EP1000

Input Devices

Input devices are often called Sensors. Output devices are often called Actuators. The process of connecting a Sensor or Actuator to a computer processor system is called Interfacing.

Sensors

• A sensor is a device, module, machine or subsystem whose purpose is to detect events or changes in its environment and send the information to other electronics, frequently a computer processor. (Ref: Wikipedia: Sensor)
• Used in everyday objects to read changes in the environment.
• Sensor readings are usually analog by nature.
• Changes are usually slower in availability (compared to computer processors) and require some processing techniques.

Methods of reading sensors

• There are 3 basic methods of reading/obtaining information from a sensor. These methods are dependent upon the availability of the information, as read by the sensor
  • Always available
    • Just read the data, data is always available
    • Changes to the reading occur very slowly.
    • E.g. temperature
  • Polling
    • Processor has to continually query/poll the sensor for information.
    • Sensor will usually indicate whether there is new information through another signal or have a drastic change in the reading to indicate that there is a new reading available.
    • When Processor “sees” this change, data is read.
    • E.g. switch
  • Triggering
    • A trigger is a signal(s) that is used to initiate the reading.
    • Sequence is as follows:
      • Processor sends a signal to the sensor for data
      • Sensor gathers information, and when ready
      • Sends reading back to the Processor. The Sensor may also indicate that data is ready to be read by sending back an Acknowledge/Ready signal
    • E.g. Ultrasonic distance measurement
• Sensor data
  • Real environment data is analog by nature. It may be some physical element e.g. temperature, distance
  • A sensor converts this data into an equivalent electrical signal/voltage that is sent to the computer processor.
  • The computer processor has to read this electrical signal and convert it into an understandable value.
  • Analog signals
    • most common type of sensor data
    • requires conversion to a digital value, usually with an ADC
    • usually it is a direct relationship e.g. V = K * environment-value
  • Digital signals
    • these sensors are configured as smart devices, with processing power
    • sensor itself converts the analog values into a digital signal (e.g. pulse or series of digits)
    • processor needs to decode to understand the value
• Arduino Libraries
  • The Arduino System is very popular because there is large number of libraries (of code) available for almost every Sensor that you can think of.
  • Add libraries to the Arduino IDE System (Ref: Arduino.cc Installing Additional Arduino Libraries)
    • There are two types of libraries,
      • Search able using the Arduino IDE system (Internal)
      • External libraries, available as compressed C++ code.
    • How to add a library using the Library Manager
      1. IDE > Sketch > Install Library > Manage Libraries
      2. Search for the library
      3. Highlight and click Install, when complete, it should state “Installed”
    • How to add an External library (.ZIP format)
      1. Search for the library on the Internet
      2. Download the library, usually in a compressed .ZIP file
      3. IDE > Sketch > Include Library > Add .Zip Library
      4. Close the IDE. Re-open.
    • How to manually add an External Library
      1. Search for the library on the Internet
      2. Download the library, usually in a compressed .ZIP file
      3. Locate where your sketch folder is found on your computer using IDE > File > Preferences > Sketchbook
      4. Extract the Library from the ZIP file (this is usually a folder)
      5. Copy the extracted library folder to [Sketchbook folder] > Libraries folder
      6. Close the IDE. Re-open.
  • Check that the Library has been added using IDE > Sketch > Include Library. You should see your installed library there.
  • To apply the library code to your application, add the header file a the top of your sketch using IDE > Sketch > Include Library > LibName. The header file has an extension of .h.

Types of Sensors

• Switches
  • An electrical component that can disconnect or connect the conducting path of a circuit.
  • Provides a LOW or HIGH signal depending on the circuitry.
  • Use digitalRead() to determine value of a switch.
  • Be aware of debouncing techniques when mechanical switches are in use.
  • Types of switches
    • Toggle
      • a mechanical switch that changes the state each time the switch is thrown/manipulated.
      • e.g. If in the ON position, throwing the switch will change it to an OFF position.
      • the state remains until the switch is thrown
    • Pushbutton switch
      • a spring-loaded mechanical switch that changes state when the switch is pressed. When released (and because of the spring) the switch returns to the original state.
      • Two types of pushbutton switches
        • normally closed - push to open/break connection
        • normally open - push to close/make connection
    • Slide switch
      • a switch which is closed or opened by a sliding mechanism.
      • when changed, the switch remains in the new state.
    • Touch Capacitative switch
      • switch works based on body capacitance.
      • when a person touches it, the body increases the capacitance of the switch and triggers the switch  
• Temperature, Humidity
  • the environment can be measured using a number of devices, the most common and cheapest is to use the DHT-11 temperature and humidity sensor.
    • temperature is a physical quantity that expresses hot or cold.
    • reference temperatures
      • freezing point of water = 0 degrees Centigrade
      • boiling point of water = 100 degrees Centigrade
      • typical Singapore temperature = 28 - 32 degrees Centigrade
  • humidity is the measure of the concentration of water vapor present in the air. Singapore’s humidity is between 70-90%.
  • the following devices can be used with the Arduino system
    • DHT-11
      • operating voltage range 3.5~5.5V
      • temperature range 0-50C, humidity 20-90%
      • resolution 16-bit
      • accuracy +/- 1C, +/- 1%
    • DHT-22
      • temperature range -40~80C, humidity 0~100%
      • resolution 16-bit
      • accuracy +/- 0.5C, +/- 1%
    • LM35 temperature sensor
      • operating voltage range -2~35V, typical 5V
      • temperature range -55C ~ 150C
      • accuracy +/- 0.5C
    • DS18B20 temperature probe
      • operating voltage range 3V ~ 5V
      • temperature range -55C ~ 125C
      • accuracy +/- 0.5C
  • Interfacing to the Arduino Uno

  

  • Interfacing the DHT-11
    • requires the use of the DHT-11 library

 

• Distance
  • This depends on the distance to be measured. The devices can range from a limit switch to an ultrasonic sensor.
  • Photoelectric InfraRed Avoidance detection/Proximity sensor
    • distance: 2cm ~ 40cm
    • can use ENable pulse or continuous measurement
    • avoidance distance is adjusted with potentiometer
    • does not measure distance, just detects it
  • Ultrasonic HC-SR04
    • distance: 2cm ~ 4 m
    • uses SONAR, returns a pulse proportional to the distance
    • ranging accuracy 3mm, measuring angle 15 degrees
    • distance is equivalent to pulse measured

  

 

• Motion detection
  • Commonly used to detect the presence of humans or animals in a room/vicinity.
  • HC-SR501 PIR Sensor
    • PIR - Passive Infra Red Sensor
    • Detectable cover distance 120 degrees, 7 meters
    • has a repeatable and non-repeatable operating mode

  

  • Microwave module Doplar detection RCWL-0516
    • Stand-alone module using “Doplar Radar” to detect motion
    • Can be connected to a computer processor
    • Detectable cover distance 7 meters

 

• Light Measurement & Detection
  • Light intensity can be detected/measured using LDR (Light Dependent Resistors) or Light Sensor Modules (using Photo transistor circuits)
  • LDR 5516
    • Low cost measurement/detection of light using LDR
    • Variable analog voltage received as input\
    • Can be calibrated
    • Measured using Arduino analogRead() function
    • Use a 5K ~ 10K resistor for the Arduino Uno

  

  • Using a Photocell

 

• Time
  • These are modules that allow you to keep track of the time. A RTC uses a small battery, crystal and memory to maintain a on-going clock which can be read to provide the current date and time.
  • Real-time Clock Modules
    • RTC DS3231 using I2C
    • RTC DS1302 using single-wire

 

• Rotary Encoders
  • a rotary encoder reads the positional value of a shaft by comparing 2 pulses as the shaft turns.
  • looks like a potentiometer, but does not change resistance
  • rotary encoders are now used for volume controls, motor encoders etc
• Weight
  • A load cell provides a means of measuring the weight of an object. This is done by the measuring the contraction of metals. Usually a module is provided to read the data from a load cell and transfer the results to the computer processor.
  • Load Cell Weight Sensor HX711 AD Converter
• Water
  • Water level sensor

 

• Arduino Sensor Kit
  • 37 in 1 kit

 

Assignment 13 Interfacing a LDR with an RGB LED

In this assignment, you will attempt to interface an input analog device to your Arduino and produce equivalent output on a RGB LED.

«««< HEAD:input_devices/input_devices.md You can find the assignment here

 

Useful sites for Arduino Interfacing

Here are some of the more “reputable/trust-worthy” sites for Arduino modules

You can view the assignment here

d5ae412f2f86efb3fc30523253ebbd20ce1a1de9:input_devices/inputdevices.md

• Last Minute Engineers
• Dronebot Workshop
• Adafruit
• Instructables
• Arduino Project Hub

 

January 2021