Stupid Newbie, Circuit problems

Ok, so I'm a noob!

Firstly, on basic electronic project circuits, when I see (eg) +9v and an earth symbol on the sircuit, do I connect a nine volt cell positive end to the +9v connection, and the negative end of the cell to the earth?

Also, what do I do on the attached circuit, do I run 2 9v's in parallel, +9v to the positive end of the battery, -9v to the negative end, and earth to the join between the two cells?

Cheers!

PS. Copyright not owned by me for this circuit: Fair use, limited resolution screenshot for education.

And above the photo transistor the diagram reads "NC" I assume that means don't connect that connection to anything?

zanes said:

Firstly, on basic electronic project circuits, when I see (eg) +9v and an earth symbol on the sircuit, do I connect a nine volt cell positive end to the +9v connection, and the negative end of the cell to the earth?

Click to expand...

Yes.

Also, what do I do on the attached circuit, do I run 2 9v's in parallel, +9v to the positive end of the battery, -9v to the negative end, and earth to the join between the two cells?

Click to expand...

I think you mean connect the 9V batteries in series and connect the earth to the point in between the two batteries.

Also note that you don't need to physically the earth symbol to the ground, in most cases it's just a reference point; if a circuit actually needs earthing the text explaining it will say so.

Cheers!

PS. Copyright not owned by me for this circuit: Fair use, limited resolution screenshot for education.

Click to expand...

No problem, it's called fair dealing over here and yes posing circuits from books is fine providing you don't rip whole chapters.

And above the photo transistor the diagram reads "NC" I assume that means don't connect that connection to anything?

Click to expand...

Yes, it stands for No Connection.

I think it is a stupid circuit.
The very old 741 opamp is inverting with a very low 1k input impedance produced by R2. But the impedance of the photo-transistor is 270k which is produced by R1. Then the photo-transistor is shorted by R2. DUMB!

The opamp should have a high input impedance of 2.7M so it doesn't load-down the output of the photo-transistor. Then the opamp should be a more modern FET input type and be non-inverting like this:

Cheers guys, Hero999 that is what I meant, audioguru I don't know about that, its out of a book collection of old popular mechanics articles/ projects. Best practical introduction to practical circuits I could find!

Popular Mechanics magazine had electronic circuits?
They know as little about electronics as a chef knows about medicine.
DUMB!

audioguru said:

Popular Mechanics magazine had electronic circuits?
They know as little about electronics as a chef knows about medicine.
DUMB!

Click to expand...

Bum, meant modern electronics!

Maybe the stupid circuit designer is sneaky.
Maybe he planned the very low input impedance of the inverting opamp to be an attenuator. Then he could use excessive gain for the opamp which reduces its bandwidth. Then he didn't need to add two capacitors. SMART?