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7/30/2019 IR Blocker
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Experiment
Title :- IR Blocker
Module No :- PHYC40370
Student Name:- Oisin Maguire
Student No :- 09464778
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Abstract:- In this experiment an intruder alarm was developed created
constructed and tested.
Theory:- In this experiment resistors, capacitors, polar capacitors, transistors,
LED(light emitting diode), a photo sensitive diode, a NE567 and an NE555 are
used.
A resistor resists the flow of charge in a linear fashion going by Ohm's law.
IRV
where V is the voltage drop across the resistor, I is the current through the
resistor and R is a proportionality constant which is the factor by how much
the charges were retarded within the resistor itself.
A capacitor stores charge across two plates one of charge Q and the other of
charge -Q which also has the property
C
QV
were C is the capacitance in Farads.
Polar capacitors are capacitors with an implicit polarity it can only be
connected in the circuit in one direction, they also come with a tested voltageas anything above this value can cause a chemical reaction within a polar
capacitor that can cause them to blow up.
A transistor is basically a switch with 3 terminal's, these switches can be used
in logic circuits to compute logic calculations. These 3 terminals are known as
the base(B), collector(C) and the emitter(E). Transistors come in 2 types npn
and pnp. Silicon is a semiconductor and can be doped with gallium or arsenic,
when silicon is doped with gallium this is called p-type semiconductor this is in
which the gallium impurity creates a hole in the electron cloud through the
metal lattice. When silicon is doped with arsenic, arsenic adds an extra
electron to the electron cloud in the metal this is an n-type semiconductor.
For an npn transistor the collector must be more positive than the emitter, the
base emitter and the base collector bout act like diodes. A small current
flowing into the base controls a large current flowing into the collector. For the
pnp transistor all the directions of flow and charge are reversed.
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The diagram to the left is of using
an alternator as a control switch
lighting an led when the voltage
output is positive. The diagram has
the results for a 3 step dc and a sin
wave driving the switch, when the
switch is completes the circuit the
led lights and when the circuit is
broken the led is off. Thus gives the
useful application of the transistor.
If however we want to compute the output of a system with two inputs and a
single output say to confirming that two keys were turned on the ignition of
launching a missile we can use two transistors in series(AND gate), or perhaps
having the transistors in parallel(OR gate) so the if either switch is on the
device at the end is on.
The above diagram has the circuit diagram for bout the AND and the OR logic
gates, with the respected inputs and outputs below. These are included as they
are easy to understand and its an application of transistors.
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A NE567 is a phase lock loop in which its main purpose is to drive a load if a
frequency is repeated within its detection band width. The NE567 comes in a 8
pin duel in line package (dip).
The image to the left is of a 8 pin dip, the 8 pins
are numbered anticlockwise looking down on the
package to the left of the semi-circle as in the
diagram below.
The pins on the NE567 are pin 1 output
filter, pin 2 low-pass filter, pin 3 input, pin
4 supply voltage, pin 5 is timing element,
pin 6 timing element, pin 7 is ground and
pin 8 is output.
A NE555 is a classic timer chip, as well as the NE567 the NE555 has an 8 dip
design. Pin 1 is ground, pin 2 is the trigger, pin 3 is the output, pin 4 is rest, pin
5 is control, pin 6 is the threshold, pin 7 is discharge, pin 8 is Vcc (Voltage
collector collector). When power is applied to the NE555 the capacitor
discharges causing the output to go high, this causes the discharge transistor
to turn off causing the capacitor to begin charging again. The output of theNE555 is a square wave of arbitrary width.
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The diagram below is of the infra red led in which the output is square wave
pulsed modulated by the potentiometer and the 15kilohm resistor. When the
output of the NE555 is high the transistor switch is on and current flows
through the resistor and the two led's light up. When the output of the NE555
is low the transistor switch is off and the two led's are off. C2 is a decoupling
capacitor in which noise from the rest of the circuit is dissipated through the
capacitor as to stop too much noise interfering with the rest of the electrical
circuitry.
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The diagram above is of the sensor and alarm part of the circuit. The input to
the alarm part of the circuit is either high in which case the alarm sounds or is
low in which case the alarm is silent. The PLL or phase lock loop, locks on to a
periodic wave form that if cycled causes the PLL to send out a high voltage to
the alarm. The 4kHz Tone Amp has two capacitor in which they charge and
discharge rapidly when the photodiode detects infrared light the output of the
tone amp is high and when the photodiode does not have any light incident on
it the output of the 4kHz is low and anything in between will result in a pulsethat is linearly dependent on the intensity of the incident light. Since the
refresh rate of the 4 kHz tone mp is faster than the PLL circuit it acts almost
instantaneous with respect to the PLL circuit.
Therefore as the sensor and alarm picks up the output of the infra red alarm
led the alarm is off but when the sensor and alarm doesn't pick up the infra red
alarm the alarm is on thus we have an intruder alarm.
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Construction and troubleshooting:- Construction of the prototype was made
on a standard circuit board with the connection between the electronic parts
and the circuit board being made by solder. Initially when the led circuit was
made there was a low voltage drop across the LEDs although the LEDs were
very bright indicating that there is a high current flowing through the LEDs this
infers that there was a short in the circuit and indeed there was a short in
which the voltage input to the NE555 was not correctly soldered onto the
circuit board and as such caused a large current through the LED's. This was
fixed by resoldering the connections and the voltage drop across the LEDs
greatly increased and the current through the LEDs dropped. The output of
the pulse from the LEDs were modulated by the potentiometer the pulse
width of the LEDs was of the order of 20 microseconds with a relax time of theorder of 200 microseconds.
The proper circuit was created by etching away cooper on a plastic sheet.
Were first the circuit is illuminated by ultraviolet light for 6 minutes and then a
layer of chemicals is burned off by using another chemical, then the etching is
do in a vat were the unprotected metal is boiled off, this leaves the circuit that
was illuminated by the ultraviolet light. Holes were drilled into the etched
material as the electrical components can fit into the holes and then besoldered into place to complete the electrical circuit.
The proper circuit after all the components were soldered into place worked
perfectly first time even up to a separation of over 1 metre after swapping out
the 15k resistor with a 10k resistor in the emitter circuit as to increase the
overall distance that can be achieved between the two circuits.
Above to the left is a picture of the prototype infrared emitter and above tothe right is of the prototype alarm.
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Above is a picture of the alarm after the plastic has been etched drilled and the
components soldered into place.
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The above diagram is of the emitter circuit after the plastic has been etched
drilled and the components soldered into place.
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The above diagram is of the Tina schematic of the infrared emitter of which the
red line was printed onto a transparent medium and used in the etching
process.
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The above diagram is of the alarm circuit, it only has the parts of the circuit
that were left on the plastic medium as the rest of the copper surface will be
etched away.
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Testing and Optimisation:- The prototype was tested and the distance
between the emitter and the receiver was around 3centimetre on the other
hand on the actual emitter and receiver the initial separation was around 30
centimetres, the 15kilohm resistor in the emitter circuit was swapped out and
replaced with a 10kilohm which causes the pulse width and separation to
decreases and makes the signal standout more so than the background
infrared light thus making it easier for the 4kHz tone amp to pick up the signal
and send it to the PLL this changed the maximum separation of the emitter and
receiver from 30 centimetre to just over 1 metre which is more than sufficientfor any doorway or any other place that would need an intruder alarm.
Conclusion:- Commercial electronics can be made at a fraction of the cost of
the product on the shelves but there is a higher reliability rate as there is
generally a limited warranty on electrical devices and as such there might notbe a saving between building and buying electrical devices unless your
proposes is very pacific and as you can easily change the design of the
electrical devices you create yourself it is handier for customisation and
expansion.
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Appendices:-For resistors in series the reisitance of the resistors add in the
form
i
irR
as the current has to flow through each resistor in the series of resistors. The
equation above demonstrates that if you add on a resistor with a high
resistance the current drops across the series of resistors.
For resistors in parrallel if you add more resistors the total current through the
resistors increases as the charges can flow through more resistors like a river
can flow through many streams and if the river can flow through more streams
keeping the impeadance of each stream the same therefore the more streams
the faster the total water will flow out of all the streams. plotting the amount
of streams on an x-axis and the resultant water flow on the y-axis a
logarithimic curve is drawn. This logarithimic curve is true since if you have no
streams for the river to flow the water cannot flow just like charges in the
wires connecting resistors also there is a limit to how much water or current
can flow through anything as there is no infinite charge source.
For capacitors
dt
dV
CI
Idt
dQ
CVQ
which means if the voltage across a capacitor is changed there is a resulting
current directly proportional to the change in voltage. In this case the
proportionality constant is the capacitance of the capacitor.
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References:- The advanced laboratory manual
The art of electronsics by Paul Horowitz and Winifield Hill