Electronics > Beginners

no IC but U no T but Q

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I've wondered for a long time why in schematics IC's are always marked as U followed by a number when I'm sure it used to be IC which makes sense and transistors were always T but now are Q.

Can anyone think of any others like this ?

U makes sense to me because I see it as standing for Unit.

I don't know about transistors. I think Q is an Americanism. I prefer to use Tr rather than T which could mean transformer, although I admit to using Q also because it's the default for some of the schematic programs I use.

I don't know why L is used for inductance and I for current. I suppose C can't be used for current because it can easily be confused with capacitance and I can't be used for inductance because it would be confused with current.

L for inductance is named after Heinrich Lenz.
I for current is the abbreviation of the French, intensité.
Q for transistor is due to the quiescent (Q) point.
U, I'm not sure, but 'unit' sounds like a good guess.

I suspect it's just a case of what letters are left. You want a single character to save space on a silkscreen, and I is undesirable as it looks like a one.
Transformers predated transistors which would explain Q as a probably fairly arbitary choice.

Off the top of my head I've seen :

A ?Antenna
B Battery, Bridge rectifier, pushbutton
C cap
CR diode (Crystal rectifier)
D diode
F fuse

I Undesirable as it looks like one
J Jack
K Relay (clicKy thing?)
L Inductor
LP lamp
M Meter, motor, MOV
O Undesirable as it looks like zero
P Pot or plug/pin header
Q Transistor
R resistor
RV variable resistor
S Switch (or SW)
T transformer, thermistor
V Valve/Gasfilled tube e.g. neon, varistor
VR variable resistor
W wire link
X Crystal
Y Crystal
Z Zener

so maybe it is something dictated by the fact that more of us can make our own boards and it starts backwards from the fact that you don't want to use something like IC in a schematic that will then transfer to the layout with IC being easily misread


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