When I posted the “LED Control Using DIP Switch” sketch last year (a simple setup the turned on the LED corresponding to that switch position), I also had a slightly modified version of it in which the DIP switch controlled six different light patterns on the LEDs (scroll right, left, in, out, back and forth and random). It presented a “cleaned-up” version of the code using for loops and compared it to the “long-hand” version, showing the trade-off between ease of understanding and conciseness. Except that… I forgot to post it.

Last week someone contacted me asking a question about a similar project he is working on and when I wanted to refer him to this modified sketch I realized it wasn’t on the blog. (Here’s the original sketch and schematic for reference).

What follows below is the missing blog post (not anymore), a comparison between the more readable sketch (easier for beginners to understand) and the more concise version, in a series of snippets showing the main differences between the two versions of the sketch.

The concise version generates a binary sketch that occupies approximately 25% less memory and is almost half as long in lines of code. The entire source code listings are at the very bottom of this post.

Note: the line above each snippet reflects the modification that shortened the sketch.

1) not using #define directives for the LED and switch pins on the Arduino in order to use for loops:

    } else {
     // default: off
     digitalWrite(LED1, LOW);
     digitalWrite(LED2, LOW);
     digitalWrite(LED3, LOW);
     digitalWrite(LED4, LOW);
     digitalWrite(LED5, LOW);
     digitalWrite(LED6, LOW);
   }

    } else {
     // default: off
     for (i = 13; i >= 8; i--) {
       digitalWrite(i, LOW);
     }

2) using a state variable array (and consequently a for loop) as opposed to individual state variables:

   s1state = digitalRead(S1);
   s2state = digitalRead(S2);
   s3state = digitalRead(S3);
   s4state = digitalRead(S4);
   s5state = digitalRead(S5);
   s6state = digitalRead(S6);

   for (i = 0, j = 7; i < 6, j >= 2; i++, j--) {
     state[i] = digitalRead(j);
   }

3) if (x) versus if (x == 1) (when x is either 0 or 1, then the (x == 1) expression can be written as simply (x)):

    } else if (s5state == 1) {
     // scroll back and forth

    } else if (state[4]) {
     // scroll back and forth

4) long, repetitive code to randomly turn on or not each LED (for a random duration up to 300 milliseconds) replaced with for loop:

    } else if (s6state == 1) {
     // random
     randomSeed(analogRead(3));
     onoroff = random(0, 2);
     millisecs = random(0, 301);
     digitalWrite(LED1, onoroff);
     delay(millisecs);
     randomSeed(analogRead(3));
     onoroff = random(0, 2);
     millisecs = random(0, 301);
     digitalWrite(LED2, onoroff);
     delay(millisecs);
     randomSeed(analogRead(3));
     onoroff = random(0, 2);
     millisecs = random(0, 301);
     digitalWrite(LED3, onoroff);
     delay(millisecs);
     randomSeed(analogRead(3));
     onoroff = random(0, 2);
     millisecs = random(0, 301);
     digitalWrite(LED4, onoroff);
     delay(millisecs);
     randomSeed(analogRead(3));
     onoroff = random(0, 2);
     millisecs = random(0, 301);
     digitalWrite(LED5, onoroff);
     delay(millisecs);
     randomSeed(analogRead(3));
     onoroff = random(0, 2);
     millisecs = random(0, 301);
     digitalWrite(LED6, onoroff);
     delay(millisecs);
   }

    } else if (state[5]) {
     // random
     for (i = 13; i >= 8; i--) {
       randomSeed(analogRead(i - 8));
       onoroff = random(0, 2);
       millisecs = random(0, 301);
       digitalWrite(i, onoroff);
       delay(millisecs);
     }
   }

Here’s the full long version:

• Binary sketch size: 3654 bytes
• Code size was sacrificed in order to improve readability for beginners
• Sketch length: 205 lines

  // www.TheElectronicsHobbyist.com/blog
  // Natalia Fargasch Norman
  // LED control via DIP switches

  // Arduino pins used for the LEDs
  #define LED1 13
  #define LED2 12
  #define LED3 11
  #define LED4 10
  #define LED5 9
  #define LED6 8

  // Arduino pins used for the switches
  #define S1 7
  #define S2 6
  #define S3 5
  #define S4 4
  #define S5 3
  #define S6 2

  // State of each switch (0 or 1)
  int s1state;
  int s2state;
  int s3state;
  int s4state;
  int s5state;
  int s6state;

  // Random values for LED state and delay
  long onoroff;
  long millisecs;

  void setup() {
    // pins for LEDs are outputs
    pinMode(LED1, OUTPUT);
    pinMode(LED2, OUTPUT);
    pinMode(LED3, OUTPUT);
    pinMode(LED4, OUTPUT);
    pinMode(LED5, OUTPUT);
    pinMode(LED6, OUTPUT);
    // pins for switches are inputs
    pinMode(S1, INPUT);
    pinMode(S2, INPUT);
    pinMode(S3, INPUT);
    pinMode(S4, INPUT);
    pinMode(S5, INPUT);
    pinMode(S6, INPUT);
  }

  void loop() {
    s1state = digitalRead(S1);
    s2state = digitalRead(S2);
    s3state = digitalRead(S3);
    s4state = digitalRead(S4);
    s5state = digitalRead(S5);
    s6state = digitalRead(S6);
    if (s1state == 1) {
      // scroll right
      digitalWrite(LED1, HIGH);
      delay(250);
      digitalWrite(LED1, LOW);
      digitalWrite(LED2, HIGH);
      delay(250);
      digitalWrite(LED2, LOW);
      digitalWrite(LED3, HIGH);
      delay(250);
      digitalWrite(LED3, LOW);
      digitalWrite(LED4, HIGH);
      delay(250);
      digitalWrite(LED4, LOW);
      digitalWrite(LED5, HIGH);
      delay(250);
      digitalWrite(LED5, LOW);
      digitalWrite(LED6, HIGH);
      delay(250);
      digitalWrite(LED6, LOW);
    } else if (s2state == 1) {
      // scroll left
      digitalWrite(LED6, HIGH);
      delay(250);
      digitalWrite(LED6, LOW);
      digitalWrite(LED5, HIGH);
      delay(250);
      digitalWrite(LED5, LOW);
      digitalWrite(LED4, HIGH);
      delay(250);
      digitalWrite(LED4, LOW);
      digitalWrite(LED3, HIGH);
      delay(250);
      digitalWrite(LED3, LOW);
      digitalWrite(LED2, HIGH);
      delay(250);
      digitalWrite(LED2, LOW);
      digitalWrite(LED1, HIGH);
      delay(250);
      digitalWrite(LED1, LOW);
    } else if (s3state == 1) {
      // scroll in
      digitalWrite(LED1, HIGH);
      digitalWrite(LED6, HIGH);
      delay(250);
      digitalWrite(LED1, LOW);
      digitalWrite(LED6, LOW);
      digitalWrite(LED2, HIGH);
      digitalWrite(LED5, HIGH);
      delay(250);
      digitalWrite(LED2, LOW);
      digitalWrite(LED5, LOW);
      digitalWrite(LED3, HIGH);
      digitalWrite(LED4, HIGH);
      delay(250);
      digitalWrite(LED3, LOW);
      digitalWrite(LED4, LOW);
    } else if (s4state == 1) {
      // scroll out
      digitalWrite(LED3, HIGH);
      digitalWrite(LED4, HIGH);
      delay(250);
      digitalWrite(LED3, LOW);
      digitalWrite(LED4, LOW);
      digitalWrite(LED2, HIGH);
      digitalWrite(LED5, HIGH);
      delay(250);
      digitalWrite(LED2, LOW);
      digitalWrite(LED5, LOW);
      digitalWrite(LED1, HIGH);
      digitalWrite(LED6, HIGH);
      delay(250);
      digitalWrite(LED1, LOW);
      digitalWrite(LED6, LOW);
    } else if (s5state == 1) {
      // scroll back and forth
      digitalWrite(LED1, HIGH);
      delay(250);
      digitalWrite(LED1, LOW);
      digitalWrite(LED2, HIGH);
      delay(250);
      digitalWrite(LED2, LOW);
      digitalWrite(LED3, HIGH);
      delay(250);
      digitalWrite(LED3, LOW);
      digitalWrite(LED4, HIGH);
      delay(250);
      digitalWrite(LED4, LOW);
      digitalWrite(LED5, HIGH);
      delay(250);
      digitalWrite(LED5, LOW);
      digitalWrite(LED6, HIGH);
      delay(250);
      digitalWrite(LED6, LOW);
      digitalWrite(LED5, HIGH);
      delay(250);
      digitalWrite(LED5, LOW);
      digitalWrite(LED4, HIGH);
      delay(250);
      digitalWrite(LED4, LOW);
      digitalWrite(LED3, HIGH);
      delay(250);
      digitalWrite(LED3, LOW);
      digitalWrite(LED2, HIGH);
      delay(250);
      digitalWrite(LED2, LOW);
    } else if (s6state == 1) {
      // random
      randomSeed(analogRead(3));
      onoroff = random(0, 2);
      millisecs = random(0, 301);
      digitalWrite(LED1, onoroff);
      delay(millisecs);
      randomSeed(analogRead(3));
      onoroff = random(0, 2);
      millisecs = random(0, 301);
      digitalWrite(LED2, onoroff);
      delay(millisecs);
      randomSeed(analogRead(3));
      onoroff = random(0, 2);
      millisecs = random(0, 301);
      digitalWrite(LED3, onoroff);
      delay(millisecs);
      randomSeed(analogRead(3));
      onoroff = random(0, 2);
      millisecs = random(0, 301);
      digitalWrite(LED4, onoroff);
      delay(millisecs);
      randomSeed(analogRead(3));
      onoroff = random(0, 2);
      millisecs = random(0, 301);
      digitalWrite(LED5, onoroff);
      delay(millisecs);
      randomSeed(analogRead(3));
      onoroff = random(0, 2);
      millisecs = random(0, 301);
      digitalWrite(LED6, onoroff);
      delay(millisecs);
    } else {
      // default: off
      digitalWrite(LED1, LOW);
      digitalWrite(LED2, LOW);
      digitalWrite(LED3, LOW);
      digitalWrite(LED4, LOW);
      digitalWrite(LED5, LOW);
      digitalWrite(LED6, LOW);
    }
  }

And here’s the full “cleaned-up” version:

• Binary sketch size: 2826 bytes
• Sketch length: 119 lines

  // www.TheElectronicsHobbyist.com/blog
  // Natalia Fargasch Norman
  // LED control via DIP switches

  // Arduino pins used for the LEDs
  // LED1 13
  // LED2 12
  // LED3 11
  // LED4 10
  // LED5 9
  // LED6 8

  // Arduino pins used for the switches
  // S1 7
  // S2 6
  // S3 5
  // S4 4
  // S5 3
  // S6 2

  // State of each switch (0 or 1)
  int state[6];

  // Random values for LED state and delay
  long onoroff;
  long millisecs;

  // loop counters
  int i, j;

  // delay
  int d = 250;

  void setup() {
    // pins for LEDs are outputs
    // LEDs 1-6 on pins 13-8
    for (i = 13; i >= 8; i--) {
      pinMode(i, OUTPUT);
    }
    // pins for switches are inputs
    // switches 1-6 on pins 7-2
    for (i = 7; i >= 2; i--) {
      pinMode(i, INPUT);
    }
  }

  void loop() {
    for (i = 0, j = 7; i < 6, j >= 2; i++, j--) {
      state[i] = digitalRead(j);
    }

    if (state[0]) {
      // scroll right
      for (i = 13; i >= 8; i--) {
        digitalWrite(i, HIGH);
        delay(d);
        digitalWrite(i, LOW);
      }

    } else if (state[1]) {
      // scroll left
      for (i = 8; i <= 13; i++) {
         digitalWrite(i, HIGH);
         delay(d);
         digitalWrite(i, LOW);
       }

   } else if (state[2]) {
       // scroll in
       // light up LEDs on pins i and 8+(13-i)
       for (i = 13; i >= 11; i--) {
        digitalWrite(i, HIGH);
        digitalWrite(21 - i, HIGH);
        delay(d);
        digitalWrite(i, LOW);
        digitalWrite(21 - i, LOW);
      }

    } else if (state[3]) {
      // scroll out
      // light up LEDs on pins i and 8+(13-i)
      for (i = 11; i <= 13; i++) {
         digitalWrite(i, HIGH);
         digitalWrite(21 - i, HIGH);
         delay(d);
         digitalWrite(i, LOW);
         digitalWrite(21 - i, LOW);
       }

    } else if (state[4]) {
       // scroll back and forth
       for (i = 13; i >= 8; i--) {
        digitalWrite(i, HIGH);
        delay(d);
        digitalWrite(i, LOW);
      }
      for (i = 9; i <= 12; i++) {
        digitalWrite(i, HIGH);
        delay(d);
        digitalWrite(i, LOW);
      }

    } else if (state[5]) {
       // random
       for (i = 13; i >= 8; i--) {
        randomSeed(analogRead(i - 8));
        onoroff = random(0, 2);
        millisecs = random(0, 301);
        digitalWrite(i, onoroff);
        delay(millisecs);
      }      

    } else {
      // default: off
      for (i = 13; i >= 8; i--) {
        digitalWrite(i, LOW);
      }
    }
  }

Check out the video of this sketch in action.

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2. Controlling a Seven-Segment Display Using Arduino Part 3
3. Arduino 2-Digit 7-Segment Display with Buttons | Part 4
4. Controlling a Seven-Segment Display Using Arduino Part 2

If you’ve read Getting Started with Arduino (click on link to read my review of the book) you must have noticed that the circuit on page 43 uses a 10K Ohm resistor in series with the pushbutton. (If you haven’t read it yet, the example in the schematic on the right is similar to the setup featured on the book).

Consider a microcontroller with a digital input pin connected to a switch. When the switch is closed, the pin is connected to GND. When the switch is open, the signal is not connected to anything and is left at an unknown state. The signal is in this case said to be “floating”. This is pictured in circuit (1).

To remedy this problem we pull the signal up to VCC, as shown in circuit (2). Now when the switch is open the signal is connected directly to VCC and is at a known state. But notice that when the switch is closed, VCC and GND are connected, creating a short.

To prevent the short we place a resistor between the input pin and VCC, as shown in circuit (3). This resistor is called a “pull up” resistor.

Pull down resistors work almost in the same way, except the circuit is connected so that when the switch is closed the input pin is connected to VCC, and when switch is open the pin is connected to GND using a “pull down” resistor, as shown in circuit (4).

A common value for pull up resistors is 10K Ohm. Higher resistance may be necessary for circuits that sink greater currents. We can use Ohm’s Law to determine the appropriate value for the resistor.

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This is an addendum to the LED control using DIP switch post, to include the schematic to the project circuit:

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2. LED Patterns Using DIP Switch and Arduino
3. Pull Up Resistors
4. Arduino Motor Control for the Spinning Night Light | Part 3

This is a very simple project that controls a set of LEDs using a DIP switch. The purpose of the sketch is to show the use of some Arduino serial communication functions, and to increase familiarity interfacing with digital I/O pins.

Two LEDs were connected to the RX and TX pins on the Arduino (digital pins 0 and 1), but remember to disconnect these pins while the sketch is being uploaded.

Parts list:

• Arduino Duemilanove
• Breadboard
• 8 LEDs, assorted colors
• Jumper wire, assorted lengths
• DIP switch
• 6 10K Ohm resistors (pull up)
• 8 100 Ohm resistors (current limiting)

Sketch:

// www.TheElectronicsHobbyist.com/blog
// Natalia Fargasch Norman
// LED control via DIP switches

// Arduino pins used for the LEDs
#define LED1 13
#define LED2 12
#define LED3 11
#define LED4 10
#define LED5 9
#define LED6 8

// Arduino pins used for the switches
#define S1 7
#define S2 6
#define S3 5
#define S4 4
#define S5 3
#define S6 2

// State of each switch (0 or 1)
int s1state;
int s2state;
int s3state;
int s4state;
int s5state;
int s6state;

void setup() {
  // pins for LEDs are outputs
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(LED3, OUTPUT);
  pinMode(LED4, OUTPUT);
  pinMode(LED5, OUTPUT);
  pinMode(LED6, OUTPUT);
  // pins for switches are inputs
  pinMode(S1, INPUT);
  pinMode(S2, INPUT);
  pinMode(S3, INPUT);
  pinMode(S4, INPUT);
  pinMode(S5, INPUT);
  pinMode(S6, INPUT);
  // setup serial port
  Serial.begin(9600);
  Serial.println("Serial port open");
}

void loop() {
  s1state = digitalRead(S1);
  digitalWrite(LED1, s1state);
  s2state = digitalRead(S2);
  digitalWrite(LED2, s2state);
  s3state = digitalRead(S3);
  digitalWrite(LED3, s3state);
  s4state = digitalRead(S4);
  digitalWrite(LED4, s4state);
  s5state = digitalRead(S5);
  digitalWrite(LED5, s5state);
  s6state = digitalRead(S6);
  digitalWrite(LED6, s6state);
  Serial.print(s1state);
  Serial.print(s2state);
  Serial.print(s3state);
  Serial.print(s4state);
  Serial.print(s5state);
  Serial.print(s6state);
  Serial.println();
}

A video of the project in action.

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1. LED Patterns Using DIP Switch and Arduino
2. Controlling a Seven-Segment Display Using Arduino Part 3
3. Controlling a Seven-Segment Display Using Arduino Part 4
4. Arduino 2-Digit 7-Segment Display with Buttons | Part 4

Computers can exchange bits of information serially (one after another, in sequence) or in parallel (several at the same time). In applications where it is necessary to have one computer talk to another, the most commonly used communication method is serial.

So it is no surprise that serial communication is the method used to send data between the Arduino board and a computer (or other device). Information is sent to and from the computer and the Arduino by setting a pin high or low. One side sets the pin and the other reads it.

The Arduino Duemilanove has one serial port that communicates on digital pins 0 (RX) and 1 (TX) as well as with the computer via USB. When you use the IDE to Upload your sketches to the Arduino, the bits are transmitted one at a time through the USB cable to the Arduino. The serial connection can also be used in our sketches to send data to the computer and to receive data from the computer via the serial monitor available on the IDE. This proves very useful for debugging your projects, as we will explore in the upcoming posts.

The Arduino serial library makes the following functions available for use in your sketches:

• begin(): opens serial port and sets the rate for serial data transmission (the RX and TX pins cannot be used for general input and output when the serial port is being used)
• end(): disables serial communication (this allows the RX and TX pins to be used for general input and output again)
• int available(): gets the number of bytes stored in the serial receive buffer (the buffer holds 128 bytes) that are available for reading from the serial port
• int read(): reads incoming serial data
• flush(): flushes the serial receive buffer of incoming serial data
• print(): prints data to the serial port as human-readable ASCII text
• println(): prints data to the serial port as human-readable ASCII text followed by a carriage return character and a newline character
• write(): writes binary data to the serial port

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The Arduino is based on the microcontrollers from Atmel. Here are current Arduinos available (the architecture is open source, and anyone can build their own “Arduino” based on the technical specs that are available for download from the official Arduino website).

• Duemilanove: “Duemilanove” means 2009 in Italian and is named after the year of its release. The Duemilanove is the latest in a series of USB Arduino boards. It is based on the ATmega328 and has 14 digital input/output pins (of which 6 can be used as PWM outputs) and 6 analog inputs.
• Mega: The Arduino Mega is based on the ATmega1280. It has 54 digital input/output pins (of which 14 can be used as PWM outputs) and 16 analog inputs.
• Nano: The Arduino Nano is a small, breadboard-friendly board based on the ATmega328 (Arduino Nano 3.0) or ATmega168 (Arduino Nano 2.x). It has more or less the same functionality of the Arduino Duemilanove, but in a different package.
• Bluetooth: The Arduino BT is an Arduino board with built-in bluetooth module, allowing for wireless communication. It features a surface-mounted ATmega168.
• Lilypad: A stripped-down, circular Arduino board designed for stitching into clothing and other fabric/flexible applications. It can be sewn to fabric with conductive thread. Lilypads are available on versions based on the ATmega168 or the ATmega328.
• Mini: The Arduino Mini is a small microcontroller board based on the ATmega168 (surface-mounted), intended for use on breadboards or when space is at a premium.

You might also enjoy:

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Schematic: A diagram of an electrical circuit that uses standardized symbols for the components.

Semiconductor: A material of electrical resistance between that of a conductor and an insulator. It is used to construct diodes, transistors, and integrated circuits.

Solder: A tin-lead alloy that becomes liquid when heated to above 360 degrees. It has low resistance, like other metals, and provides a strong mounting.

Switch: A device used to connect or disconnect the wires in an electric circuit, turning it on or off.

Transistor: A three-terminal, solid-state electronic device designed to amplify, oscillate, or switch the flow of current between two terminals.

Voltage: The measure of difference of electric potential across a material or between two points in a circuit.

Volts (V): The unit of measure for voltage.

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4. Starting Out on an Electronics Hobby – Resources

Insulator: A material that has high electrical resistance and is therefore a poor conductor of electricity.

Integrated Circuit (IC): A type of digital circuit in which transistors, diodes, resistors and capacitors are constructed on a semiconductor base.

Light Emitting Diode (LED): A type of diode that generates light when current flows through it.

Ohm’s Law: The relationship between voltage, current and resistance.

Ohm (?): The unit of measure for resistance.

Printed Circuit Board (PCB): A board in which components are connected using a thin coat of conductive material “printed” on the board instead of wires. It is used for mounting electrical components.

Resistance: The electrical friction between an electric current and the material it is flowing through that causes electricity to be dissipated as heat.

Resistor: An electrical component used to introduce resistance into a circuit.

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4. Starting Out on an Electronics Hobby – Tools

Digital Circuit: A circuit in which inputs and outputs have only two possible states: low (0) or high (1).

Diode: A two-terminal electronic device that allows current to flow in only one direction.

Direct Current (DC): Current that flows across a material in one direction only.

Disc Capacitor: A type of capacitor that has low capacitance and is used mostly in high frequency circuits. Disc capacitors are not polarized.

Electrolytic Capacitor: A type of capacitor that has high capacitance and is used mostly in low frequency circuits. Electrolytic capacitors are polarized.

Electronics: The science and technology concerned with and based on electricity and its applications.

Farad (F): The unit of measure for capacitance.

Ground: A common name for the reference point in an electrical circuit at which the measured voltage is taken to be zero.

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3. Basic Hobby Electronics Vocabulary Part 4 of 4 (S-V)
4. Starting Out on an Electronics Hobby – Tools

Alternating Current (AC): Current that is periodically reversing its direction of flow.

Ampere (A): The unit of measure for electric current. Commonly shortened to “amp”.

Battery: A device which uses a chemical reaction to convert chemical energy directly into electrical energy.

Capacitance: A measure of the electric charge that can be stored on a conductor; the ability of such conductors to store electric charge.

Capacitor: An electrical component that introduces capacitance in electric circuits.

Conductor: A material that has low electrical resistance and can therefore efficiently allow electrical current to flow through it.

Current: A measure of the flow of electric charge passing any point of a wire per unit of time.

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2. Basic Hobby Electronics Vocabulary Part 3 of 4 (I-R)
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4. Starting Out on an Electronics Hobby – Tools

Surround yourself with all things electronics:

Books: hobby electronics books on Amazon.com

Magazines:

• MAKE Magazine
• Nuts and Volts
• Everyday Practical Electronics
• Circuit Cellar

Read up on electronics online:

• electronics2000.co.uk
• Hobby Projects
• Hobby DIY Garage

Find good sources of electronics parts and components:

There are plenty of reliable electronics supplies stores online such as Parts Express, Jameco Electronics and CuteDigi. Also check out local junk yards and flea markets, and last but not the least, ebay.

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3. Basic Hobby Electronics Vocabulary Part 3 of 4 (I-R)
4. Basic Hobby Electronics Vocabulary Part 4 of 4 (S-V)

Whether your interest in an electronics hobby stems from the desire to build your own gadgets or to modify existing electronics devices so they perform better – or at least differently – it is important that you take the best approach possible in order to get the most enjoyment from your hobby.

When you are first starting out you should put together a kit of essential tools. A simple kit should have the following set of basic, good quality tools:

• Wire cutter and stripper
• Soldering iron and solder
• Soldering iron stand (optional)
• Desoldering tool (optional)
• Pair of small pliers – long nose pliers
  
• Screwdrivers – small straight type and medium cross point type
• Test equipment – multimeter (optional)

If possible you should get a wooden board/bench to use as a dedicated work area.

For introductory courses on electronics as a hobby checkout the website below:
http://www.hobby-electronics.info/links/courses.php

You might also enjoy:

1. Starting Out on an Electronics Hobby – Resources
2. Basic Hobby Electronics Vocabulary Part 1 of 4 (A-C)
3. Basic Hobby Electronics Vocabulary Part 2 of 4 (D-G)
4. Basic Hobby Electronics Vocabulary Part 3 of 4 (I-R)