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Electronics Projects: How to Build Series and Parallel Circuits

By Doug Lowe

Whenever you have circuits that consist of more than one electronic component, those electronic components must be linked together. The two ways to connect components in a circuit are in series and in parallel.


In a series connection, components are connected end to end, so that current flows first through one, then through the other. In the series connection, the current goes through one lamp and then the other. The lamps are strung together end to end.

One drawback of series connections is that if one component fails in a way that results in an open circuit, the entire circuit is broken and none of the components will work. So, if either one of the lamps in the series circuit burns out, neither lamp will work. That’s because current must flow through both lamps for the circuit to be complete.

In the parallel connection, each lamp has its own direct connection to the battery. This arrangement avoids the if-one-fails-they-all-fail nature of series connections. In a parallel connection, the components do not depend on each other for their connection to the battery. Thus, if one lamp burns out, the other will continue to burn.

An interesting thing happens with voltage when components are connected in series: the voltages present at each component are divided up. For example, in a circuit with a 3 V battery and two identical lamps connected in series, each lamp will see only one and a half volts. If you connected three identical lamps in series, each lamp would see only one volt.

You can measure the voltage seen by any component in a circuit by setting your multimeter to an appropriate voltage range and then touching the leads to both sides of the component. The voltage you measure there is called the component’s voltage drop.

How to build a series lamp circuit

In Project 1-3, you’ll build a circuit that connects two lamps in series, a simple circuit. Then, you’ll use your multimeter to measure the voltages at various points in the circuit.

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How to build a parallel lamp circuit

In this project, you’ll build a circuit that connects two lamps in parallel and you’ll use your multimeter measure voltages within various points in the circuit.

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