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Functionality

0 Input can be retrieved onto the Arduino in a number of ways both digital and analogue.

0 Sensors convert changes in a physical quantity to electrical signals that can be interpreted with the Arduino.

0 Temp sensors, Light Sensors, Force sensors are e.g..

Temperature sensors

0 Gives a Vout propotional to ambient room temperature.

0 Concept : as temperature increases, voltage across a p-n junction increases at a known rate. (in this case Vbe)

0 Voltage at Anlg.Pin in Volts = (reading from ADC) * (5/1024) V

0 Centigrade temperature = [(analog voltage in V) – 0.5] * 100

Before: Writing the code

0 Review:

0 How does the lm35 work?

0 Read datasheet of lm35.

0 How to connect it to arduino?

0 What reference to use?

0 What sort of noises will be present?

0 What does the analogue input signify?

Datasheet of LM35

Circuit connection diagram

Temp sensor code

0 Connect lm35 as per circuit diagram in 7. Temp Sensor folder.

0 We’re giving AREF as 3.3V to reduce noise from the LM35 and give more accurate readings.

0 Upload code onto Arduino and Output is seen in the Serial monitor of the Arduino.

Write the code

1. Decide which analogue pin you’re going to and assign it to a global variable

2. in setup() { }, initialize serial port to 9600 baud rate to send temp reading out to PC.

3. In loop() { }, take the analogue reading from a pin and store it in a temp float variable.

4. Multiply reading by 5.0 and then divide by 1024 to get voltage value read by the port. Store this is a float variable called volt.

5. Print out this value to the serial port and check.

Keep Writing the code

0 To get temp in centigrade, (volt – 0.5) * 100

0 This is the ambient temperature recognized by the LM35 in Celsius.

0 Send it to the serial port and check your code.

0 To convert to fahrenheight, mult by 9 then divide by 5 then add 32 to that result. Send it to serial port too.

0 Congratulate yourself please.

Improvements?

0 Use 3.3V as reference to increase resolution since datasheet says that resolution of lm35 ~ 10mV.

0 Put in on PCB to avoid noise by breadboard internal resistance,

0 DO NOT LIGHT THE LM35 OR IMMERSE IT IN WATER.

0 Make a waterproof casing for the lm35 to test temp of liquids.

0 Any other applications?

LDR

0 An LDR is a Light Dependent Resistor.

0 As in the resistance offered by this device to an electrical circuit is dependent on the amount of light falling on the circuit.

0 Also called photocells because they convert light energy to an electrical response.

0 Useful for on-when-light/off-when-dark.

How to connect the LDR

0 LDR is basically a resistor, so it can be connected anyway.

0 You need a pull-down resistor to avoid sinking all the current onto the arduino pin.

0 Circuit is GND-10kohn-LDR-VCC.

0 This circuit will only work if between 0-5V. If light is too bright, it will saturate at 5V.

0 putting a variable resistor in place of 10k allows for controlling saturation with too bright/too dark light.

Ambient light like…

Ambient light (lux)

Photocell resistance (Ω)

LDR + R (Ω)

Current thru LDR +R

Voltage across R

Dim hallway

0.1 lux 600KΩ 610 KΩ 0.008 mA 0.1 V

Moonlit night

1 lux 70 KΩ 80 KΩ 0.07 mA 0.6 V

Room 10 lux 10 KΩ 20 KΩ 0.25 mA 2.5 V

Dark overcast day / Bright room

100 lux 1.5 KΩ 11.5 KΩ 0.43 mA 4.3 V

Overcast day

1000 lux 300 Ω 10.03 KΩ 0.5 mA 5V

Writing code!

0 decide analoge pin used as input to LDR.

0 In setup(){ }, initialize serial port with 9600.

0 In loop(){ }, first do an analogueread(pin) and store it in an int variable called reading.

0 This value represents illumination received by LDR. 0 Send it to Serial Port.

0 Allow delay of some time to let the ADC settle.

Application 1

0 Make thresholds and determine the brightness received and send it via serial port.

if (reading < 10) { Serial.println(" - Dark"); } else if (reading < 200) { Serial.println(" - Dim"); } else if (reading < 500) { Serial.println(" - Light"); } else if (reading < 800) { Serial.println(" - Bright"); } else { Serial.println(" - Very bright"); }

Application 2

0 Take the analogue reading and use it as the delay amount in an LED blinking scenario. Use ledpin = 13.

void loop() { val = analogRead(LDR); digitalWrite(ledPin, HIGH); delay(val); digitalWrite(ledPin, LOW); delay(val); }

Another Application

0 Put three LEDs around the LDR. Red, Green and Blue.

0 Put an object of a particular color in front of the LDR.

0 Light up RED LED and measure LDR value

0 Light up GREEN LED and measure LDR value

0 Light up BLUE LED and measure LDR value

0 From these three analogue values you can determine the color of object being sensed.

Sensor Data on PC

0 Reading and plotting sensor data on PC is very simple on the arduino.

0 Send data continuously to the computer over the serial port.

0 Data can be viewed by any program capable of viewing this data

Send sensor data to serial port

0 Open the folder Sensor data graph

0 Upload the arduino code onto the arduino and close arduino IDE after checking serial monitor.

0 In softwares folder extract the processing folder.

0 Open processing and copy the processing code onto it and run.

0 Make sure serial port number in the processing sketch matches arduino