Week 7 - Journal

Circuit design:

• Link for circuit: Here

• On Tinkercad, I started to put the components I will use in my circuit.

• I put the Arduino board and breadboard.

• Mainly, the circuit consists of two action components (OUTPUT) which are the LCD screen and the buzzer, so I added them.

• Three inputs are used. An IR sensor is added as an input signal for the circuit, a potentiometer, and a push button (INPUT).

• I used 5v from arduino to power the circuit.

• I connected 5V and GND in arduino with +ve and -ve rails on the breadboard.

• I connected the buzzer on analog output pin 11 with +ve terminal and GND with -ve terminal.

• Then, I connected the LCD screen after reviewing the pinout from midweek tutorials. It is connected with arduino using 4 pins, VCC, GND, SDA and SCL. I connectd them to A4 & A5.

• The IR sensor is connected on pin 4 and +ve and -ve with rails to arduino power.

• The potentiometer is connected to analog input pin A3 to select the interval which the timer will work for.

• The push button is connected on pin 3 to start the timer and the other terminal to GND.

Code & logic:

• I started first by dividing the problem and defining the objectives clearly and what I want to achieve.

• As I want to make the push button trigger an action every time it is pressed and not only when holded down, I searched how to do so and I found several ways but the state change detection example was the easiest one to edit.

• It is simply done by using two variables, current button state and previous button state. The current one stores the readings from the button pin and at the end of the void loop the value is stored in the previous button state variable.

• By comparing the values of these variables, I can simply detect the current state of the button if it is pressed or not.

• I thought what is the right condition I should write and decided to make it like the following: If (btnState is HIGH and prevBtnState is LOW) => triggers the motors motion.

• This means when the button is pressed and before that it wasn't pressed. This technique is used mainly to prevent the repetition of the action while the button is held down.

• To use the LCD, I imported the <LiquidCrystal_I2c.h> library and edited the size to be 16x2 like the one I have.

• I declared a variable for component's pin. Two Variables to use with millis() function (current and previous millis) and two variables which are used as flags to control flow.

• In setup function, I wrote the pinMode for every component and initialized the lcd and printed "place the bottole" as the first thing to appear because placing bottle is what will initiate program flow.

• In the void loop() function, I declared 3 dynamic variables to store input componenets readings. Two digital inputs which are "irReading" (for IR sensor) and "btnState" (for push button)  and one analog input which is "interval" that is used to store potentiometer input.

• I used the map fucntion to scale the input values (0, 1023) to time interval from 5 sec to 30 sec. After that I divided it to ranges and each range corresponds to a letter . "S" for short, "M" for medium and "L" for long using an if-else.

•   For the timer, I used the function millis() which is a function that returns the number of milliseconds since the start of the program and this happens every iteration to keep track of current time like a clock.

• The program starts to operate when IR sensor reads LOW which means it detects a bottle and if so, it asks the user the adjust potentiometer to choose interval [S/M/L - printed top right on LCD] and press the button to start .

• This happens when timer is not active and reminder is not active. That means when timer hasn't been started and reminder hasn't been triggered.

• When button is clicked, the startTimer() function is called. This funciton simply does 3 things:

1. Prints "timer is running"

2. Set timerActive flag to true

3. Save a time stamp in prevMillis to indicate when timer started.

• This is the key point in using millis() logic, because later on, the difference between current and previous indicates if some period of time has passed.