User Guide

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Figure 1. Three types of circuit – closed (left), open (middle), and short (right).
In a closed circuit, electricity can flow from the + terminal, to the
- terminal (ground in digital electronics). It passes through the
LED, which causes it to glow. But in an open circuit, electricity
cannot flow all the way around to ground so it does not move at
all. In this example, the LED does not light. A switch works by
opening and closing the circuit.
A short circuit can be dangerous. There is a direct connection
between the + and - terminals on the battery. With no
components in between, there is nothing to use or limit the
amount of electricity that flows.
Voltage is the amount of force that pushes electricity around a
circuit and it is measured in volts (V). For example, 5 V or 9 V. You
will often see 3.3 V written as “3V3” in diagrams where a dot
might be difficult to read.
Current is the amount of electrical charge in a circuit. It is current
that makes things happen, like lighting an LED. It is measured in
amps and this is shown with an A. For example, 1 A or 3 A. But
electronic circuits usually use very small amounts of current, and
1 Battery or power source. This supplies the circuit with electricity.
2 Light-emitting diode (LED). When power flows, it lights up.
3 Resistor. See below.