Asshray's EV-RE Level 2 Report
6 / 10 / 2024
Task 1 - LTspice and KiCad
Objective:
Design and simulate an astable multivibrator using 555 timer, and also be familiar with LT Spice & KI Cad.
General Working:
A multivibrator is an electronic circuit used to generate square wave signals. It operates in three different configurations as follows,
| Astable | Monostable | Bistable |
|---|---|---|
| Least Stable | Stable | Most Stable |
| No trigger signal needed | One trigger signal needed for set | 2 trigger signals needed for set & reset |
| Abruptly switches between 0 &1, without any trigger signal. | When there is a trigger signal, the input signal switches from the initial state and remains in the new state for a certain period of time and later comes back to the initial state. | When there is a trigger signal, the input signal switches from the initial state and resets back when the 2nd trigger signal is detected. |
| Application: Blinking of LED | Application: Can be used in timer circuits | Application: Can be used while integrating with LDR to make automatic headlights |
The duty cycles & the timer configurations can be changed by changing the resistor ratio in the above circuits.
Circuit Connections:
Simulations
LT SPICE
KI-Cad
References:
Task 2,3 - Speed & Direction control of DC motor
Objective:
Learn about the dual H-Bridge L293D motor driver and control the speed & direction of the dc motor.
Learning:
Why do we need a motor driver? We need a motor driver to control various needs of the motor like speed & direction as per the user's needs, but if we use microcontrollers directly for these then we may burn them out as we might need to operate the motor at high current and voltage (Above 250 mA). Also the the signals generated by the microcontroller (HIGH(5v) or LOW (0v)) have insufficient voltage to power the motor. Hence, we need a motor driver.
In Level 0 L298N was used here L293D is told, basic differences between the two:
| L293D | L298N |
|---|---|
| Max. of 600mA | Max. of 2A |
| No heat sink | Has heat sink |
| Internal back emf protection, using built in diodes | External back emf protection |
| Suitable for motors with lower current requirements, such as BO motors | Suitable for high-torque and high-RPM motors |
General Working:
- PWM – to CONTROL SPEED
Speed of a DC motor can be controlled by *changing its input voltage*, for this we use Pulse Width Modulation (PWM). It is a technique where the average value of the input voltage is adjusted by sending a series of ON-OFF pulses. This average voltage is proportional to the width of the pulses, which is referred to as the Duty Cycle.
***Duty Cycle is directly proportional to the Speed of the DC Motor***
- H-Bridge – to CONTROL the spinning DIRECTION
The spinning direction of a DC motor can be controlled by *changing the polarity of its input voltage*, to do this we use an H Bridge it is a circuit that is made up of four switches arranged in a H shape, with the motor in the center. Closing two specific switches at the same time reverses the polarity of the voltage applied to the motor therfore reversing the direction of the motor.
Circuit Connections:
| LM298N | Components |
|---|---|
| Output 1 & 2 | Motor 1 |
| Output 3 & 4 | Motor 2 |
| +12V | Battery +ve |
| GND | Battery -ve |
| LM298N | Arduino UNO |
|---|---|
| GND | GND |
| IN1 | 5th Digital pin of Arduino UNO |
| IN2 | 4th Digital pin of Arduino UNO |
| IN3 | 3rd Digital pin of Arduino UNO |
| IN4 | 2nd Digital pin of Arduino UNO |
| First pin of potentiometer | 5V |
| Mid pin of potentiometer | A0 |
| Last pin of potentiometer | GND |
Actual Connections:
References:
Task 6 - Temperature Detection
Objective:
Measure temperature using an LM-35 temperature sensor and Arduino and display it on the serial monitor, taken at intervals of 5 seconds and turn a led on using BJT as a switch when the temp crosses a certain threshold (40°C).
Learning:
The LM35 is an analog low voltage temperature sensor manufactured by Texas Instruments.
| LM35 | Specs |
|---|---|
| Operating voltage | 4V to 30V |
| Current drawn (During temperature conversion to electrical signal) | 60µA |
| Temperature range | −55°C to +155°C (it requires a negative bias voltage to measure negative temperature) |
| Accuracy (@ room temperature) | ±0.5°C |
| Note: But if we need to measure -ve temperatures then it is preferred to use TMP36 temperature sensor as it is able to measure negative temperatures without the need for negative bias voltage. |
General Working:
It is a chip that provides a voltage output that is linearly proportional to the temperature in °C (OP voltage increases linearly by 0.01 V (10mV) 1°C rise in temperature). The circuit triggers the LED when the temperature is >40°C, therefore turns the LED ON.
Circuit Connections:
| LM35 | Arduino UNO |
|---|---|
| GND | GND |
| VS | 5v |
| Vout | A1 |
| BJT | Arduino UNO |
| Base | ~9 |
| Emitter | GND |
| Collector | LED -ve |
| LED +ve | 5v |
Actual Connections:
References:
TASK 7: Temperature and Humidity Detection
Objective:
Measure temperature and humidity using DHT11 and display the readings on serial monitor.
Learning:
DHT11 stands for Digital, Humidity, Temperature sensor
- DHT-11 is a digital temperature and humidity sensor. It outputs a much more accurate temperature reading compared to an analog sensor. The output of the DHT-11 is a digital signal that can be read at Arduino’s digital I/O pins.
- It has 14-pin, 8-bit microcontroller IC.
- It senses temperature in degrees centigrade, ranging from 0˚ to 50˚C.
There are 2 main options when it comes to Humidity-Temp. sensors i.e. DHT11 & DHT22 sensors, their key differences are as follows;
| DHT11 | DHT22 | |
|---|---|---|
| Humidity Range | 20-80% RH | 0-100% RH |
| Operating Voltage | 3.3V-5.5V | 3.3V-5.5V |
| Temperature range | 0°C to 50°C ±2°C | -40°C to 80°C ±0.5°C |
| Sampling rate (samples per second (SPS) or Hz) | 1 SPS (1 reading/sec) | 0.5 SPS (0.5 reading every 1 sec. or 2 sec/reading) |
| Note: DHT22 sensors gives more accurate readings but are slower compared to DHT 11 sensor (SPS is half) |
General Working:
a. Humidity Sensing Component:
The moisture holding substrate is sensitive to moisture/humidity. When the substrate absorbs water vapors, it releases ions that increase the conductivity between the electrodes. This change in resistance is measured and processed by the IC, and thus gives the corresponding OP.
b. Temperature Sensing Component:
The above image is of a thermistor, i.e. it changes the resistor with respect to the temperature. It has -ve temperature coefficient as, R∝ 1/T.
Circuit Connections:
| DHT11 | Arduino UNO |
|---|---|
| Operating voltage | 5v |
| DATA (Digital OP )/Signal (S) | Digital Pin 7 |
| GND | GND |
Actual Connections:
References:
Task 8 - BLDC Motor And Hall Effect Sensor
Objective:
Measure the speed of a BLDC motor using a hall effect sensor and display it on the serial monitor.
Learning:
The hall effect is a relationship between electric and magnetic fields through a semiconductor that allows electricity to flow when a magnetic field is applied within the vicinity of a given hall sensor.
Circuit Connections:
| A3114 | Arduino UNO |
|---|---|
| GND | GND |
| Vcc | 3.3v |
| Data | 2 |
| BLDC Motor | Arduino UNO |
| GND | GND |
| Vcc | 5v |
Actual Connections:
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References:
To continue reading my report (Task 10-17) click here