Week 9 Group Assignments -

Group assignment:

Probe an input device(s)’s analog levels and digital signals

Document your work on the group work page and reflect on your individual page what you learned

Probing Input Devices

We chose to probe 3 different types of input devices, a digital, analog and I2C. For all probing we used the PCB that Jeremy made in Week 8 look at the inputs.

Board used for probing.

Digital

For the digital input device we chose a button as it is quite common in many devices.

Setup

There is a button on Jeremy’s board connected to D6 so there was nothing to wire up. To probe the device, we used an aligator clip with a female header and plugged the female header onto one of the ground pins on the board. Then we soldered a jumper wire to the top of the XIAO onto pin 6. Then we used the alligator clips on the oscilliscope to connect to the jumpers.

Setup for digital measurement.

Closeup of the solder joint.

Code

We pushed button read code onto the board so that the D6 would be reading the pin.

int pushButton = 21;    // D6 on the board
int led= 20;

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);

  // make the pushbutton's pin an input:
  pinMode(pushButton, INPUT);
  pinMode(led, OUTPUT);

for (int i =0; i<=2; i++){
  digitalWrite (led, HIGH);
  delay (500);
  digitalWrite (led, LOW);
  delay (500);
}

digitalWrite (led, LOW);
}

void loop() {
  // read the input pin:
  int buttonState = digitalRead(pushButton);
  // print out the state of the button:
  Serial.println(buttonState);
  if (buttonState== 1){
    digitalWrite (led, HIGH);
  }
  else{ 
    digitalWrite (led, LOW);
      }

  delay(10);        // delay in between reads for stability
}

Results

Digital signals are a step input from 0 to input voltage and that is what we saw on the scope. The signal was 0 volts until the button was pushed when it jumped up to 3.3V.

Oscope output from button pushes.

Analog

For the analog probing, we chose a joystick with potentiometers. This is an easy way to create a variable analog output that can be read by the XIAO.

Setup

The initial thought was to plug the potentiometer into one of the analog inputs on Jeremy’s board. However, there were some issues on the board that provented us from doing this as the pad on A0 ripped off of the board. We also struggled with getting a good signal on A1. So, we flipped the board over and plugged the joystick to 3.3V, GND, and A1. Then we soldered the jumper to A1 on the top of the board.

Issues on the bottom of the board that prevented just plugging it in.

Analog read setup.

Code

We pushed this analaog read code to the XIAO so we could get readings.

int sensorPin = 2;    // select the input pin for the potentiometer
int sensorPin2 = 3; 
int ledPin = 20;      // select the pin for the LED
int sensorValueA0 = 0;  // variable to store the value coming from the sensor
int sensorValueA1 = 0; 


void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(ledPin, OUTPUT);
  pinMode (sensorPin, INPUT);
  pinMode (sensorPin2, INPUT);

  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
}

void loop() {
  // read the value from the sensor:
  sensorValueA0 = analogRead(sensorPin);
  sensorValueA1 = analogRead(sensorPin2);
  Serial.print("A0= ");
  Serial.print(sensorValueA0);
  Serial.print("     A1= ");
  Serial.println(sensorValueA1);

  delay(500);
}

Results

Analog signals are continuously variable between 0 and input voltage, in this case 3.3V. As we moved the joystick, we could see the wavy signal that corresponded to the position of the joystick as expected.

Analog data stream showing the continuously variable output.

I2C

For the I2C we chose the AHT20 temperature and humidity sensor. This sensor is easy to hookup and common for environmental monitoring.

Setup

We plugged the sensor into the I2C port on Jeremy’s board. We then used our aligator clip with female header connectors and put on a ground pin and one on the data pin of the I2C. Jeremy had 2 I2C connections on his board, so we used the data pin from the unused header.

Connecting the I2C with alligator clip jumpers.

Code

The following code was uploade to the XIAO to read the sensor.

#include <Adafruit_AHTX0.h>

Adafruit_AHTX0 aht;

void setup() {
  Serial.begin(115200);
  Serial.println("Adafruit AHT10/AHT20 demo!");

  if (! aht.begin()) {
    Serial.println("Could not find AHT? Check wiring");
    while (1) delay(10);
  }
  Serial.println("AHT10 or AHT20 found");
}

void loop() {
  sensors_event_t humidity, temp;
  aht.getEvent(&humidity, &temp);// populate temp and humidity objects with fresh data
  Serial.print("Temperature: "); Serial.print(temp.temperature); Serial.println(" degrees C");
  Serial.print("Humidity: "); Serial.print(humidity.relative_humidity); Serial.println("% rH");

  delay(500);
}

Results

Once hooked up to the scope, we could see a series of pulses every half second as the XIAO read the sensor. The pulses correspond to temperature and humidity data that the XIAO can untangle and turn into numerical values in the code.

I2C data traces from the AHT20.