Does anybody have a schematics for Compur Electronic shutters ?

GeorgesGiralt · May 31, 2007

Now, an explanation of the functioning... Well, what I understood of it.
On the first picture above, you see the PC flash sync outlet. Just to the right of it there is the cable release socket containing a pallet to fire the shutter. Touching this pallet is a small white tab (a circuit breaker). I guess it is used to power on the device.
The speed is set by connecting a particular resistor to the common, using the brush on the speed ring (removed). On the recess of the second pict, just above the coil there is a contact actuated by the shutter blade lever.
So, when you fire the shutter, the device power on, when the blade open, the switch is actuated and start the timing. During that time, the solenoid is activated, retaining the closing blade lever. At the end of the delay, the magnet is de-energized, and the blades close.
When there is no battery or a failure, the shutter operates at max speed (1/500 sec). With a battery, the shutter stays open for the duration of the selected speed. It is a clever and simple design.
When it was functioning, the shutter was damn accurate. A camera shop owner was amazed to test it, and found it tip-top even at the 1/550 sec setting ! he was really surprised. This is why (and the 32 second setting) I will be glad to have it running again.

AgX · Jun 1, 2007

Georges,

I can't look at those photos, but your description seem to confirm that Struan and me were right at hinting at that simple CR-drain speed control.

Can you tell anything about the wiring of that one-and-only(?) transistor or TO3-something thing?

GeorgesGiralt · Jun 1, 2007

"Can you tell anything about the wiring of that one-and-only(?) transistor or TO3-something thing?"
On the picts, you "may" see only one but in fact, there are 5 of them.
I'm trying to find patent literature for the electronic controlled shutter and I may have found a patent from Compur with a sketch of the electronic circuitry. It is simpler than mine but describe the way to power on the device ... So it may apply to my shutter. I have to read the patent, digest it a bit ... and return to the shutter.
As I've sent them out for a quotation by a skilled repairman having parts, I've plenty of time ....

GeorgesGiralt · Jun 1, 2007

Take a look at this :
http://www.google.com/patents?id=o4p1AAAAEBAJ&dq=Compur+electric

Steve Smith · Jun 1, 2007

Looks like a simple circuit. The timing starts when switch 46 is opened and the capacitor charges up at a rate determined by the resistor 58. When the capacitor has charged sufficiently, transistor 50 turns on and switches off transistor 52 and, therefore, the solenoid. The variable resistor 68 is (I think) to introduce a bit of hysteresis into it so it does not dither at a half way point. i.e. the output will either be on or off. The setting of this pre-set will also adjust the overall timing as it adjusts the voltage on the emitter of the first transistor whilst the coil is energised. Most general purpose NPN transistors will work such as BC546 but I would be tempted to add a diode across the solenoid coil to protect the transistor from reverse emf.

EDIT: I appreciate that you may know all of this already and I don't want to appear patronising!

Steve.

ath · Jun 1, 2007

Steve Smith said:
... but I would be tempted to add a diode across the solenoid coil to protect the transistor from reverse emf.

I was tempted too, but then I realized, that this would compromize the fast shutter speeds. Relais for instance, open fastest, when you allow the voltage to go as high as it wants - a (moderate) high voltage transisitor with a high voltage zener diode across it could be the better solution.

AgX · Jun 1, 2007

Steve, ath,

As far as I can follow the discussion we are talking about a shutter still based on simple CR-drain; but not draining directly via the solenoid but using semiconductor switching. What is the use of that? Achieving more precise working of the solenoid than achieved by the voltage fall-off when the capacitator is emptied?

ath · Jun 1, 2007

AgX said:
Steve, ath,

As far as I can follow the discussion we are talking about a shutter still based on simple CR-drain; but not draining directly via the solenoid but using semiconductor switching. What is the use of that? Achieving more precise working of the solenoid than achieved by the voltage fall-off when the capacitator is emptied?

You mean, an RC driving the soleneoid directly? Well, this simply wouldn't work.
First you need a fairly high amount of energy to drive the solenoid; this would require a HUGE capacitor to store this energy. But the main reason is, if you simply add a soleoid (inductivity) without decoupling (transistor), you get a resonant circuit defined by C and L which works totally different. The transistors 1. decouple the RC and the soleoid 2. amplifiy the current and 3. with the hysteresis provide a fairly accurate, fast and sharp switching.

Steve Smith · Jun 1, 2007

AgX said:
As far as I can follow the discussion we are talking about a shutter still based on simple CR-drain; but not draining directly via the solenoid but using semiconductor switching. What is the use of that? Achieving more precise working of the solenoid than achieved by the voltage fall-off when the capacitor is emptied?

As far as I can tell (not knowing the mechanics of the shutter) it is capacitive charge rather than drain.

When the switch which is shorting out the capacitor is opened, the capacitor starts to charge. When it has achieved sufficient voltage, it will turn on the first transistor and switch off the second.

This threshold is reached when the base of the transistor is about 0.7v higher than the emitter. As the emitter is biased at a percentage of the voltage across the pre-set resistor, the trip voltage will be the pre-set voltage + 0.7v.

With a good quality capacitor and stable resistors, the timing should be repeatably accurate.

Steve.

AgX · Jun 1, 2007

Thank you both.

I always thought that my Minox C worked directly with an CR drain. Have to open it...

Depending on the mechanics such a solenoid wouldn't need to be powerfull, as it would only act as a `bolt´ holding the leaves in position, if the shutter is spring driven and hand cocked.

About that resonance issue: I'm surprised to encounter such in a DC circuit.

GeorgesGiralt · Jun 2, 2007

"Depending on the mechanics such a solenoid wouldn't need to be powerful"
The maintenance manual state that the whole solenoid has to be replaced if it is unable to provide 400 gr force.
The U shaped magnetic circuit is closed by a metallic bar which hold the blades open. When the coil is de-energized, the closing blades pull the magnetic bar out of the reach of the magnet. I assume the lever ratio is made as it need less than 400 gr to hold them open.

AgX · Jun 2, 2007

4N, that is quite a lot. I did not expect the solenoid to hold the blades open directly, but rather a bolting action at peak opening. Yes, I would not run it on a capacitator.

AgX · Jun 29, 2007

By sheer accident I came across a schematig circuit as well as a scheme on the mechanics of an electronic Compur shutter in my private library:
in the 2nd volume of the 4th edition of the L.P. Clerc. In three stages the shutter action is depicted in diagrams as well as a long explaining text.

The wiring is shown as a CR-circuit with in series a switching circuit consisting of two transistors plus three auxiliary resistors and two switches. Shutter solenoid control takes place indirectly via charging action of the capacitator: one transistor switches the current to the solenoid, while the second transistor, controlled by the RC circuit switches the first transistor.

Does anybody have a schematics for Compur Electronic shutters ?

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