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Re: noise indicator (details)
Actually i had to depend on available components and circuits in the market
to make the prototype. I am providing whatever i can.
I found a circuit board in the market which is commonly used in a car
It had an amplifier AN7114E with a pre-amplifier from C945 transistors (i
think). To the input where the HEAD is normally attached, i attached a
condenser mike and gave it about 1.5 volts from the nearest point. Where
there was volume control, i soldered a 10K variable.
The output required a speaker for which i had no use (no noise) so i
soldered a 10 ohms 5 watts resistor to it. The power supply to this unit
was a small domestic 500 ma AC/DC 12 volt converter.
What I call a level meter was also something i found in the local shop.
They said it was a replacement part for showing the volume level in a
Player. It has an IC with 9 pins and is marked with AN6884. There are
actually 10 LED's attached to the IC with an amazingly simple circuit with
just resistors. However, i noticed that they were attached in parallel, in
such a way that the glass cover on LED's showed the level going in upposite
directions on either side in five successive levels.
I just gave the output of the amplifier circuit to the level indicator. I
do not know the reason but when i gave the output of the amplifier without
the 10 ohms 5 watts resistors (speaker) to the level indicator, all the
LEDs would go on for ever. This unit also required 12 volts, so i connected
it to the same power supply.
At this stage, with a bit of adjustment of the volume (sensitivity)
control on the amplifier unit, i was able to test the circuit by just
placing the mike in front of my TV and changing the volume of the TV with
the remote control. The LEDs would glow from 1-5 with the level of the TV
The third and final step was to turn the LED glow into a visible display on
the road. For the time being, i have five 12 volts relays attached to the
system with driver circuits through five A564 transistors. Each relay
switches on a 220 volt domestic lamp when the LED glows up (they are
there). The five lamps are nailed on a wooden plank.
The set-up is working as it is. I have tested it on the road too. I placed
it about 15 feet away at a height of about 6 feet with the mike just in the
direction towards the road. Normal traffic kept the lower one or two lamps
flickering, but as the noise would increase, progressively more lamps would
go on. The noise of the faulty bracks was the most sever, i found. All the
lamps went up with it. The next was the whistle of the Cop on duty. On the
average, 3rd and 4th lamps received more hits.
The device has another potential use too. It should not be difficult to
connect a counter to each relay or switching circuit. If the lamps are
properly calibrated for recording noise at specific db level, then the
counter after a month use would autometically identify areas where noise is
more. It can therefore serve as a survey tool.
For actual use, i have the following two points (for the time being) which
i would like to share with you all.
1. The mike, amplifier, level finder, thyristors etc all require proper
checking through instrumentations for prolong and reliable use. Also there
should be proper calibration.
2. The lamps should be enclosed in a proper box with a shape such that the
lights are not confused with traffic signals. The colors shoud also be such
that they are different than the traffic lights. The lower most cell of the
light box should carry a symbolic represtation of noise so that drivers
could see that these lights indicate noise.
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