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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