Texas A&M University at Qatar Electrical Engineering

Transcription

1 Texas A&M University at Qatar Electrical Engineering ECEN 214 Electric circuit Theory Student Name: Mahmudul Alam Semester: Spring 2008 Section: 501 Lab #5 Report Application of Op-Amp: Electronic Security System Design: Part 2 of 2 Group # (4) Team Member: Misam Jaffer Lab Engineer: Engineer Wesam Mansour Date of Experiment: March 2, 2008 Date of Due: March 11, 2008 On my honor, as an Aggie, I have neither given nor received unauthorized aid on this academic work

2 Procedure In task 1, the circuit shown in figure 1 was built. The main element of the circuit was a latch. An IC called CD4044B was used as the latch. The enable button (pin 5) was used connected to high to enable the device. After initializing the circuit, the /ALM button was pressed and the output S, Q and R was measured with Fluke DMM. Pressing the /RESET button, the procedure was repeated. Table 1 lists these data. Figure 1. The Latch (Figure taken from lab manual 5) In task two, the portion of the circuit shown in the box in figure 2 was constructed in the NI ELVIS breadboard. The main elements of the circuit were two LEDs and an operational amplifier. Pressing the /ALM button voltage Q and buffer output was measured by Fluke DMM and the output of LED was observed. The procedure was repeated pressing the /RESET button. Table 2 lists these data. Figure 2. Buffer and LED (Figure taken from lab manual 5) Mahmudul Alam Page 1 of 5

3 For task three, a Printed Circuit Board (PCB) was used. This printed circuit board contained the circuit (Current to voltage converter, signal amplifier, and comparator) that was built in lab 4. The leads of the PCB were connected to ± 12 V. The laser and photo detector was also connected to the PCB. The output of the PCB was connected to pin 7 (S input) of the latch. Finally the buzzer was connected. The completed circuit was checked by the lab engineer. Figure 3 shows the complete circuit of the security system. Figure 3. The complete circuit of the security system (including the buzzer) (Figure taken from lab manual 5) Mahmudul Alam Page 2 of 5

4 Data Tables Table 5.1. Task#1 Data Voltage at (V) S Q R /ALM on (depressed) mv V V /RESET on (depressed) V mv mv Table 5.2. Task #2 Data Q Voltage Buffer Output LED on /ALM on (V) V V Red /RESET on (mv) mv mv Green Table 5.3. Task# 3 With laser beam at the photo detector Without laser beam at the photo detector Comparator Output voltage (Measured) V V Discussion The security system that we designed in the lab sounds an alarm when it detects an interruption in the light beam. However to detect the interaction, the laser diode and the photo detector must remain properly aligned. The circuit of the security system included four operational amplifiers, a latch, two LEDs, and a buffer. The operational amplifiers were used as current to voltage converter, signal amplifier, comparator, and buffer. The procedure of how the security system works is explained in detail in the following paragraphs. Table 5.4 lists all the calculated values. These calculations are also explained in the discussion that follows the table Table 5.4. Calculated Values Laser Diode ON ON Photo detector Receiving Not Receiving Current to Voltage Converter Amplifier 1.07 V V Comparator 12 V (HIGH) Latch Buffer LED LOW LOW Green 0 V 0 V 0.2 V HIGH HIGH Red Mahmudul Alam Page 3 of 5

5 When the photo detector is receiving the signal from the laser diode, the current, as measured by the FLUKE DMM is ma. The amount of converted voltage, calculated according to following formula V converted = -I d (22000).... (01) is V. The amplified voltage, calculated according to the following formula V amplified = (-V converted ) (22).... (02) is V. This voltage, as we see from the graph below that describes how the comparator used in the circuit behaves, is high enough for the comparator to operate in its positive saturation region. Figure 4: V in vs. V out graph for the comparator used in the security system circuit Since the comparator is operating in the positive saturation region, it means output of comparator is 12 V. Therefore, the S input is HIGH. The R input is LOW, because initially the /RESET button was pressed. According to latch truth table, the output Q of the latch is LOW. The buffer output is same as its input Q, so the buffer output is also LOW and that is equivalent of 0 V. That means the green LED will be on. Mahmudul Alam Page 4 of 5

6 Now, /RESET button is released, and the latch inputs (S and R) of the security system are HIGH and HIGH. It means that the condition will remain unchanged, and that is the green LED will remain on. When the beam is obstructed suddenly, current I d is 0 A. So, V converted, if we calculate according to formula 1, is zero. So, V amplified, according to formula 2, will also be zero. From the comparator graph we see that when the input voltage is close to zero, the comparator operates in the negative saturation, which means comparator output is zero. Therefore, the S input is LOW. The R input is HIGH, because the /RESET button was released off. According to latch truth table, the output Q of the latch is HIGH. The buffer output is same as its input Q, so the buffer output is also HIGH and that is equivalent of 12 V. That means the red LED will be on and buzzer will start ringing. If we compare the calculated values with the measured values, we see that there is big difference between the calculated amplified voltage (23.54 V) and the measured amplified voltage (11.24 V) for the beam unobstructed. A probable reason for this difference is op-amp not behaving as an ideal op-amp. All other measured values are very close to calculated values. Conclusion Lab 4 and lab 5 gave us practical idea on engineering design work. To make the lab more enjoyable, I suggest the following: If possible, students should find the calculated value before doing the lab. It will then help them compare the measured value and calculated value while they are performing the lab. Mahmudul Alam Page 5 of 5