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Thursday, October 6, 2011

Astable mode

An astable circuit has no stable state - hence the name "astable". The output continually switches state between high and low without without any intervention from the user, called a 'square' wave. This type of circuit could be used to give a mechanism intermittent motion by switching a motor on and off at regular intervals. It can also be used to flash lamps and LEDs, and is useful as a 'clock' pulse for other digital ICs and circuits.

Monostable mode

A monostable circuit produces one pulse of a set length in response to a trigger input such as a push button. The output of the circuit stays in the low state until there is a trigger input, hence the name "monostable" meaning "one stable state". his type of circuit is ideal for use in a "push to operate" system for a model displayed at exhibitions. A visitor can push a button to start a model's mechanism moving, and the mechanism will automatically switch off after a set time.

Bistable Mode (or Schmitt Trigger)

A bistable mode or what is sometimes called a Schmitt Trigger, has two stable states, high and low. Taking the Trigger input low makes the output of the circuit go into the high state. Taking the Reset input low makes the output of the circuit go into the low state. This type of circuit is ideal for use in an automated model railway system where the train is required to run back and forth over the same piece of track. A push button (or reed switch with a magnet on the underside of the train) would be placed at each end of the track so that when one is hit by the train, it will either trigger or reset the bistable. The output of the 555 would control a DPDT relay which would be wired as a reversing switch to reverse the direction of current to the track, thereby reversing the direction of the train.

Friday, August 19, 2011

audio calculation

Home Theater - Science of Sound - Components

Speaker Sensitivity , Decibels, Speaker Systems
Determine the amplifier requirement in watts to produce the desired loudness in decibels (dB)
What is the maximum output in decibels (dB) of your speakers based on their sensitivity and power rating?
Determine amplifier requirements to produce desired volume with multiple speakers and variable distance
Determine amplifier requirements to produce desired volume with multiple speakers, variable distance, and placement
Will the new widescreen TV fit? Check out this screenwidth calculator...

Background Info
1decibel (dB) is roughly the smallest change we can perceive.
Doubling the amplifier wattage results in ONLY a 3dB increase in volume ("slightly louder"). Switching from a 50 watt amplifier to a 100 watt amplifier or from a 100 watt amplifier to a 200 watt will only increase the volume by 3 dB as long as you use the same speakers.
In order to double the current volume requires roughly a 6 to 10 dB increase. A 6 dB increase requires 4 times the power! and a 10 dB increase requires a 10-fold increase in amplifier power.
Perceptions of Increases in Decibel Level
Decibel: The decibel (abbreviated dB) is the unit used to measure the intensity of a sound.
(Key points):
1) On the decibel scale, the smallest audible sound (near total silence) is ~0-1 dB.
2) A sound 10 times more powerful is 10 dB.
3) A sound 100 times more powerful than near total silence is 20 dB.
4) A sound 1,000 times more powerful than near total silence is 30 dB.

* Near total silence - 0 dB
* A whisper - 15 dB
* Normal conversation - 60 dB
* A lawnmower - 90 dB
* A car horn - 110 dB
* A rock concert or a jet engine - 120 dB
* A gunshot or firecracker - 140 dB

Imperceptible Change - 1dB
Barely Perceptible Change - 3dB
Clearly Noticeable Change - 5dB
About Twice as Loud - 10dB
About Four Times as Loud - 20dB

[Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure.]
dB SPL laws
Impact of the various changes on sound levels
Double amplifier wattage - increase of +3 dB
Double number of speakers - increase of +3 dB
Double distance from sound source - Decrease of - 6 dB
Halve distance from sound source - Increase of +6 dB
Double driver excursion - increase of +6 dB (note: Equivalent to doubling wattage and # of speakers)

-----Placement of Speakers--------------
Place speaker on the floor - increase of +3 dB - half loading
Place speaker on floor, and against a wall - increase of +6 dB - quarter loading
Place speaker on floor, near a wall, and in the corner - increase of +9 dB eighth loading

audio calculation