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Basic Function Generator help
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MarkF:
It looks like your power is NOT connected properly.
The LM324 pin 4 connected to +9V (red wire in picture) and pin 11 connected to -9V (yellow wire in picture).
The GND (black wire in picture) connected to the capacitor and 22K resistor.  The GND appears to be missing (See 2nd picture).



MarkF:

--- Quote from: dcbrown73 on August 10, 2019, 03:03:56 pm ---
--- Quote from: bjbb on August 10, 2019, 02:55:59 pm ---Missing a 'ground' equipotential that would be the return reference.

--- End quote ---

Are you referencing the cap not being connected to ground in the first picture?   

The second picture shows I did connected, it just wasn't connected in the first image.

That begs the next question.  Since the rails are +9v / -9v.  Do I actually require a GND (0v) potential also?

For instance, when I measure the waveform with my scope.  Do I connect the gnd connection to the -9v rail?

It's a bit maddening.  Earlier someone said you need to ensure my rails are +9v / -9v for this to work, but I saw a video of someone powering the entire thing with a 9v battery which didn't produce a -9v rail.

--- End quote ---

Connect the +/-9V rails to the op-amp only.
Connect the GND of power supply to capacitor, 22K resistor and scope GND.
You need all three connections from the power supply.
dcbrown73:
I've been an IT engineer for well over 20 years (servers, storage, networks, and software development) and I have never had anything that stumped me the way this little simple circuit is while trying to get it to function.  I feel like throwing the entire thing into the fireplace!  I don't have this issue with other circuits I've tried to replicate as a learning experience.

Given I'm not an electrical engineer I'm going to create a legend that will properly explain my terms since I could be naming one incorrectly and I want to eliminate confusion.

If I say positive rail.  I'm talking about +9v rail. (DMM tested to show +9v)
If I say negative rail.  I'm talking about the -9v rail (DMM tested to show -9v)
If I compare the positive rail to the negative rail, I show a 18v potential difference. (DMM tested)
If I say gnd.  I'm talking about 0v rail.  By 0v rail, I mean if tested, it shows +9v compared to the positive rail, and -9v compared to the negative rail. (DMM tested)

The 1uF film capacitor is connected to the 100k pot and the gnd rail.
The normally gnd pin of the 100k pot is left unconnected.
The the negative side of the 22k resistor connected to the voltage divider is connected to the gnd rail. (not the negative rail)

Those are the only two connections to gnd.  I can connect the pot's ground pin to gnd, but someone said not to.

Tested pins of the op-amp as measured against gnd.

* Vcc: +9v
* Vee: -9v
* +input: 11.5mV
* -input: -18.6mV
* output: 15.5mV
It seems to me the op amp just isn't turning on and I haven't the slightest idea why.  If I test on everycircuit, if I lower the inverting input below the non-inverting input.  The opamp comes on.   It seems based on the measurement above, the inverting input is at a -29mV potential difference, yet the opamp remains off.

Do I need a pull up/down resistor?

In the picture below.  The PSU jumpers as are follows:

* Red Banana Plug: +9v
* Black Banana Plug: -9v
* Yellow Banana Plug: GND


Audioguru again:
A "volume control" has a ground terminal. The pot in your circuit is a variable resistor, not a volume control.
Your circuit is not oscillating maybe because your variable resistor is set to be a resistance that is much too low.
dcbrown73:
I was poking around the circuit and measured the resistances way above expected on the voltage divider, so I moved the voltage divider away from the op amp and reconnected everything.  Now I get an (almost) perfect square wave and the pot controls the duty cycle.

Something was off about it, but it seems to be functioning perfectly now.   At least  I know I'm not crazy now...



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