By default, Eagle will automatically assign a name to our device when we place it on our schematic, making sure that each part is numerically unique. It does this by looking for the '>NAME' text that we inserted in our part, updating it with a unique name.
This allows us to distinguish parts during the manufacturing stage, but we can make things a lot easier for other engineers, customers or manufacturing partners by adding an optional one or two letter prefix to these names.
To add this prefix, we use the 'Prefix' button below the package list:
As with schematic symbols, there is a certain tradition and expection built up around part names, and when possible you should adhere to these standard naming conventions for your parts. Its expected that resistors will be named Rx, capacitors will be named Cx, integrated circuits (such as our sensor here) will be names Ux, etc.
The Wikipedia entry on Electronic Symbol contains a list of some of the most common prefixes, but when in doubt you can also have a look at some other schematics from trusted sources to see what prefix should be used with what device types.
Some of the most commonly used prefixes are shown below for convenience sake:
- C - capacitor
- D - diode (including LEDs!)
- J - header pins or 'jack' connector
- JP - jumper
- L - inductor
- M - motor
- Q - transistor/FETs
- R - resistor
- S - switch (TACT switch, etc.)
- TP - test point
- U - integrated circuit (sensors, MCUs, etc.)
- X - Wikipedia lists this last transducer, but it is often used to indicate connectors (USB, etc.)
- Y - Crystals or oscillators