Jim,
?
I am
very greatful and appreciate you taking the time to formulate this response. Not
being an electronics expert, your detail has helped me to understand what needs
to be done. Incidently, I am an investigator in the transportation industry and
this alarm will be placed inside of packages. If someone attempts to pilfer the
"test" package, the alarm will sound.
?
Again,
much thanks to you.
?
Sincerely,
?
Kenyon
Jones
?
?
?
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Kenyon,
Thank you for your response. It seems that the photo transistor is
conducting enough to send minimal current through the relay but not enough
to activate the switch, so to speak.
In this case you will
probably require a second transistor, connect the phot transistor with the
collector at Vcc and the emitter on the base of the second transistor. This
way the first tranny provides bias to the second. Put the relay in series
with the second transistors collector and Vcc.
The emitter can go to
ground, i.e. p.s. comnon. These would both be NPN transistors else you can
turn the power supply upside down, i.e. pos. grounded
etc.
My problem is that I
need the circuit to be such that the alarm continues, even if light is
removed from the photo transistor.
This will require a
latching device. If you are using a ralay instead of a solid state device
you can use an auxilliary set of contacts to hold the relay in after the
lighe 'goes away'. Or you could possibly use an SCR (silocon control
rectifier) in place of the second transistor, these devices stay on once
triggered.
Could you tell me more
about "putting the alarm device in series with the collector and
VCC.
This is pretty strait
foreward.? Connect one end of the relay to Vcc (p.s. +)
and the other
end of the relay to the transistor collector. The emitter goes to ground, or
p.s. common.? The base of a photo transistor goes to light, i.e. the
light turns on the transistor.? Or if this is the second transistor it
would be connected to the emitter of the first one.? What I have
described here is a very simplified description. More specifics would depend
on the nature of the devices used, etc.
Jim
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