Using camera flash sync output

[liion]

Hello,

I'm slowly learning electronic and to do so I am working on a photography related project.
I love the date imprints on photographs and I want to attach an external date back on an analogue camera that doesn't have a date back (yet).

I've already extracted a date module from another camera and l’m able to manually trigger the date imprint process, but I'm having trouble to exploit the camera signal to imprint the date when a photo is taken.
It seems the signal (closing a circuit) sent by camera is too fast to be caught by my date module.

My date module looks like this :


The sync flash I use to receive the camera signal (originally used to trigger flashes):



Firstly, I tried connecting the yellow cables to the sync flash cables

• With one camera (Minolta) : It worked up to a certain shutter speed (1/125s).
• With another camera (Bessa), the one I want to use the date back on : It didn't work, no mater the shutter speed.

Conclusion: camera signal might be too fast I need to slow it down.


Secondly, I tried slowing down the signal using a resistor and a capacitor.

I had no idea what I was doing and tried different capacitor/resistor and had some successes.
Here is an illustration of the circuit :

With 0.1μF and 2KΩ

• With the Minolta : It worked for every speeds ! \o/ .
• With the Bessa, (the one I want to use the date back on) : It didn't work, no mater the shutter speed.

Conclusion: electronic is a complicated science.


My question: How can I exploit the Bessa' signal to trigger the date imprinting?
I am sure the cable and Bessa are working properly since I'm able to trigger a flash using the same camera, cable and socket.


PS: There is this very cool video on how a date back works, for the curious :


Thanks for your help

[AndyBeez]

Respect for using film. I've not seen one of those date backs for decades

As a starting point, I think you-ll need to 'shape' the variable/random length sync pulse through a simple monostable circuit, which then gates the control wires on the date back. You can start by looking into a basic NE555 monostable trigger circuit. Here:
https://www.allaboutcircuits.com/tools/555-timer-monostable-circuit/

[mag_therm]

It could be that the flash contact in the Bessa shutter has corrosion or gum, with resistance not low enough for your circuit.
Best to check with oscilloscope. ( Battery + resistor in series with flash cable)
If you have not previously serviced those old shutters it is better to learn on a scrap shutter first, or else  send to vintage camera specialist.
It would be a pity to ruin the camera.

[bob91343]

It's a matter of time delay.  If the impulse occurs at the wrong time it will not produce the desired effect.  Whether you need to delay it more or delay it less remains to be determined.

[liion]

Thank you all

I ordered some timer 555, I'll update you once I receive them, can't wait!

[nightfire]

Some stuff on those old PC (Pronto/Compur) terminals: Originally the flash was providing voltage from its capacitors to the middle contact and metal frame of the "hot shoe" on top of most cameras.
Attention: Especially with older flashes, this could yield about 300 Volts. Later, in the digital age, lots of flashes used some intermediate circuit to not let several hundreds of volts go stray- later it was 6V, IIRC.
Depending on the camera manufacturer some still claim that they are up to 250 Volts safe, or at least the PC connector on the higher-end models.

In my (photographic) experience dealing with the PC connector and some wireless triggers to interface to them, the connectors of the cables can be troublesome, if the pins are not straight, or dirty.
Here some inspection and cleaning can help a lot on both sides.

The other story is the implementation of flash sync time: In a camera with a classic curtain as a shutter, there is a minimum time where the first curtain has reached its other end, and the second curtain has not yet begun to move. On actual cameras this is around 1/200-1/250 of a second, with older cameras this X-Sync time (Symbol X on some camera elements) could be as slow as 1/30.
So basically when the first curtain is at end, it would trigger the contact, close the circuit of the flash, and the flash will/would fire.
Some older cameras had a "T" option- this was for lightbulbs that needed some moment to ignite, and therefore had to be fired a bit ahead of the arrival of the first shutter curtain.

As some cameras are aware of their X-Sync time, they did not fire a flash when they are outside of this timing.
As the contact from the camera could sometimes only give a very short signal, it is the right approach to get it and give a longer impulse to the data back.

[BeBuLamar]

Please verify the make and model of the cameras you use. Older camera use dry mechnical contact but newer cameras have solid state switch which may not work as well.

[liion]

Hello all !

I've received my timers555 and managed to trigger the date module using the sync flash cable so i'm very happy.
I've followed random tutorials, and it worked. 
Here is the breadboard :

I have a poor understanding of what I did and it seems overly complicated so feel free to correct me !

Maybe I'm crazy but when I touch the camera (it's made of metal) I think I sometimes feel a bit of electricity in my fingers ?

I have one last question

When I use the voltmeter across the two yellow cables of the date module I measure 3v of current.
Do you think there is a way to use this current instead of the AA batteries ? Knowing that when the 2 yellow cables touch each other it triggers a date imprint, so we don't want that circuit to be closed at all times

Thanks again for all your support and good ideas it feels great to spend time on forums like I used to do in the good old days !

[Terry Bites]

Things are very often not as straight forward as they first appear.  The paper version and the real world dont always add up. Electonics always involves some detective work, WTF and details no one ever mentions.
It could be that your device needs a fater rise time or the shoe switch is ifffy or unrelaible (look up switch bounce) or is a "zero volt" contact.
If your 555 circiit works with the 10k pull up then its all good. I might reduce it to 1K. If the current flowing in the swich is very low the contacts may become flaky. A larger current helps by burning off tiny bits of contamination (oxidation) that bild up on the metal contacts.

All the facts about shoes is covered in ISO 10330:2002 but its not free. About $300

Well done for keeping film alive!

[liion]

Hi all !

Thanks Terry !

I was wrong in my previous message, my setup is not really working.
The problem is as soon as I touch the camera it triggers the date imprinting, so there is definitely an issue with my circuit, and current is flowing in the camera.
It also happens with another camera so I don't think it's camera related.

To better show you I made these schematics :
I have no idea of what I did so can you tell me if it looks good to you ?



Thanks 

[RJSV]

Timing that looks nice, here is some alternate methods, you might benefit, if get stuck so far:
   TRY:. As you get other aspects working, don't forget a simple OPTO-ISOLATOR can help, with any headaches around voltage uncertainty.  But I think  that could be OPTO-ISOLATOR LED, at perhaps 10 kohm limiting resistor (to start), and then coupled into any 555 circuit you've got.
   With an opto-isolator you have option of doing any 'wave shaping' or peak-limiting, on a very controlled, low voltage side, isolated, and can effectively only go up to the supply voltage (5 V).