Pangolin FB4 Series, User Manual

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26 FB4 User Manual
projector is disconnected from the signal source, there should be NO
light coming out of the laser projector (because there would be no
difference between the differential color signals).
I have recently seen several projectors that used laser diode drivers
that used TTL modulation inputs rather than analog modulation
inputs. TTL modulation basically means that the laser can be fully on,
or fully off. This does not conform to the ISP standard.
However, what’s worse is that the TTL modulation inputs “float
high”, which means that when the projector is disconnected from the
signal source, it produces a full-power, non-moving beam. On a recent
trip, I saw this happen on two separate occasions, by projectors made
by two separate companies. And in both cases, the non-moving full-
power beam landed on dark fabric, which actually caught fire!!
One thing to keep in mind: under very bad circumstances, laser
projectors may present hazards. Projectors must be designed to be
safe, and one of the safety aspects is to prevent light from coming out
of them when the projector interlock is opened, and when they are not
connected. TTL modulation should really be avoided, but if it is used,
at the very least, a differential receiver should be used which would
force the TTL lasers to “float low” instead of “float high”.
Shutter and DB-25 Common Signals
The ILDA DB-25 pin 13 provides a signal to control a shutter, but its
presence is somewhat optional, and may depend on local or federal
laws where the laser projector is to be used. For example, for
projectors that use solid-state lasers, it might be argued that between
the fast and complete extinction offered by the laser diode driver
itself, coupled with the fact that the projector interlock actually
removes the power from the laser diode drivers, a shutter is therefore
not needed. But for ion lasers, even those modulated by a PCAOM, a
shutter would still be desired. In general, it can be said that the shutter