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Zero-crossing, line locked Xenon strobe
I thought it might be worth sharing an upgrade to the mod suggested by
Richie for making a strobe synchronous.
I found the basic mod was great for showing when I'd machined off enough
metal for the motor to lock, but I couldn't get the phase of the flash
aligned with either the start or peak of a half-cycle, which made it hard to
use for adjusting the gap phase. Racing to the rescue, however, is the
CA3059, a great little chip from Harris which contains a line powered
zero-crossing detector coupled with a triac drive circuit. Requiring only a
current limiting resistor and a small capacitor, this chip is a straight
replacement for the normal RC-diac trigger circuit. The only other changes
required were to reduce the main capacitor from 10uF to 2.2uF (to protect
the flash tube from over-heating), and convert the full bridge rectifier to
a single diode half-wave rectifier (the CA3059 needs to be neutral
referenced, and I wanted 50Hz not 100Hz).
My unit now gives a dead steady 50Hz flash rate, with the phase exactly
lined up with the zero-crossing.
If anyone wants more details feel free to mail me on my home address of
FYI, the CA3059 is ~£1.50 from RS and specs can be found in application note
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: 29 March 2000 00:46
Subject: Xenon strobe for sync rotary
Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk>
In UK and Europe a Xenon strobe kit is available, manufactured by
Velleman Electronics. This unit is sold as a variable speed strobe
and can be bought from Maplin Electronics in UK for only 15 pounds.
The design is really simple and can be converted for synchronous
strobe operation by removing R2 and RV1, and fitting an extra diode
and resistor connected as shown below:
Rectifier end ------->!-------/\/\/\/----- + terminal of cap C2
of resistor R1 1N4007 220K
This causes the Xenon tube to fire every two full supply cycles:
ie. 25Hz for 50Hz countries, (Haven't tried it on 60Hz yet.)
Ideal for viewing both 2 pole and 4 pole synchronous rotaries.
Even in well lit areas, the strobe is bright enough to make
a synchronous disk appear stationary.
For anyone serious about sync gaps I think it's well worth the cash.