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Northeastern University Department of Electrical and Computer Engineering

EECE 2211: Lab for EECE 2210 Electrical Engineering Lecturer: Iman Salama TAs: Linbin Chen Kan Yao Amine Belkessam

Lab # 5 and 6: IR Remote Control Development and Prototyping

Richard Duchin

Semester: Fall 2016 Date: 12/13/16 Lab Session: Thursday 2:50pm-4:50pm

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Lab Location: 9 Hayden Hall, Northeastern University, Boston, MA 02115

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Content

Page

1. Introduction / Objective

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2. Approach / Procedure

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3. Results and Analysis

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4. Conclusion

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References

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Appendices

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Introduction The objective of labs 5 and 6 was to construct and transmitter and receiver with the capabilities of operating with ambient lit locations. The lab was split up into to portions, the first of which was the constructing the transmitter and tuning it. Tuning it meant that it needed to be able to operate with ambient noise and a variety of different frequency ranges that were produced from the light in the room and the transmitters of the other groups. To differentiate the transmitter, the IR LED was controlled by an astable 555 timer and configured to turn on and off a particular frequency. The second portion of the lab was aimed toward the receiver of this device. A phototransmitter was used to in order to read the signal sent by the IR LED on the transmitter. A variety of filters were used to process the signal. These included a highpass amplifier to remove DC and noise as well as amplify the frequency. Following that, the signal was passed through a bandpass filter configured to the same modulation frequency and then sent to a rectifier. When combining this with a lowpass filter to convert the ac to dc, while the comparator, simultaneously takes the signal and compares it to an adjustable threshold voltage to verify the signal that is received is sufficient enough. This portion of the lab is where the blocks comprised of the flip-flop, relay, and comparator were added. The majority of this lab was dedicated to optimizing the distance that the receiver could pick up the signals sent by the transmitter.

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Approach Due to the complexity of this circuit, the laboratory experiment was broken down into “blocks, each comprised of a different component in the circuit. The first portion, the transmitter was broken down into two major building blocks, the IR LED and the astable 555 timer. The receiver on the other hand was a little bit more complex. The blocks used for this were a phototransmitter, a highpass amplifier, the bandpass, the lowpass filter, flip-flop, comparator and the rectifier.

Constructing the Transmitter: Block 1: Using a 555 timer chip, a circuit was constructed to regulate the frequency of the IR LED output signal. The potentiometer was used to replace the resistors place in the circuit and the frequency was set to 5.2 kHz and verified using the oscilloscope.

Constructing the Receiver Block 2: Highpass amp The highpass amp was the next block that was constructed. Its purpose is to act as a filter, isolating the high frequency portions and all dc components of the signal. More specifically removing low end frequencies such as the ambient light in the room, with frequencies around 120Hz. A schematic of the amplifer is shown below.

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Figure 1: Highpass Amplifier Schematic Block 3: Bandpass Filter The next filter following the highpass amp is the bandpass filter. Its purpose is to allow only a narrow band of frequencies through that are centered around the frequency of the transmitter. This serves the same purpose as to help eliminate the noise being produced from the frequency of the ambient light and other transmitters in the room. Here is a schematic of the bandpass filter. The resistances were chosen specifically to cater to the filtering of the desired frequencies. Using a function generator, the peak frequency was established, which is required to help tune the filter to match our desired frequency. Using the oscilloscope, the midband gain could be measured as well as the bandwidth and verified it was 0.707 points.

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Figure 2: Bandpass Filter Schematic Block 4: Rectifier The rectifier is the next step and its purpose, now that the desired frequency has been isolated, is to actually detect the signal. The signal is currently still in ac form. Through the use if the rectifier and the lowpass filter, the signal is converted into a DC signal. The purpose of the rectifier is to transmit only the positive half of the signal. This is the DC portion of the signal. The remaining negative signal is transported to the lowpass filter, whose function will be explained. A schematic of the configuration is displayed below.

Figure 3: Rectifier Schematic

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Block 5: Lowpass Filter The lowpass filter(as seen in figure above) was used to eliminate the modulation frequency. The resistance and capacitance numbers used in the lowpass filter were calculated to be C=0.01 μF , R3=331572 Ω , R 4=994718=1 MΩ .

Block 6: Comparator The comparator filter served the purpose of comparing the input voltage to a given reference voltage. The value of R was chosen experimentally through trial and error to be 510k Ω and the potentiometer to change reference voltage to the optimal sensitivity level. Using a DMM, the input and output voltages were measured. Here is a schematic of the comparator.

Figure 4: Comparator Schematic

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Block 7: Flip-Flop The next block was the flip-flop, which is a memory device that can switch the output every pulse. Every time a pulse is received, the device will switch to a new output. Using the following schematic, the chip was installed after the comparator and tested for verification by simply toggling the switch and taking measurements of the output states.

Figure 5: Flip-Flop Terminal Layout Block 8 & 9: Lamp & Relay The last components to complete the laboratory experiment were the relay and lamp. They serve to physically and visually verify the validity of our circuit. This was connected after the flip flop. For the goals of the experiment, a distance of 10ft was required between transmitter and receiver. Be altering the values of various resistors in the circuit the distance between the two devices was optimized. A schematic of the relay used is shown below.

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Figure 6: Simple Relay Circuit

Results and Calculations

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Transmitter Calculations Here are the calculations carried out to determine the required resistor and voltage values for the LED circuit. V R =V s −V LED −V C =7.35V

R=

VR =98 Ω I

For the 555 timer: Frequency was set to 5kHz Period=0.693 CT (R 1+2 R 2)

R1=1 kΩ ,

CT =0.02 μF ,

R2=10 kΩ

Potentiometer swapped in for R2 and 555 timer was reset to 5.2kHz Receiver Calculations Block 1: Phototransistor The choice of resistor RE was aided in ensuring that there would be negligible saturation due to ambient light. To successfully achieve this, a 10kOhm resistor was used. When analyzing the waveform on an oscilloscope it displayed a shape of crashing waves. Block 2: Highpass Filter Originally it was designed with a cutoff frequency of 10kHz and a gain of 10, resulting in resistance values of 21830Hz and 218300Hz. However, the system was redesigned using a frequency of 5.2kHz. Using the oscilloscope, the peak to peak amplitude amplified from 9.13 after the phototransistor to 22.3 after the highpass filter.

Block 3: Bandpass Filter Using a center frequency of 7.5kHz, a midband gain of 10, a capacitance of 0.001e-6F and a Q of 10, the bandpass filtered was designed. To determine the resistor values for our desired system with desired frequency of 5.2kHz, the following equations were used. R3 =

R3 Q =1629Ω =30963 Ω R1= 2 Ho π foC

R2=

R3 2

4 Q −2 H o

=619279Ω

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Using the oscilloscope, the bandpass was determined to be B=515 and the 0.707Ho point was determined to be 0.707.

Block 4: Rectifier To design the rectifier values for R1 and R2 needed to be calculated. With a gain of 5, the values turned out to be 1kOhm and 5kOhm, respectively. The input and output waveforms were analyzed using the oscilloscope appeared to look normal. The input had a sinusoidal shape while the output had cutoff frequencies along the centerline of the and the waves were smaller with higher repetition per period.

Block 5: Lowpass Filter To design the lowpass filter a low frequency gain of 3 and a capacitance of 0.1e-6F were using. These were used in combination with the following equations to calculate the resistance values, R3 and R4. The resultant values were R3=331572 Ω f o=

1 2 π R4 C

and R4 =994718 ≈ 1 MΩ . gain=

R4 R3

To test this, the light was completely eliminated and the findings show that the voltage drops to 0V. When light is introduced, the signal immediately jumps to 10V, meaning the amp is sufficiently operating.

Block 6: The Comparator

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As stated in the explanation of the comparator a trial and error method was used to determine the best value for R. The goal was to find a resistance that allowed high sensitivity, while still preventing unwanted switching of the device. To test the circuit’s feasibility, the switch was toggled on and off. It was identified that the dc component of the circuit was -11.25V when off and 440mV when on. This concludes successful operation of the comparator.

Block 7: Flip-Flop Using a flip-flop we apply a memory module to the circuit that allows for storage of the most previous state. With every pulse the output will toggle on and off due to this component. The voltages of the two logic levels at the ouput are 12V and 0V on high and low, respectively. Blocks 8 & 9: The Relay and Lamp By making slight alterations to the sensitivity of the potentiometer in the circuit the distance that the remote could travel while still undergoing minimal interference could be increased. To obtain the farthest distance the potentiometer was turned until the light was on without the transmitter on and then turned back slightly, until it required the transmitter to turn on.

Extra Module: The last portion of the lab required that we make some sort of modification to the circuit to make the lamp light up at a frequency of 1Hz. It seemed pretty clear that using another 555 timer in the transmitter allow for full control of this. We constructing this, the timer was placed after the flip-flop. The resistors used in the construction of the block were 1kOhm and 75kOhm. The component was setup the same way as the one in the original circuit, only the input and ground are reversed to yield a positive output voltage.

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Conclusion The overall goal of this lab was to combine all of the building blocks we have learned during the semester about circuits and circuit components and apply them to create a tangible operating device that serves a purpose. The lab was subdivided into two sectors: The transmitter and the receiver. When constructing the transmitter we were exposed to tuning methods for manipulating frequency using a 555 timer and utilized an IR sensor to transmit the signal. To make this an applicable complex device, we created a receiver that would interpret the signal and use that signal to perform an action, in this case turn on a light. During the construction of the receiver, we were exposed to the concepts of using a phototransistor to take incoming signals and variety of filters to convert the ac signal into a usable dc signal. Filters such as highpass, band, and lowpass filters allowed for us to virtually eliminate any ambient noise that the sensor picked up from surround transmitters and the lights in the room. This experiment was very eye opening into the world of signal processing. This process will deem very helpful when tackling objectives where eliminating noise in signal interception is an issue, which is a very common problem between communicating devices....