Symbols and Reference Designators


These are the most common symbols you will see on schematics, and the reference designators that are used to identify them.
 
BT BT Battery
C Capacitor
C Polarized Capacitor
CR LED (Light Emitting Diode)
D Diode
D Zener Diode
D Thyristor
DS Lamp or Display
F Fuse
FB Ferrite Bead
J Connector (receptacle)
JP Jumper
K Relay
L Inductor
P Connector (plug)
Q Transistor
Q Transistor
R Resistor
RT Thermistor
S Switch
T Transformer
TP Test Point
U Integrated Circuit
U Gate Symbol (inverter)
U Op Amp
Y Crystal, Oscillator


Note that some reference designators are used for more than one symbol; whether a capacitor is polarized or not the reference designator is still "C". Be aware of the fact that this is not a complete set of symbols, just enough to get you started. For example, there are  many types of transistors, but only two are shown here. As a circuit board designer you probably won't have to know the difference between them, for now you just want to get a general idea of what they look like. Integrated Circuits are drawn as a rectangle with various numbers of pins coming out of them. Thousands of components share this symbol style and the "U" reference designator. Symbols for Power Supplies or Modules or Sub-Assemblies will also have symbols like this.

Two other categories you need to know about :
   - symbols that don't have reference designators
   - reference designators that don't have symbols. 

 
Reference Designators
that don't have symbols		 Symbols that don't have Reference Designators
FD Fiducial Circuit Ground
HW Hardware  
I In-Circuit Test Pt. Analog Ground
MH Mounting  Hole  
MP Mech Part Chassis Ground
Z RefDes Suppressed  
    Voltage Supply
     


!!!    YOU MUST READ THIS    !!!
VERY IMPORTANT FINAL NOTE 


None of this is set in stone, and every company or customer has slightly different preferences. I have never seen two companies do things the same way.
Take what you see here as a place to start, but try to learn their particular style as quickly as you can.
The first thing you should do is study some of their existing drawings. Some companies use "D" as the reference designator for LEDs, others use "LED". Some use a little circle for test points, some use that same symbol for voltages. Some use a rotated connector symbol for voltages. It doesn't really matter as long as it is clear and consistent. After you build up some experience you can suggest ways to standardize if you think it will help.
Go with the flow and don't make waves til you know what yer doin'.

And by the way, when you move to a NEW company and they do everything differently, don't bother saying "Well, at my last company we did it THIS way". Chances are, they won't care. (We'll talk about when its appropriate to take a stand a little later... )