Need audio vco circuit

Assuming square wave or triangle will do you, check out the VCO circuit on the LM324 datasheet. Can't get much cheaper/easier. If the speaker is low impedance you'll need a buffer on the output, or if you just need "audible", use a series resistor to knock the output current down to single-digit mA.

Best regards, Spehro Pefhany

that chip has been around all over. check it out.

How about a CD4046?

Sounds good, Ken...where can I find such a circuit?

You design it. The 555 has quite a bit if what you need, inside. It has the threshold sensor and the discharge switch. You add a flip flop to the pulse output to get a square wave. And you have to come up with a variable current source to charge the capacitor that is controlled by a second 555 oscillator to do the sweep. Hence the name of this group. ;-)

Please explain "find such a circuit" in this context. Do you mean find a CD4046? Do you mean find an existing application? Do you mean find a schematic with part values?

sorry, Ken I mean what does the schematic look like. I'm no designer. Thanks

Get a copy of the data sheet and app-notes for the CD4046 and read them, ignoring the stuff about the phase detector and looking carefully at the VCO section.

See a photo of an interactive spreadsheet calculator for the 4046:

Perhaps I could make a Win32 executable equivalent with MASM32. Uggh, another project. :)

-- "Rightousness is found within one's self, not in the demoralization or subjigation of others." MCJ 200411

Here's a practical circuit to get you started: