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volume control allows the light to turn on from a level of 70
db to about 90 db, since we anticipate that smaller groups will
require greater sensitivity and vice versa. The volume control
is a miniature differential that allows 5 1/2 full turns and has
no stop to allow it to last longer and be set to a finer degree
of sensitivity. The circuit boards are driven by a conservatively
rated 12 v dc power unit. Behind the green boards is a master
board that incorporates two 12 volt regulators and a 9 volt regulator
and some timing circuits. The very small board is a pre-amp that
is fed from the black condenser microphone in the red light. The
microphone senses a sound level, and the pre-amp amplifies it
and feeds it to the VU meter board. The first relay board uses
its first relay to keep the green light on when the relay is off.
As soon as the relay is energized from the missing yellow LEDs,
the relay passes 11 v ac power to the second relay board. When
the second relay board is off, the yellow light is on. When the
second relay board is energized from the missing red LED, the
yellow light goes off and the red light comes on. There are about
2 second delays built into the red and yellow relay boards so
the red and yellow lights do not track the sound instantaneously.
Instead they react to an average level of sound and stay on for
the 2 seconds to wait for a reduced average level of sound.
In a small
room you may find that sharp sounds can trigger the lights and
so can a significant vibration. This is because of the room
size. In an auditorium or cafeteria, the sound averages out
and only a very loud handclap or vibration close to the light
will trigger it. The toggle switch in the yellow light can be
used to decrease the sensitivity to hand claps when it is set
to OFF.
The last
relay board accepts signals from the first and second relay
boards to turn on the cycling time delay. On the traffic light,
the buzzer/screamer is loud enough that it could serve to keep
the light on red permanently once it sounds. Instead a time
delay of about 2 seconds is used so the third relay board cycles
on and off at a rate of about 2 seconds. Thus when the light
goes red, the buzzer sounds for 2 seconds. It then goes silent
for 2 seconds so the microphone can sample the room sound. If
the room sound is still sufficient to trip the red light, the
buzzer will sound for another 2 seconds and so on. Be sure to
adjust the control inside the yellow light so that the sounder
does not reach anyoneís ears at a level in excess of 85db.
The mounting
brackets are shipped in a closed position. It is necessary to
remove and reverse them to put the long portion against the
wall. Be sure to use a proper mounting system to support the
15 pound weight of the unit and even the force of a student
tugging downward on the unit.
The light
can be cleaned with ordinary soap and water. Do not allow water
to enter the unit, however. The circuit boards are exposed for
heat circulation reasons. They are sensitive to improper pulling
and tugging, so keep untrained personnel out. There are no internal
adjustments on the circuit boards. The
audio monitor should perform quite well for many years. In the
event that there is a problem with the audio monitor during
the three year warranty period or afterwards, please contact
School Specialties for shipping directions. If you do
not have the original double carton to ship the unit back with,
one will be sent to you at no charge. Shipping the unit back
in any other carton will probably void the warranty.
The two
additional circuit breakers protect the 12 v dc supply and the
11 v ac supply. It is ok for them to trip very occasionally
but if they trip a couple of times in a row, the light may be
damaged and require warranty repair.
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