/ / Simple Circuit

A simple circuit is made from components that use voltage, current and resistance to perform some function.

Voltage

Voltage is the driving force in electronic circuits. It is what moves the electrons through the circuit.

Voltage can be supplied by a battery, solar cell, generator and power supplies like wall adapters. One refers to these sources as power supply or power source.

In a circuit the electrons flow from the negative terminals through the circuit to the positive terminals. When the electrons are energized, they move.

Current

Current is the movement or flow of electrons in a circuit.
Current represents the amount of electrical charge and is what gets work done. It is measured in amperes, symbolized by A.

Resistance

Resistance is the movement of electrons through a material that results in the occasional collision with atoms that restricts the flow of electrons. This restriction of flow is known as that material's resistance.This resistance creates a dispersion of excess energy in the form of heat. Materials with high resistance, like plastics, are poor conductors of electricity. Materials with low resistance, like copper, are great conductors. Resistance is measured in ohms.

/ /Prototyping a Simple Circuit

A basic circuit consist on a voltage source, a load, and a path for the current to flow between the voltage source and the load.

Materials

• 9 volt battery
• 3 alligator clips
• a resistor
• an LED

Steps

1. Determine what resistor you will need. Assume the LED has a forward current of 3V. Using Ohms Law: V=IR.
   Figure out what resistor you need in this circuit.
   1. Subtract the 3 Volts from the 9 volts to get the current less the Forward Voltage
   2. Assume the Forward Current for the standard LED is 30mA (0.03A)
   3. Using Ohms Law , find the resistance. When selecting a resistor, you might have to find the nearest standard value which is greater than your result.
   
   

   ---

2. Attach separate alligator clips to the positive and negative terminals of your battery.
   
   Use different colored alligator clips to help you visually distinguish the positive and negative terminals. The convention is red for positive and black for ground.

   ---

3. Connect the other end of the alligator clip attached to the positive terminal to the anode of the LED
   

   ---

4. Connect the short lead of the LED (the cathode) to your resistor.
   

   ---

5. Connect the alligator clip connected to the negative terminal of the battery to the other side of the resistor.
   

   ---

Electrons from the negative terminal flow through the alligator clips and through the LED, lighting the LED and flowing to the positive terminal.

/ /Using a breadboard

Breadboards are great for prototyping your circuits.

using a solderless breadboard

A breadboard is a tool for holding the components of your circuit, and connecting them together. It's got holes that are a good size for hookup wires and the ends of most components, so you can push wires and components in and pull them out without much trouble.

At left is a typical breadboard. The holes on the breadboard are separated by 0.1-inch spaces, and are organized in many short rows in the center, and in two long rows down each side of the board. The short horizontal rows in the middle are separated by a center divider.

On each side of this board are two long rows of holes, with a blue or a red line next to each row. All the holes in each of these lines are connected together with a strip of metal in the back. In the center are several short rows of holes separated by a central divider. All of the five holes in each row in the center are connected with a metal strip as well. This allows you to use the holes in any given row to connect components together. To see which holes are connected to which, take a multimeter and a couple of wires, set the multimeter to measure continuity, stick the two wires in two holes, and measure them with the multimeter. If the meter indicates continuity, then the two holes in question are connected.

Breaking it down in pictures

  What's inside?


The reason for the center divider is so that you can mount integrated circuit (IC) chips, like a microprocessor, on the breadboard. IC chips typically have two rows of pins that you need to connect other components to. The center row isolates the two rows from each other, and gives you several holes connected to each pin, so that you can connect other components.

---

When you start to put components on your breadboard, avoid adding, removing, or changing components when the board is powered. You risk shocking yourself and damaging your components.

	At left is a typical use of a breadboard. An IC chip (in this case a BX-24 microcontroller) straddling the center divider, connected to several of the rows of middle holes. At the top, a 7805 5V DC voltage regulator is connected to three of the middle rows Ground pin is connected to the blue rows of holes +5V output is connected to the red rows of holes. LED and resistor connected to the BX-24's bottom left pin (pin 12) in series.
	A second row of middle holes is used to connect the LED to the resistor.
	At left, the three LED's are connected in series using two rows. They are then connected to power and ground by connecting the rows to the red power row and the blue ground row.

Many options are possible using a breadboard, which is what makes them very useful and convenient for building circuits. Once you understand which holes are connected to each other (and which ones are not), you can build any circuit very quickly.

Keep your circuits neat

• Shorten the leads on components so there is no bare metal sticking up from the breadboard.
  
  
• Make sure no wires cross each other with metal touching (this is the biggest source of short circuits on a breadboard).
  
  
• Lay things out as sensibly as possible, so each component of the circuit is neat.
  
  
• Use wires when needed to separate parts of the circuit that are crowded together.
  
  
• Use consistent colors of wires when possible; for example, use green or black for ground connections, red for power connections, white or blue for data connections, and so forth. (Good for troubleshooting).
  
  

Don't do this:

Wiring basics

You need to add a voltage regulator to your breadboard because you only want to allow 5 volts into your circuit. We will use the LM7805 :

Output is what you want to link to your power line of your breadboard.

Front view


Back view

Also you want to connect both power and ground sides together:

---

Shorts A short occurs when a circuit is wired improperly and the current flows through the circuit along an unintended path. When a short happens, the circuit can result in damaged electronic components if an accidental surge of high current flows through them. It is dangerous to short a battery. Your battery could overheat and explode if shorted. If you think you have a short in your circuit, quickly disconnect the power supply.

/ /Using a breadboard

Wire up your circuit on the breadboard using a wall adapter and a voltage regulator

Materials

• Wall adapter
• breadboard
• a resistor
• an LED

Steps

1. Connect the power supply to the board with a voltage regulator
   
   

   ---

2. Connect the power and ground buses
   
   

   ---

3. Determine what resistor you will need. Assume the LED has a forward current of 3V. Using Ohms Law: V=IR.
   Figure out what resistor you need in this circuit.
   1. Subtract the 3 Volts from the 5 volts to get the current less the Forward Voltage
   2. Assume the Forward Current for the standard LED is 30mA (0.03A)
   3. Using Ohms Law , find the resistance. When selecting a resistor, you might have to find the nearest standard value which is greater than your result.

Part 2

Once that works add a second LED in serial

Part 3

Once that works connect the second LED in parallel

Click here for how to connect the LEDs