Schematic Simplicity

If you have been following these guides from the beginning, then you are pretty familiar with schematics that have a battery, and a large loop for current to flow in a circle in. This is a perfectly valid way of representing a circuit. However, many designers prefer a slightly abbreviated version. Lets take a look at an example.

Circuit with Loops	Circuit with GND and V+

These circuits are equivalent.

The reason many people prefer the layout on the right is it makes the circuit look less complicated. Each system that has a signal going through it is going to need +V and GND, so the special symbols for +V and GND above are used instead of drawing long lines all over the schematic.

Transistor Example

In our Transistor Guide we modulated the speed of a motor with our voice using a microphone (really a speaker), an FET and a motor. Lets look at that example again, only this time we are going to draw it with +V and GND symbols.

Circle Method	Signal Method

These circuits are electrically identical.

On the left is what we will call the "circle method" of drawing this circuit. Where are the systems? Where are the signals? It is less clear because the battery and GND connections get in the way. However, using the "signal method" on the right the two systems are more isolated. With the systems isolated it is much more clear which wire carries the signal from the microphone to the FET. See below.

In this example, System #1 is the Microphone and its connection to GND. System #2 is the motor, FET and their respective power connections. After circling the two systems, the signal wire connecting the two is the only thing that is left.

We made up the names System #1 and System #2. You can call them whatever you want.

A Couple Little Things To Note

In general, signals travel in circuits horizontally and from left to right like we read. However, this is not a hard and fast rule; there are plenty of times where signals travel from right to left or vertically.

Also note that there is a second, unused signal in the circuit above. Can you spot it? Its the wire between the FET's Drain and the bottom of the motor. The voltage on that wire is not 0V because it is not connected to GND, and it is not +10V because it is not connected to +10V. It is actually a signal voltage, somewhere between 0V and +10V that will change as the microphone picks up sound. If this is confusing, don't fret it, it will make more sense later.

Lastly, the +V in a circuit is frequently referred to as Vcc. This is sort of a throwback to BJT transistors when the + rail was connected to the collector leg of the transistor. Collector is the 'c' in Vcc. So when you see Vcc, just think +V and you'll be fine.

Conclusion

We feel that this is a necessary first guide in our Intermediate Electronics Fundamentals series of guides because many schematics can be analyzed in terms of signals and systems. In addition, it is necessary to learn to read schematics that have +V or Vcc and GND in them since many circuits shared on the web are drawn this way.