Thanks much. I figured it was probably the low voltage of the flash but
didn't know why. Now I know why but don't really understand it. :-)
It'll probably take me a month of Sundays to get around to doing it but
I was intrigued by stringing a bunch of diodes together to determine the
actual trigger point. I may do that some time.
While interesting, I'm not sure it would be worthwhile to build
something to reliably trigger the Canyon when I've got other flashes
that do work. The only reason I bought the Canyon was for its autofocus
assist light with on-camera flash.
As to the origins of the electronics in these cheap Chinese radio slaves
I suspect that they are derived from garage door openers. The size of
the transmitter PC board and the use of a 12 volt 23A battery looks like
a near duplicate of my circa 1996 Lift-Master garage door opener.
Chuck Norcutt
Tim Hughes wrote:
> --- Chuck wrote about his problems with rf slave triggers :
>> I ultimately determined that the sync problem is clearly
>> due to a short delay imposed by the slaves
>
> I am guessing but these slave modules likely use a low cost RF chip-set from
> a company like Micrel
> or Maxim (RF div) or even a module from Lynx (based on maxim chip) which can
> introduce a delay of
> something like 100-200us. At 100us I would not have expected the sync to be
> affected for 1/200
> shutter (5ms), since 100us is only 2% of 5mS and the delay of the normal
> flash itself to peak
> output is likely ~1mS or so. Maybe they rolled their own discrete
> transmitter/reciever and it has
> very long delays?
>
>> and much to my surprise, I discovered that the slaves (all 5 of them of
>> 2 different makes) almost don't work at all with the 540EZ.
> ......
>> Is this somehow related to the trigger voltage of the flash unit? My
>> T-32's and Sunpak 422D's are all in the 10-12 volt range.
>
> The T32's are nominally ~11.4V as you mention (zenner regulated), but
> sometimes seem more like
> ~7v(?) if I remember correctly, probably due to zenner leakage as current is
> very low. They can
> appear higher if used with another brand flash (on a connector cable say) as
> they use an isolating
> diode which allows sync pin to rise to the voltage of highest device .
>
> The t20's are protected to 12v by a zenner but the resistor divider is set to
> run it at ~7V and
> there is no isolating diode. (This does mean the t20 should actually protect
> the camera from a
> higher than 12V on the sync pin if used with cable or sync connector.)
>
>> the exact trigger voltage of the Alien Bees other than the spec says
>> "less than 6 volts". The Canyon 540EZ, on the other hand, is about 3.4
>> volts with alkalines and about 3.7 volts on the high voltage battery pack.
> ......
>> I am intensely curious as to why this flash won't trigger with a slave that
>> fires
>> everything else.
>>
>
> It is likely your slaves just don't pull the pin low enough near ground, to
> trigger the newer low
> voltage canyon flashes OR they draw too much current at idle from the pin OR
> maybe the scr in the
> slave does not trigger properly at such a low terminal voltage.
> Most slaves (and many cameras) use a low power scr to pull the sync pin low.
> The scr typically
> pulls the pin to ~1V but if a series diode is added to cause better scr
> switch off (see my
> description /circuit diagram on Mark Dapoz's hardware website : high voltage
> trigger for Q310)
> this becomes more like 1.6V. The change between trigger voltage and idle
> voltage, is then only
> 1.8V. You could actually test the voltage required very crudely by hooking
> up some small diodes
> in series with a piece of wire and shorting the sync pin to ground via the
> diodes. Add more diodes
> to the string until it stops triggering. The voltage it stops triggering at
> is then ~ the number
> of diodes times about 0.5V (within 0.5V!). You would need a scope and a
> variable supply to
> figure if it was the scr not firing at low volts.
>
> You could probably modify the slave trigger with an add-on to trigger the
> canon flash more
> reliably, by using a few extra parts.
>
> Tim Hughes
>
>
>
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