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Building Circuits On Protoboard

Introduction to using Protoboard

Protoboard, sometimes refered to as breadboard, is a tool for quickly building and prototyping circuits. Components can be easily inserted into the protoboard without soldering and the internal connectors inside the protoboard connect the components together. These internal connectors are called tracks or rails - tracks are quite short, rails tend to be longer. A basic protoboard is shown below and the connectors are revealed to show which sockets are connected and which are separate. The two rails running horizontally along the length of the protoboard top and bottom are for the power supply connections and the short vertical tracks are used to connect different components together.

protoboard diagram protoboard from the top protoboard from below

The top and bottom rails are connected along the length of the protoboard - these are used for power supply connections for all components in the circuit. The circuit below shows the battery connected to the power supply rails. Components must link from one track to another - components should never have both legs plugged in to the same track or there will be a short circuit. The RED LED and resistor in the circuit below are connected using the vertical tracks - notice how each component crosses a gap between one track and the next and a wire link is needed to make the connection from the positive rail to the resistor. The GREEN LED is also correctly connected. In this case the resistor is directly connected to the positive rail and this connects to the LED, a wire link is needed down to the zero volt rail. Finally, the buzzer is simply connected to the power supply rails.

The close up shows the LED connections in detail. A RED wire links from the positive rail, crosses the gap and connects to a spare track. The connections in the protoboard mean the lower end of the RED wire is now connected to the upper end of the resistor. The resistor crosses the central gap and the lower end of the resistor is now connected to the upper end of the LED. The LED bridges the gap at the bottom of the protoboard and connects to the zero volt rail.

simple protoboard circuit diagram simple protoboard circuit layout simple protoboard circuit simple protoboard circuit closeup

Reasons to build circuits neatly

It is very important to build all protoboard circuits neatly and carefully! This is a skill that you should strive to develop whenever you are building protoboard circuits. Quickly built circuits that are messy rarely save time and effort in the long run.

Reasons to build circuits well:

Do do these:

tidy protoboard circuit

Do NOT do these:

messy protoboard circuit

More Complex Circuits

More complex circuits are built in the same way as simple circuits with the following points to bear in mind:

astable circuit astable protoboard circuit

Specific components used in many circuits

Push button: The wires for a push button must not stop the push button from functioning and so it is not a good idea to force the wires close to the push button. For the push button shown, bring both wires out from beneath the button so that there is plenty of space for the button to operate. The circuit shows the configuration for a pull down resistor and for a pull up resistor. There are other arrangements that would work equally well depending on the type of push button used.

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Potentiometer: The three wires for a potentiometer should all be taken from the same row on the protoboard so that the three wires are next to each other. This prevents the circuit being too crowded and also means it is easy to see the connections. In the circuits below, the blue potentiometer is being used as a three terminal potentiometer to provide a variable voltage. The cream potentiometer is actually connected as a variable resistor as one of the legs is not connected. The variable resistor then forms part of a potential divider.

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LED and resistor: An LED almost always has a series resistor. It doesn't matter in what order the resistor and LED are connected but it is usually more convenient to have the resistor followed by the LED. It is a very common mistake to simply wire the resistor and LED in a straight line (as is shown on a circuit diagram) but this simply short circuits the resistor leaving the LED with no protection. The circuit below shows LEDs connected as outputs from a pair of logic gates. The RED left hand LED is incorrect because the resistor simply connects from one pin of a track to a different pin of the same track and is short circuited. Resistors should always lead away from ICs horizontally.

protoboard components

IC e.g. 555: When wiring up an IC always start with the power supply wires so that you don't forget about them later on. Work carefully around the IC so that each connection is neat and has enough space. Remember, you don't have to connect the wires right next to the IC, anywhere in the correct track will do. Do not loop wires over the top of the IC. It is a good idea to have the circuit board layout and the circuit diagram bear some resemblance to each other.

protoboard components

Transistors: To avoid confusion, always wire a transistor up with all three legs in a straight line - even if the legs are arranged in a triangle on the actual device. In keeping with the comments for the push buttons and the potentiometers, always make all three connections from the same side to make it easier to see the layout.

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