ARDUINO: HYGROMETER FOR SENSING SOIL MOISTURE - Layout for this exercise:
- The goal of this exercise is to build an Arduino circuit able to detect moisture levels, for instance it could be used for a pot of plants. - The circuit will trigger a couple of alarms (buzzer sound and red LED) whenever the moisture level is under a moisture threshold specified at the Arduino sketch. - There are several moisture sensor available in the market, for instance the HL-69, YL-69, FC-28, ..., all of them compatible with the Arduino board. - A moisture sensor consists of two parts: a prong sensor and a controller. - On one side the controller is directly connected to the sensor, on the other side it is connected to the Arduino board:
AO (Analog Output) -> A0
DO (Digital Output) -> not used
GND (Ground) -> GND
VCC -> +5 V
- Code:
- Let's analyze the code. - First of all, the readings are taken from the analog A0 pin connected to the controller: - Because the range of digital conversion at the analog input A0 is from 0 to 1023, let's calibrate the reading so that 0 corresponds to 100% and 1023 to 0% of moisture: - When moisture is below 20% the two alarms are triggered: a buzzer produces a sound of 2000 Hz and a red LED blinks:
- Also, the serial ouput prints the moisture level on the screen every 2 seconds, whenever a new reading is made. In this picture the % of moisture varies abruptly when the sensor detects water:
- Testing the circuit, when the sensor is touching dry soil the buzzer beeps and the red LED blinks. However, if water is added to the soil both the beep and red light stop. Also, a message is printed through the serial monitor displaying the increase in humidity level:
- Layout for this exercise: 1 - Introduction - The goal of this exercise is to trigger 3 alarms when a temperature threshold is exceeded. - For that purpose an Arduino microcontroller is connected to 4 electronic devices: a) TMP36: precision temperature sensor that measures the temperature of the environment b) red LED: blinks when the temperature goes above a limit c) serial monitor: prints messages on the serial terminal d) buzzer or piezo element: beeps when the temperature goes above a limit 2 - Code - This is the code used in this exercise: 3 - Analysis of the code - The temperature sensor is connected to the input analog A0 pin which converts the voltage output of the sensor to digital values, and finally translating into Farenheit degrees:
- Setting a temperature threshold, three events happen if the threshold is exceeded: a) a beep of 2000 Hz and 500 ms:
b) a red LED blinks:
c) a warning message is printed at the serial monitor:
- The serial monitor is initialized to 9600 bauds: - The series of Farenheit temperatures is normally displayed at the monitor, until a warning message (WARNING, VERY HOT !!) is triggered when the temperature goes above 100.00 F:
4 - Testing the circuit - In this video it can be checked how the 3 alarms (red LED, buzzer beep and monitor message) go off when a hot air jet from a hair dryer is blown over the circuit, increasing the temperature above 100 F:
ARDUINO: PIEZOELECTRIC BUZZER PLAYING JINGLE BELLS 1 - Introduction - A buzzer is an electromechanical component that can be used to make noise or even play music. - Inside the buzzer there is a coil of wire and a small magnet. When current flows through the coil it becomes magnetized and pulls towards the magnet creating a tiny "click". When the click is played thousands of times per second tones are created. - The Arduino has a built-in command called tone() which clicks the buzzer at a certain frequency. - Frequencies used in this exercise and their corresponding notes: x (g for a lower octave) = 196 Hz y (a for a lower octave) = 220 Hz c = 261 Hz d = 293 Hz e = 329 Hz f = 349 Hz g = 392 Hz a = 440 Hz 2 - Layout schematics - The buzzer has two pins, one positive (marked by a "+" symbol) and the other negative. - In this example the positive pin is connected to Arduino digital pin 9 (optionally through a resistor of 330 Ohms), and the negative pin is connected to GND.
3 - Running the Arduino sketch - The code used in this Arduino sketch:
- Running the code over the circuit (the resistor of the previous schematics has been removed to obtain louder sound from the buzzer):
ARDUINO: SERVO AND DC SPINNING MOTORS 1 - Servomotor - Layout for this exercise: - The goal of this exercise is to make rotate a servo motor back and forth through the full range of motion, what is 180 degrees. - A servo motor include feedback circuitry that allows it to be commanded to specific positions, what makes it very useful in robotics. - The servo has got 3 wires that can be connected with jumper wires: black goes to ground, red goes to 5 V and yellow goes to the Arduino 6 digital pin.
- Code: - Let's analysis the code. - First of all the servo library is included, so that all servo functions can be easily accessed. Also, a servo object called "s" is defined: - Now, the servo object is attached to the Arduino 6 digital pin: - The movement goes from 0 to 180 degrees: - The first rotation takes 100 ms delay between each move, stepping 1 degree: - 1 second of delay between the two rotations: - The second rotation is faster because there is just 20 milliseconds between each move: - Testing the circuit:
2 - DC Spinning Motor - Layout for this exercise:
- The goal of this exercise is to connect a DC motor to an Arduino circuit so that the motor starts spinning and accelerating up to a maximum speed and then decelerates until stopping. - Two electronic components are used: a) Transistor: it helps to run the DC motor, because the motor needs more current (even 100 or 250 mA) than provided by the Arduino pins (40 mA). The transistor has 3 pins (Collector: connected to the motor, Base: connected to the resistor, Emitter: connected to GND). b) Diode: when the motor is spinning and suddenly turned off, the magnetic field inside it collapses, generating a voltage spike that can damage the transistor. To prevent this, a diode is used, diverting the voltage spike away from the transistor. The diode has 2 pins (Cathode: connected to 5 V, Anode: connected to the transistor) - Code: - Let's analyse the code. - The 10 pin is assigned as the motorPin and oputput mode. Also, the serial monitor is initialized with 9600 bauds, inviting the user to enter a speed inside the 0 to 255 interval:
- The analogWrite() function pulses the motorPin using the PWM(Pulse Width Modulation) technique, varying the width of the pulse from 0% to 100%. - The motor accelerates with 10 milliseconds delay between each move: - Same thing for the decelerating process: - Once uploaded the sketch to the board the user enters the rotation speed through the serial monitor interface:
- Testing the circuit:
