Nuts and Volts - November 2014

(go to the article link to find files for all of the different code listings):

❏ You should get results that appear somewhat like those in Figure 10.

// A101_ch10_light_sensor_voltage 7/2/14
// Joe Pardue
 
int sensorPin = A0; // analog input pin
int sensorValue = 0;  // store the analog input

Lab 2: Converting ADC Sensor Readings to Temperature

void setup() {
  Serial.begin(57600);
  Serial.println(“Measure light sensor voltage
  rev 1.0”);
}

Converting Arduino ADC readings to voltage and then converting those voltages to temperature readings is somewhat complicated. To reinforce our earlier discussion, we will write a program to create a series of fake ADC readings and verify that the techniques we discussed work as described.

void loop() {
 
  if(Serial.available())
  {
 char c = Serial.read();
 if(c == ‘r’)
 {
 // read the value from the sensor:
 sensorValue = analogRead(sensorPin);

Parts required: 1 Arduino

1 USB cable

Estimated time for this lab: 30 minutes

Serial.print(“LDR voltage: “);
Serial.print(sensorValue);
Serial.print(“  Voltage: “);

Check off when complete:

❏ Load the following program into the Arduino IDE:

Serial.println(((5.0*(float)sensorValue)/1024.0),
3);
 }
  }
}
 // A101_ch10_volts_to_temperature_test 8/14/14

❏ Notice that this program is identical to the

#define VOLTS_PER_ADC_STEP 5.0/1024.0
#define VOLTS_PER_DEGREE 0.01
#define temp_BASE -40.0
#define LOW_ADC 20.49
#define HIGH_ADC 358.61
#define LOW_VOLTAGE 0.5

A101_ch7_pot_voltage.ino program from Chapter 7, except that some comments are changed. This powerfully illustrates the value of code reuse.

❏ Load the program onto your Arduino and then run the Arduino serial monitor.

❏ Repeat the earlier experiment where you cover the sensor with your hand and then move it roughly two inches up for each subsequent measurement.

int tempSensorPin = A0; // analog input pin
float tempSensorADC = 0.0; // variable to for
 // the ADC reading
float tempertureSensorVoltage = 0.0;
 // variable for the converted voltage
float tempSensorVoltage = 0.0;
 // variable for the sensor voltage
float tempCelsius = 0.0;
 // variable for degrees Celsius