cold shoe arm

hi,
If its capable of switching say 1amp, you could consider switching the LED's directly.??
E
Yes I tried, but the LEDs was not very bright, like if there is not much current to drive the LEDs

And with direct drive on the battery, work very well :)
 

ericgibbs

Joined Jan 29, 2010
8,848
hi J,
Do have an Ohm meter.?
If so measure the resistance between the shoe switch contacts, there maybe an internal series resistor.??
E
 

Alec_t

Joined Sep 17, 2013
10,429
If the switch makes only a momentary connection (which would have been all that was originally necessary for triggering a flashbulb or strobe) then the LEDs may well not appear very bright.
 

Thread Starter

Jeremy Talus

Joined Mar 21, 2018
10
I can't measure it's a pulse

If the switch makes only a momentary connection (which would have been all that was originally necessary for triggering a flashbulb or strobe) then the LEDs may well not appear very bright.
so How can I do ? Monostable circuit with very short duration ?
 

AnalogKid

Joined Aug 1, 2013
8,135
The switch in the camera is designed to control the gate of an SCR, not a circuit with any real power. My guess is that the reason the LED seems dim is that it is on for a very brief time, possibly only a few milliseconds. While an SCR has a higher Vf when on and so is less efficient, it is a natural pulse-stretcher. Consider doing what the photo-flash people do, have a large storage capacitor and an SCR switch to dump that charge into the LED bank.

Alternatively, there is nothing inherently wrong with using a power MOSFET, but you need the right kind. Search for a logic level power MOSFET to see what is available to you. A MOSFET is the most efficient switch device, once you get the correct gate drive.

Where are you located?

ak
 
Hi,
In that case you need to stretch the pulse period, using a simple circuit.
E
I think that adding a pulse stretching circuitry would be a self-defeating move and disastrous from a photography point of view. The pulse at the PC synch connector is not arbitrary it is an important part of the camera. The unit does require a 4.5V battery for exposure time meter which is I think is essential.

Having some experience using a PC synch connector and using logic level signals to operate slave flashes, I would suggest that the TS do the following.

Install a battery and look at the voltage at the PC synch connector - it should be at about 4-5V. If it is so old that there is no voltage even when you have the battery inserted in the camera, then you are going to need additional [information].

If you have an oscilloscope you should be able to see the pulse.

If you absolutely do not see any potential between the PC Synch contacts and a pulse, then you will need to provide the +/- sieds, but I would go no further until you install a battery into the camera. Also, at this point (no voltage on the contacts) I would do some serious searching on line before jumping in.

If you do see a potential between the +/- on the PC Synch connector and a pulse then:

Use that pulse to operate the LED on an optoisolator with a current limiting resistor. Do NOT simply connect the PC synch +/- leads to an LED.

Use the output of the opto to drive a higher current transistor that switches the LED strobe.

There are many modern day LED strobes for photography and I understand that many of hen work fine. Do not, however, expect great results if you are using a simple LED strip or panel that is not designed for photography.
 
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ericgibbs

Joined Jan 29, 2010
8,848
I think that adding a pulse stretching circuitry would be a self-defeating move and disastrous from a photography point of view. The pulse at the PC synch connector is not arbitrary it is an important part of the camera. The unit does require a 4.5V battery for exposure time meter which is I think is essential.
hi Raymond,
I sure you will appreciate the stretch could be as short as required, even shorter than the closure period of the actual switch [ which would not applicable in this application].
Stretching does not mean delaying the start of the flash.
E
 
hi Raymond,
I sure you will appreciate the stretch could be as short as required, even shorter than the closure period of the actual switch [ which would not applicable in this application].
Stretching does not mean delaying the start of the flash.
E
Yes, I can appreciate what you are saying and also, I do not want to suggest that the duration of the PC Synch signal is dynamically altered by the camera for different exposures. "Disastrous" was too strong and "probably unnecessary" would have been better.

I think that the OP needs to do a little homework on this before we all jump in with circuits. That is why I linked to the manual for the camera (assuming that is the correct model).

Once a battery is placed in the camera and a determination is made about a voltage at the PC Synch connectors, then I know I would have more confidence on what to recommend.

As it is, I am a bit concerned about how it was hooked up to get those LEDs to light up "dimly", especially if they remained dimly illuminated. That does not sounds to me like it is hooked up correctly and could, potentially, be damaging.

If, after inserting a battery, there is no voltage on the PC Synch connectors, and, that is the way it is supposed to function, it is a very different situation than I am used to seeing. I am used to a trigger pulse of ~4-6V at the contacts. From there, it is easy to get to the LEDs.

Edited to added: That is, the flash unit will put the voltage on the contacts and the camera will short them. But, the mechanism to short them is inside the camera and I do not think it is mechanical in this case, I think it is electronic but I could be wrong.

That is why I want to see the contact action with a battery - to see if the battery provides current to electronically short the contacts.
 
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