9. Input Devices

The group assignment for this week was to probe input device(s)’s analog levels and digital signals.

1. Phototransistor

First we probed a phototransistor that was made by a previous student.

Connect the XIAO 3.3v to the anode of the phototransistor, the XIAO D0 pin to the cathode of the phototransistor, and connect the cathode of the phototransistor to the XIAO GND via a 10K ohm resistor.

Specs of the phototransistor:

Parameter	Value
Working voltage	30 V
Working Current	100nA - 20mA
xxx
Datasheet	PT15-21C/TR8

Workflow

Connect the clip to the wire on input device, and plug in the other cable to Ground.

Code

const int Sensor = 26; // analog input pin RP2040 pin 26 or XIAO pin A0 

void setup() 
{
  Serial.begin(115200);
  pinMode(Sensor, INPUT);
}

void loop() 
{
  // Read in the ADC and convert it to a voltage:
  int proximityADC = analogRead(Sensor);
  float proximityV = (float)proximityADC * 1000.0 / 1023.0;
  Serial.println(proximityV);
  delay(100);
}

Result
I found that making it darker made the waveform rise, and making it brighter made the waveform fall.

2. Slider LED object

Specs of the input device

Parameter	Value
Processor	Xiao RP2040
Working voltage	3.3V
Change Current	analog input
LED	RGB full color LED

Code

Input: analog value from each slider
Output: LED

/*
  Analog input, analog output
*/

// These constants won't change. They're used to give names to the pins used:
const int analogInPin1 = A0;  // Analog input pin that the potentiometer is attached to
const int analogInPin2 = A1;  // Analog input pin that the potentiometer is attached to
const int analogInPin3 = A2;  // Analog input pin that the potentiometer is attached to

const int OutPin1 = D10;  // Analog output pin that the LED is attached to
const int OutPin2 = D9;  // Analog output pin that the LED is attached to
const int OutPin3 = D8;  // Analog output pin that the LED is attached to

int digi_min = 0;       // Digital min value
int ana_min = 0;        // Analog min value
int digi_max = 255;     // Digital max value
int ana_max = 1023;     // Analog max value

// Initial value
int sensorValue1 = 0;  // value read from the pot
int outputValue1 = 0;  // value output to the PWM (analog out)
int sensorValue2 = 0;  // value read from the pot
int outputValue2 = 0;  // value output to the PWM (analog out)
int sensorValue3 = 0;  // value read from the pot
int outputValue3 = 0;  // value output to the PWM (analog out)

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}
void loop() {

  // read analog in value and return digital value  
  outputValue1 = ana_digi_Valchange(analogInPin1);
  outputValue2 = ana_digi_Valchange(analogInPin2);
  outputValue3 = ana_digi_Valchange(analogInPin3);

  // Set the pin
  pinMode(OutPin1,OUTPUT);
  pinMode(OutPin2,OUTPUT);
  pinMode(OutPin3,OUTPUT);

  // analog writing
  analogWrite(OutPin1,outputValue1);
  analogWrite(OutPin2,outputValue2);
  analogWrite(OutPin3,outputValue3);

   delay(500);
}

Result
We confirmed that the waveform was changing up and down along the slider.

3. Step response

Specs of the input device

“ESP32-S3 has 14 capacitive-sensing GPIOs, which detect variations induced by touching or approaching the GPIOs with a finger or other objects.” (ESP32-S3 datasheet)

Parameter	Value
Processor	Xiao ESP32-S3
Working voltage	3.3 V
Working Current	500-1500 mA
Change Current	analog input
Touch Sensor interface	GPIO1 ~ GPIO14
Datasheet	ESP32-S3 XIAO ESP32S3

Code

// ESP32 Touch Test

void setup() {
  Serial.begin(115200);
  delay(1000);  // give me time to bring up serial monitor
  Serial.println("ESP32 Touch Test");
}

void loop() {
  Serial.print(touchRead(T1));  // get value using T1
  Serial.print(",");
  Serial.print(touchRead(T2));  // get value using T2
  Serial.print(",");
  Serial.print(touchRead(T3));  // get value using T3
  Serial.print(",");
  Serial.print(touchRead(T7));  // get value using T7
  Serial.print(",");
  Serial.println(touchRead(T8));  // get value using T8
  delay(1000);
}

Result
We measured the response of the touch of two pins.

Useful links

Have you answered these questions?

• Documented what you learned from interfacing an input device(s) to your microcontroller and optionally, how the physical property relates to the measured results.