Electronics > Beginners
Some noob questions
Brumby:
It is unfortunate that terms like "Earth", "Ground" and "Chassis" are all too often used to simply make reference to a common connection. When the familiar definition of these terms is not applicable, it really can be confusing.
This common connection is also frequently given the role as the reference point for other measurements. While this is not a guaranteed relationship, it would be rare to come across a schematic which did not do this.
The only time you can really be certain of a common connection being your reference point is when you have something described as 0V - such as a 0V power rail.
In practical terms, this reference point is (as you have worked out) where you would put the black lead from your DMM.
As you become more familiar with schematics and circuit topologies you will be able to make better judgements about reference points and measurements - but the first steps are understanding the simple things. Each of these can be mysterious and confusing, until it 'clicks'. Those are wonderful moments.
Mr D:
Thanks!
I feel like i've got just enough understanding to start looking at some real circuits.
Could anyone tell me: in the circuit below, how come i see no power source?
Or is that triangular element in the middle the power source? But it's not a battery, so what is it?!
Yeah yeah, this is a super-nooby question!!
rstofer:
The triangle is an op amp and the power supplies (probably +-15V) are not shown. This is typical of all op amp circuits used in tutorials. There might be an exception when the circuit uses a single rail op amp. Then the + power input will have some voltage and the - power input will have a ground symbol.
That' an awfully advanced circuit considering...
Here's a circuit that shows the power supplies:
http://www.learningaboutelectronics.com/Articles/How-to-connect-a-LM741-op-amp-chip-to-a-circuit
Mr D:
OK!
I'm not trying to understand the circuit, i'm trying to understand and make sense of the elements and general structure!
So is the circuit only missing the power supply to make it a complete, viable circuit?
rstofer:
It looks complete. The tricky part is that incandescent lamp in the upper left corner. That device is used as a non-linear resistor. When cold, it has very low resistance which means the op amp has very high closed loop gain. When the circuit is oscillating normally, the resistance will increase (because the current increased) until everything balances out with a value of Rf/2 so the op amp closed loop gain should be around 2.
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