Jose Alegria - Fab Academy

Input Devices

Assignment

wHAT iS THE ASSIGNMENT ABOUT?

Measure something: add a sensor to a microcontroller board that you have designed and read it.

Group Assignment:

Probe an input devices analog and digital signals

1^st Step. Electronics design

I used the same board I designed for electronics design, with the modifications made for output devices:

- Removed the extra button and LED

- Added input and output pins to be able to connect and disconnect several peripherals to the board.

- Added 5 V, 3.3 V and GND pins to be able to send signals to peripherals.

If you wish to see more information for this board designs, please follow the links below:

Electronics Design

Output Devices

2^nd Step. Input Devices

For this assignment I will use an ultrasonic sensor to determine distance with my modified board. First, I had to search for the appropriate setting for this ultrasonic sensor:

The ultrasonic sensor has 4 terminals:

- +5 V pin

- Trigger

- Echo

- GND

This means that I am going to use the 5V connector of my modified board for the first time. Trigger and Echo are going to be connected to one of the free input output pins (I have the pins 4, 5, 8 and 9 free to do this). GND connector is the same I have been using since I designed this new board.

Finally, I connected the pins as follows:

- 5 V: to one of the extra 5V pins.

- GND: to Ground

- Trigger: to pin 4

- Echo: to pin 5

3^rd Step. Code and programming

To measure distance with this sensor we will have to calculate the difference between the emission of an ultrasonic beep and the reception of the sound and calculate how much time does the sound need to travel certain distance.

That gives us one math operation to do before publishing the distance: sound takes 294 microseconds to travel 10 cm, so to convert the number to cm we should divide the time by 29.4 and by 2 (to consider the distance going forth and back).

This is a simple operation that we will be making each time we take a measure.

After setting that here is the code:

const int trig = 4;

const int echo = 5;

void setup() {

Serial.begin(9600);

pinMode(trig, OUTPUT);

pinMode(echo, INPUT);

long cm;

long dur;

}

void loop() {

long duration, inches, cm;

digitalWrite(trig, LOW);

delayMicroseconds(2);

digitalWrite(trig, HIGH);

delayMicroseconds(10);

digitalWrite(trig, LOW);

dur = pulseIn(echo, HIGH);

cm = dur *10 / 294 / 2;

Serial.print(cm);

Serial.print("cm");

Serial.println();

delay(100);

}

3^rd Step. Operation

Until now, the only way we have to receive the distance information would be to open the serial monitor, I declared it during setup and sent the information during the operation.

To open the serial monitor you should use the Tools menu and select Serial Monitor

Once you have the monitor open, we can start testing the ultrasonic sensor.

Conclussions

Once we know how the microprocessor pins work is easy to plug and unplug the input device and changing the pin where it is in the code.

Original Files

1. Source code

Nueval Checklist

- Linked to the group assignment page.

- Documented what you learned from interfacing an input device to microcontroller and how the physical property relates to the measured results.

- Documented your design and fabrication process or linked to previous examples.

- Explained the programming processes you used.

- Explained problems and how you fixed them.

- Included original design files and source code.

- Included a hero shot or video of your board.

2022