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sparkfunbluesmirfsnippet.png

Kevin asks:

What do all those little subscript letters and numbers after V on circuit diagrams mean Vcc, Vee, Vss mean?

I have to admit, I didn’t really know the full answer to this one, so I looked it up. I found a page on the solarbotics website explaining the whole shebang: Vcc and Vdd mean that that point in the circuit is directly connected the power source, and Vee and Vss mean that point it is connected to ground. It went on to say:

Apparently this terminology originated in some way from the terminals of each type of transistor, and their common connections in logic circuits (i.e., Vcc is often applied to BJT collectors, Vee to BJT emitters, Vdd to FET drains, and Vss to FET sources). This notation then carries across to integrated circuits — TTL ICs were originally based on BJT technology, and so often use the Vcc / Vee terminology; CMOS ICs are based on FET technology, and so often use the Vdd / Vss terminology.

The absolute distinctions between these common supply terms has since been blurred by the interchangeable application of TTL and CMOS logic families. Most CMOS (74HC / AC, etc.) IC data sheets now use Vcc and Gnd to designate the positive and negative supply pins.

Image is a snippet of the schematic for SparkFun’s BlueSMiRF.

Have you got additional information? Post it in the comments! Have a question for Ask MAKE? Shoot me an email at [email protected] or drop us a tweet! We’d love to answer your questions on anything MAKE-y.

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Becky Stern

Becky Stern is director of wearable electronics at Adafruit Industries. Her personal site: sternlab.org


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