Laboratory 4 – Motor Control using Semiconductor

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Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 1 Laboratory 4 – Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier Name  Farhan Ishraq Student Number  31234917 Lab Group  L2B Date of Experiment  2nd April, 2024 Lab Partner  Adarsh Govindan

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 2 Pre-Lab There was no prelab assignment due for this lab. The image above shows that I did the required reading before the lab as mentioned in the lab assignment.

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 3 The datasheets that were used for the lab: Hall-effect sensor: https://fwbell.com/wp-content/uploads/2017/04/Hall- Generators-catalog-NEWER.pdf 2N3904 https://www.onsemi.com/pdf/datasheet/2n3903-d.pdf TIP122 https://www.onsemi.com/pdf/datasheet/tip120-d.pdf 1N4148 https://www.onsemi.com/download/data-sheet/pdf/1n914-d.pdf Circuit Breadboard Image The overall circuit design was given to us, premade in a breadboard. The images below show the circuit schematic and the setup. The pinout for the motor and hall- effect sensor is indicated in the lab manual. Task 1: Motor Switching Part 1 Purpose : Determine the inverter function and operation of Q1 Procedure : Figure 1 Overall Circuit Design Figure 2 Overall Circuit setup

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Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 4 From figure 1, disconnect points A and B. We are left with the circuit below. Using the circuit above, we measure the output voltage for 0V (low state) and 0.7V (high state) . We measure the voltages using the digital multimeter. Results : From the measurements we get the following: 0 V 2.53 V 0.7 V 30.78 mV Using the measurements, we can confirm that the circuit is working like an inverter. Part 2 Purpose : Determine the switching of the motor Procedure : From figure 1, reconnect point B. We are left with the circuit below. Figure 3 Inverter Circuit V O V I V I V O

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 5 Set the distance between the motor and the hall-effect sensor to 5mm and keep the input voltage, , at 0.7V. Vary the input voltage between 0.7V and 0V and observe the powering of the motor. Results : The table below summarizes the observation. Observation 0.7V The motor is off, i.e. no movement/rotation decreasing to 0V The motor turns on and the motor speed increases 0V The motor rotates and the speed is maximum. The observation confirms that the motor power is controlled as expected. The motor is on when the input voltage is 0V and is slows down as we increase the input voltage until 0.7V when it fully turns off. Task 2: Sensor Signal Amplification and Peak Rectification for Motor Control Part 1 Purpose : Establish a 10mA constant, bias DC current through the hall-effect sensor Figure 4 Motor switching circuit V I V I

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 6 Procedure : Connect the hall-effect sensor connector to the circuit as shown in figure 2. (red) connects to the 1k resistor and (green) connects to ground. Remove the 100nF capacitor until the current measurement is taken. After that, put it back into the circuit as it was. To measure the current through the sensor, measure the voltage across the 1k resistor and calculate the current using Ohmʼs Law. Results : We found that the voltage across the 1k resistor is 6.44 V. So, the current across the resistor and hence, across the hall-effect sensor is  6.44 mA. This current is acceptable for DC bias current for the sensor as it is close to the required 10 mA. Part 2 Purpose : Capture the signal generated at the sensor output with the motor running Procedure : From figure 1, disconnect point C. Our goal is to measure the output signal at . Keep point A disconnected and supply 0V to the base of Q1. This will ensure the motor is on for our measurements. Place the sensor 2mm away from the rotating wheel and turn the motor on with 2.5V supply. We capture the output signals using an oscilloscope. Repeat with the sensor placed 5mm away from the rotating wheel. Results : 2mm away The capture below shows the waveform of the generated output signal. I (+) C I (−) C 1 k 6.44 V V (+) H

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Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 7 From the capture, we measured the following values. Max Peak Min Peak Period Peak to Peak 1.51 V 1.47 V 1.82 ms 0.04 V 5mm away The capture below shows the waveform of the generated output signal. Figure 5 Output signal with sensor 2mm away Figure 6 Output signal with sensor 5mm away

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 8 From the capture, we measured the following values: Max Peak Min Peak Period Peak to Peak 1.51 V 1.50 V 1.82 ms 0.01 V Part 3 Purpose : Measure the amplified signal and compare the measured and theoretical gains Procedure : From figure 1, reconnect point C and disconnect point D. With this, we have the following circuit. Keep point A disconnected. Place the sensor 2mm away from the rotating wheel. Ensure 0V is supplied to Q1 and the motor is turned on via the 2.5 V supply. We measure the amplified signal at the output, point D (at ), using the oscilloscope. We also measure the current through the 3.9k resistor. We measure the current by measuring the voltage across the resistor and then using Ohmʼs law to calculate the current through it. Repeat for the sensor placed 5mm away from the rotating wheel. Figure 7 4Rʼs CE amplifier R L I C

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 9 For the theoretical gain calculation, we used the following circuit diagram and the small signal equivalent circuit. The for Q3 is 202. Results : 2mm away From the capture, we measure the following for the amplified signal: Max Peak Min Peak Period Peak to Peak 2.76 V 1.88 V 1.72 ms 4.64 V We see that the peak-to-peak got amplified from 0.04V to 4.64V. This confirms the operation of the amplifier circuit. β Figure 8 Amplifier Circuit Figure 9 Small Signal Equivalent Figure 10 Amplified signal at 2mm

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Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 10 We also measured the current through . 6.4 V 3.9 1.64 mA For the gain calculations, please refer to Appendix (at the end of the report) . We calculated our measured gains to be: Gain Value Measured 116 Theoretical 172 We can see that the measured gain is almost close to the theoretical gain. The discrepancy could possibly be due to the noise in the small signal from the sensor as we can see in figure 5. This also accounts for the distorted shape of our amplified output signal in figure 10. 5mm away From the capture, we measure the following for the amplified signal: R C V C R C I C k Ω Figure 11 Amplified signal at 5mm

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 11 Max Peak Min Peak Period Peak to Peak 1.00 V 0.760 V 1.72 ms 1.76 V We see that the peak-to-peak got amplified from 0.01V to 1.76V. This confirms the operation of the amplifier circuit. We also measured the current through . 5.8 V 3.9 1.49 mA For the gain calculations, please refer to Appendix (at the end of the report) . We calculated our measured gains to be: Gain Value Measured 176 Theoretical 172 We can see that the measured and theoretical gains are similar. This is different from the measured gain for 2mm and it could be because we noticed very little noise when the sensor was 5mm away compared to 2mm away. So, a lower noise level will have smaller impact on the gain of the BJT. Part 4 Purpose : Measure the DC voltage level at the output of the rectifier Procedure : From figure 1, reconnect point D and keep point A disconnected. With this, we have the following circuit. R C V C R C I C k Ω

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 12 Place the sensor 2mm away from the rotating wheel. Supply 0V to Q1 and ensure the motor is turned on with the 2.5V supply. Measure the voltage level at the output of the peak rectifier which is after the diode, at the 33 capacitor. Repeat for the sensor placed 5mm away from the rotating wheel. Results : The following table summarizes our observation. Sensor to wheel distance DC Voltage Level 0.2 mm 2.76 V increasing distance to 0.5mm Voltage level decreases 0.5 mm 520 mV From the table, we can see that as the sensor moves far away from the wheel, the voltage level decreases, which indicates that the voltage supplied to Q1 will decrease and wheel will turn faster. In addition, since there is no load after the rectifier circuit, the voltage levels are higher than expected. In part 5, we will see that the voltage levels will be much lower. To find the voltage drop across the diode, we use the measurements when the sensor is 5mm from the wheel since that is when the motor is theoretically supposed to be on and at 0.2mm it should be off. So, at 5mm, the voltage before Figure 12 Amplifier and rectifier circuit μF

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Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 13 the diode is 1V and after the diode, it is 520 mV. So, the voltage drop across the diode is 0.48V. This is with no load connected to the rectifier output. Part 5 Purpose : Describe the function of the circuit and the dependence of motor operation on the distance Procedure : From figure 1, reconnect point A. With this, we have the overall circuit in figure 1. Place the sensor 2mm away from the rotating wheel. Measure the voltage level at the output of the peak rectifier which is after the diode, at the 33 capacitor. Repeat for the sensor placed 5mm away from the rotating wheel. Results : Since now that there is a load connected to the rectifier output, we will see that the DC voltage levels at the rectifier output will be much lower. Sensor to wheel distance DC Voltage Level 0.2 mm 640 mV increasing distance to 0.5 mm Voltage level decreases 0.5 mm 280 mV From this, we can find the new diode voltage drop, which is Similar to our observation in part 4, as we increase the distance of the sensor from the wheel, the voltage level decreases. In our observation, we saw that the DC voltage level (output of the rectifier) never reaches 0.7V no matter how close we bring the sensor to the wheel and hence, the wheel never fully stops but slows down to a certain speed since the voltage level clips to 640 mV. Now that we have the whole circuit complete, the description below explains the mechanism of the motor control. μF 1 − 0.28 = 0.72 V

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 14 Description : The main purpose of the circuit is to control the power to the motor based on the distance from the wheel to the sensor. The wheel has magnets attached to it. As the wheel rotates, there is a magnetic field around the wheel. This magnetic field can be detected by a hall-effect sensor. The hall-effect sensor outputs a signal bases on the strength of the magnetic field. The magnetic field is stronger closer to the sensor and weaker away from the sensor. The signal outputted by the sensor is a small AC signal which ranges from 110 mV. To use this small signal for controlling power to the motor, we first amplify it using the 4 Rʼs CE amplifier from mV range to V range. The output of this amplifier is an AC signal. This AC signal is rectified using the rectifier circuit to provide a DC voltage for the BJT inverter. The BJT inverter output drives another BJT which controls the power to the motor. So, when the sensor is far away from the wheel, the sensor output is small and hence, the rectified output to Q1 is small, i.e less than 0.7V. So, Q1 is in cut-off region. So, the output of the inverter will be high and hence Q2 is in saturation region. So, motor is powered on. When the sensor is very close to the wheel, the output of the sensor is large and hence, the rectified output to Q1 is large, i.e greater than 0.7V. So, Q1 is in saturation region and the output of the inverter is low. So, Q2 is in cut-off region and power to the motor is shut off. When moving the sensor from far to close to the wheel, the power to the motor is slowly reduced and the wheel rotation slowly decreases. Appendix Measured Gain We calculate our measured gain using the following formula: So, for the two distances, we get: 2mm away → 5mm away → Theoretical Gain A = v input peak − to − peak amplified peak − to − peak A = v = 0.04 4.64 116 A = v = 0.01 1.76 176

Laboratory 4  Motor Control using Semiconductor Sensor, BJTs Circuits, and Diode Rectifier 15 Figure 8 and 9 show the amplifier circuit and the small signal equivalent circuit respectively. So, to calculate the gain, we use the following equations. So, for the two distances: Parameters Values 0.0656 A/V 3079 2681 3.9 172 g = m V T I C r = π g m β R = in ( + R 1 1 + R 2 1 ) r π 1 −1 R = out R C A = v = v s v o − g ( )( ) m R + R s in R in R + R c L R R c L g m r π Ω R in Ω R out k Ω A v

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Laboratory 4 – Motor Control using Semiconductor

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