Week 9
In this week's class we focused on input devices, which are components for interfacing embedded systems with the physical world. These could be buttons, motion detectors, temperature sensors, photoresistors or other sensors that can translate physical actions into digital signals.
Not to be confused with output devices like motors, displays, speakers, or LEDs, which we will see soon ;)* Spoiler: next week .
Types of Sensors
- Analog Sensors: Produce a continuous signal proportional to the measured parameter.
e.g.:
Phototransistors - Detect light intensity.
Load Cells - Measure weight or force.
Temperature Sensors - Such as thermistors, which detect temperature changes.
- Digital Sensors: Provide discrete signals, often in binary form.
e.g.:
Keypads - Detect specific key presses.
Touch Sensors - Identify touch or proximity.
Infrared Sensors - Detect obstacles or motion.
When selecting a sensor for a project, several factors must be considered. These include range and sensitivity, which determine the span of measurement and the smallest detectable change, as well as accuracy and precision, which refer to how close measurements are to the actual value and their consistency. Response time is another important characteristic, as it defines how quickly the sensor reacts to changes.
we discussed interfacing requirements, which depend on whether the sensor outputs analog or digital signals and whether additional components like amplifiers or signal conditioners are needed.
Interfacing sensors with microcontrollers requires understanding how they transmit data. Analog sensors connect to analog-to-digital converter (ADC) pins, which allow microcontrollers to read varying voltage levels. For instance, a phototransistor can be connected to an ADC pin to measure light intensity. Digital sensors, on the other hand, connect to digital input pins and often use communication protocols such as I²C, SPI, or UART. A keypad, for example, can be connected to digital inputs to detect key presses and respond accordingly.
Interfacing Sensors with Microcontrollers
Interfacing requirements depend on whether the sensor outputs analog or digital signals and whether additional components like amplifiers or signal conditioners are needed.
Analog sensors connect to analog-to-digital converter (ADC) pins, which allow microcontrollers to read varying voltage levels. For instance, a phototransistor can be connected to an ADC pin to measure light intensity.
Digital sensors, on the other hand, connect to digital input pins and often use communication protocols such as I²C, SPI, or UART. A keypad, for example, can be connected to digital inputs to detect key presses and respond accordingly.
Trying Out Sensors at the Lab
Hands on! So we tried using a variable resistors which are electronic components that allow you to adjust the resistance in a circuit, manually or automatically. Unlike fixed resistors, which have a constant resistance value, variable resistors can change their resistance to control voltage, current, or signal levels in an electrical circuit.
We chose a potenciometer and made a little circuit to give us a voltage reading.
void setup() {
// put your setup code here, to run once:
pinMode(17, INPUT);
Serial.begin(115200);
}
void loop() {
// put your main code here, to run repeatedly:
int lecture = analogRead(17);
Serial.println(lecture);
delay(50);
}
The potentiometer works as a voltage divider, varying its resistance in series with another resistor to change the output voltage sent to the pin.
Playing around with the potentiometer and turning the knob gives us a variable volage input. 4095V associated with the 3.3V output from our barduino board.
Then we tried a KY035 Hall Magnetic sensor to see how it is affected by a metal bolt.
We coded this to observe the variable voltage response as we moved it closer and further away from the sensor.
int sensorPin = 17; // interface pin with magnetic sensor
int val; // variable to store read values
void setup() {
pinMode(17, INPUT); // set analog pin as input
Serial.begin(115200); // initialize serial interface
}
void loop() {
val = analogRead(sensorPin); // read sensor value
Serial.println(val); // print value to serial
delay(100);
}
The standing voltage was half of 4095 value corresponding to 3.3V. The voltage drops or increases depending on the polarity.
We tried yet another more sensor, this time the KY027, also known as the Magic Light Cup Effect.
By using PWN* Pulse Width Modulation to control the LEDs on each module, we can create the illusion of light being "magically" transferred from one module to another when tilted—similar to pouring water between two cups, which inspired the name.
In the Arduino sketch, we used both modules to achieve this effect. Each module contains a mercury switch, which provides a digital signal used to regulate LED brightness via PWM.
int ledPinA = 15;
int switchPinA = 13;
int switchStateA = 0;
int ledPinB = 8;
int switchPinB = 10;
int switchStateB = 0;
int brightness = 0;
void setup()
{
pinMode(ledPinA, OUTPUT);
pinMode(ledPinB, OUTPUT);
pinMode(switchPinA, INPUT);
pinMode(switchPinB, INPUT);
}
void loop()
{
switchStateA = digitalRead(switchPinA);
if (switchStateA == HIGH && brightness != 255)
{
brightness ++;
}
switchStateB = digitalRead(switchPinB);
if (switchStateB == HIGH && brightness != 0)
{
brightness --;
}
analogWrite(ledPinA, brightness); // A slow fade out
analogWrite(ledPinB, 255 - brightness); // B slow bright up
delay(20);
}
We connected two KY027 modules to our Barduino on separate sides of a breadboard and adjusted the code to match our pin configuration.
To set up the effect, we pllace the modules so that their mercury switches face opposite directions. As you tilt them, the brightness of one module’s LED decreases while the other increases, giving the illusion that light is flowing between them.
Fun!
꩜꩜꩜ Input Devices on my Personal Board ꩜꩜꩜
Remember last week's board? Good. We are using it again to include a button as an input.
The switch I chose has a momentary action ( SPST* Single Pole Single Throw , normally open), operates with a maximum voltage of 12V DC, and supports a current of up to 50mA.
To program the board I need to get a hold a UPDI. Since I'm using the Attiny 412, I'll be using the toolchain described in Week 4.
These are how my connections look like.
