CIRCUIT SYMBOLS To allow people to document a circuit and everyone to be able to understand it there is a standard set of circuit symbols. These can be draw and connected together with lines to give a complete circuit like the one shown on the right. This module teaches you what the various symbols look like.

POWER SOURCES  The above symbol shows a single battery or cell. When more than one is to be shown, we draw two batteries with a dotted line and write next to it the voltage or number of cells. The final symbol is for a power supply and would be labelled with the voltage.

RESISTORS  These circuit symbols show various resistors. The above is a standard resistor all of the other resistors add to the same basic shape. Capacitors & Resonators  The left two symbols are capacitors, the 2nd being an electrolytic capacitor, where the plus sign indicated which way to connect the part. The other two are resonators, the first is a standard resonator and the other has an extra ground connection pin. .

LOGIC GATES  The 1st logic gate is an AND gate. Next to it is a NOT gate, on this you will see a small circle this indicates NOT. So the original AND gate with a circle on the output is a NOT AND (NAND) the last two are OR and NOT OR gates.

SWITCHES  Here are the symbols for a reed switch (activated by a magnet), a relay and also an opto switch, some times called and opto coupler.  The first two switches are push button switches, a push to make contact and a push to break. The other four switches are toggle or slide switches and show a number of versions from a basic single pole single throw switch up to a double pole double throw switch.

OUTPUT DEVICES  These are a selection of output devices. The difference between a buzzer and speaker is that when powered the buzzer outputs a tone at a set frequency, where as the speaker needs to be driven with a square wave. The remaining devices don't need an explanation

MISCELLANEOUS SYMBOLS  These are final set of symbols that don't fit into any particular category.