What are the most effective materials that can be used to block infrared (IR) signals emitted by a TV remote control? - Design of a Control Circuit Remote Infrared Sensor

Abstract: When I watch TV, I often wonder how the signal sent by the remote control can travel by an invisible path to reach the receiver some 2 metres away. But what if that invisible path was blocked off using particular materials? Would the signal still reach the receiver?

Hypothesis: Transparent materials such as glass and thin, pallid materials such as paper, tissue and linen are the least effective, while solid materials such as wood and metal will be most effective in blocking off weak IR signals emitted by the TV remote.

Aim: To test which materials are most effective in blocking off signals emitted by a standard TV remote control. And to determine if thickness of material plays a role.

Variables:
Independent variable – materials tested
Dependent variable – signal blocked or unblocked
Controlled variables – remote control (strength of IR signal), TV set (receiver), distance and general location of where the IR signal is emitted, angle of remote, thickness of material, width of material, distance between the front of the remote and the material, button on remote.

Risk Assessment: 
According to internet source:
http://home.t-online.de/home/manfred.bromba/indicard/iriexpe.htm
1	don’t look directly into a beam of IR light and avoid eye damage by using UV goggles.

Equipment: 
1	1 standard TV remote control
2	1 hard cover book (encyclopedia size)
3	1 TV set which corresponds with TV remote
4	Ruler with “mm” markings
The following materials: 1 pack of blank paper, 3 sheets of transparent glass (5mm each), metal (copper alloy), slate, Playdohä, leather samples, folded bed sheet linen, folded 100% cotton towel, wood, ceramic (china), latex rubber, plastic rulers, tissues (serviettes), hard foam (mousemat), packaging foam.

Method: 
1.	Stand at a distance where the receiver can receive signals emitted by a remote control – keep this distance constant.
2.	Hold the remote at a 90° angle – place it on top of a book or any other flat surface, making sure the surface is flat and not tilted to an angle.
3.	Using any material with a thickness of 5mm or by tightly compress those materials with several pieces (ensure the thickness is uniform), place it directly in front of the remote’s IR pathway so that the material touches and spans the width of the front of the remote (leave no airspace).
4.	Aiming the remote at the centre of the TV, press the same button 3 times, with a 5 second break in between.
5.	Repeat the last 2 steps with as many possible materials, pressing the same button from the same location each time.
6.	Repeat the experiment using the same materials, doubling the thickness each time. i.e. testing 3 thicknesses: 5, 10 & 20 mm.

Results:

Materials	Thickness (mm)	Signal Blocked	
Control - no material	0	û	û	û	
	5	ü	ü	ü	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	û	û	û	
	10	û	û	û	
	20	û	û	û	
	5	ü	ü	ü	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	ü	ü	ü	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	ü	ü	ü	
	10	û	ü	ü	
	20	ü	ü	ü	
	5	ü	û	ü	
	10	ü	ü	ü	
	20	ü	ü	û	
	5	ü	ü	ü	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	ü	û	ü	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	ü	ü	ü	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	û	ü	ü	
	10	ü	ü	ü	
	20	ü	ü	û	
	5	û	û	û	
	10	ü	ü	ü	
	20	ü	ü	ü	
	5	û	ü	û	
	10	ü	û	û	
	20	ü	ü	ü	
	5	û	û	û	
	10	ü	ü	ü	
	20	ü	û	ü	
	5	ü	ü	ü	
	10	û	ü	ü	
	20	ü	ü	ü	
	5	û	û	û	
	10	û	û	û	
	20	û	û	û	

Conclusion:
Of the materials tested, those which are transparent or have a high occupancy of airspace such as glass and foam respectively, are the least effective in blocking off IR signals emitted by the TV remote. In contrast, those which are most effective for this purpose are wood, metal, paper, cotton towel and leather.

Discussion:
My first attempt at this experiment failed because, originally, I had proposed to leave a 5cm gap between the material and the emission part of the remote. This didn’t work as none of the materials were blocked. So, upon making the necessary modifications, the experiment was successfully executed.

Having said this, my experiment was successful because I made use of repetition to ensure the reliability and validity of my results. I have also compared my results to those of others through browsing the internet. Since others had obtained similar results – that transparent materials and those with a high occupancy of airspace are least effective in blocking off signals by a TV remote – I have proved that my results are reliable. By using an appropriate measuring device, a ruler with “mm” markings, I have also justified the accuracy of my results.

Although this experiment was a success in that I correctly tested my aim and hypothesis to deliver the expected result, there would still be elements of design which can be improved. If I performed this experiment again, I would ensure that the remote be placed directly from the centre of the TV, not just any location. This would ensure a clearer signal, resulting in more accurate results and contributing to the experiment’s overall efficiency. Also, the width of the material is irrelevant to the experiment and does not need to be controlled. Furthermore, the remote should be placed on a stationary surface e.g. coffee table, instead of balancing a book on one hand. This would avoid tilt by encouraging a level surface, which could possibly affect the accuracy of the results. Another aspect would include taping together any loose material instead of compressing them with my fingers. I believe these factors had led to minor flaws in the accuracy and reliability of my results.

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Remote Infrared Circuit
Introduction
For my electronics project I chose a circuit that would incorporate an infrared sensor, which would pick up infrared coming from an infrared transmitter/source. This would lead to a motor or LED becoming operational.
I started off by using the Internet to research information on infrared sensors and transmitters. Once I had collected enough research and understood the principles behind infrared and how it worked I could start constructing my actual project on breadboard.
However before constructing the actual project I had to firstly make a preliminary project substituting the infrared components for an LDR with a light source. This would allow me test the circuitry and collect readings while allowing me to better understand the principles of the circuit and the components while deciding whether the concept of the circuit would be feasible. Then once this stage of my project is complete and the circuit is found to be reasonable I will substitute the LDRs for infrared sensors.
Specifications
My preliminary circuit senses a change in light intensity(By utilizing a LDR and resistor in a potential divider arrangement) and then, with the use of a D type flip-flop acting as a latch, sends a voltage to an LED or motor. An optional addition to the circuit is to have another LDR in another potential divider arrangement that resets the whole circuit when it senses a change in light intensity. I chose to use potential divider circuits in my project because they would produce me with the correct range with which the D type flip-flop can operate with to produce the required outputs
The intended circuit has an infrared sensor with a resistor in a potential divider arrangement detecting an infrared signal or a rise in infrared and with the latch send a voltage to an LED or motor. This circuit also has the addition of another infrared sensor in a potential divider acting as the reset mechanism.
I intend to have my whole circuit operating off a power supply of 5 volts. The chip I used is 7474 which incorporates two D type flip-flops. I used this chip because I will be using it in the circuit as a latch so that when it receives a clock pulse it will let a high voltage through . To set the chip, pin 4 has to detect a change of low to high voltage (0.8v-2v). To reset the chip, pin 1 has to detect a change of high to low voltage (2v-0.8v). The infrared sensors I used for my circuit gave out a high voltage of about 4V when sensing infrared and a low voltage of about 0.2mV when in the dark. 
For my preliminary circuit the LDR I used for the setting of the circuit had a resistance of 960Ω when in light and a resistance of 5.2KΩ when in darkness. I used a resistor of 4.7KΩ with it in the potential divider. I calculated what value the resistor would be by using the formula: V=I*R.
Resistor value:
In light: 23000+4700=27700Ω
5/27700=1.8e-4I 
1.8e-4*4700=0.85V 
In dark: 5200+4700=9900Ω
5/9900=5.1e-4I
5.1e-4*4700=2.37V 
This potential divider has a voltage output of 0.85V in the light and 2.37V in the dark.
The LDR I used for the resetting of the circuit had a resistance of 270Ω in the light and a resistance of 1.4KΩ in the dark. I used a resistor of 270Ω with it in the potential divider. The calculations for the resistor are:
In light: 350+270=620Ω
5/620=8.1e-3I 
8.1e-3I*270=2.21V 
In dark:1400+270=1670Ω 
5/1670=2.9e-3I 
2.9e-3*270=0.81V
This potential divider has a voltage output of 2.21V in the light and 0.81V in the dark.
For my final circuit the infrared sensor I used for the setting of my circuit had to be placed into a transistor switch arrangement because of the behaviour of the infrared sensors. I put a resistor in a potential divider arrangement with the IR sensor with a value of 100KΩ and another resistor at the output of the transistor with a value of 2.2KΩ. However due to the time constraints I was unable to construct another transistor switch with an IR sensor as the resetting mechanism of the circuit. I used the transistor because including an IR sensor in a potential divider will not present me with the required outputs, as a result I used the transistor to deal with the unusual behaviour of the IR sensor.
Finally I decided that I would use an LED as an indication of the state that the circuit is in. I wired the LED to a 100Ω resistor in series so that the voltage across the LED would be 1.7V and not 5V which would be too high for the LED. The transistor I used was a Bc 109 and had the pin setting of 1=emitter, 2=base and 3=collector.
The circuit
Test Results 
I firstly began testing by checking whether my D type flip-flop worked or not. I did this by wiring up the chip to a power supply of 5V. then wired up the set(pin 2) on the chip to a 5V and I connected the output of the chip(pin 5) to the external voltmeter on the bench. I then wired the clock input of the chip(pin 3) to 5v. When this was done the output of the chip changed from 0V to 5V indicating that the setting of the chip worked correctly. I then earthed the reset (pin 1) of the chip while disconnecting pin 2. this led to the output reverting back to zero. This meant that the resetting of the chip worked correctly as well.
I also tested whether the potential divider portions of the circuit worked correctly. I connected the setting potential divider up to 5V and the output to the voltmeter on the bench. When the LDR was uncovered the voltage output was 0.85V, while when it was covered the output was 2.37V. This meant that the setting potential divider would correctly set the chip. I then tested the resetting potential divider with the same method and found that when the LDR was uncovered the output was 2.21V while when it was covered the output was 0.81V. This part of the circuit was also compatible with the chip and would successfully reset the circuit.
I then tested the infrared sensors. I did this by wiring them up to 5V and the voltmeter on the bench. When there was no infrared source the output of the sensors was 4.8V while the output when using an infrared source was practically 0V. This meant the sensors were working to their specifications. I also tested the transistor by placing it upon the testing socket on the multimeter and setting it to hfe. The reading given out was 500 which was within the range of 200-800 which I was expecting meaning the transistor worked.
The final tests I did involved having the whole circuits wired up to 5V. with the preliminary circuit when the reset LDR was covered and the setting LDR was uncovered the LED would light up meaning the setting of the circuit worked( 5V was coming from the output of the chip when measured). I then covered the set LDR and uncovered the reset LDR. This time the LED went out meaning the resetting of my circuit worked. This meant the whole circuit worked and I could move onto the intended circuit with infrared sensors.
I then replaced the setting potential divider with the infrared/transistor switch. When the reset LDR was covered and the IR sensor received infrared the LED came on. This meant the switch and IR sensor were working to set the circuit. I then removed the IR source and uncovered the reset LDR the whole circuit reset. Due to the time limit I couldn't replace the resetting potential divider portion of the circuit. 
Assessment of performance
In the end both my preliminary and final circuits worked. With the circuit containing the LDRs the circuit worked exactly to my specifications and worked 100% of the time. The setting and resetting of the circuit worked during every test of the circuit while each component passed their individual tests.
The second circuit didn't fully reach my specifications. This was due to the fact that I didn't install an IR sensor with transistor switch for the resetting role of the circuit. Therefore the LDR from the previous circuit remained. The setting portion of the circuit did fulfil my specifications and passed tests 100% of the time as well. While the infrared sensor and transistor worked fully to their potential.
Overall the circuits were 100% reliable and fulfilled their specifications I was disappointed that I couldn't replace the reset LDR on the second circuit with a IR sensor.