Circuit to output signal to headphone

[goldfinder]

Do any of you wizards have a good simple circuit that will output a variable frequency signal to the headphones. Frequency should be correlated with detection circuit voltage, zero voltage = very slow pulse, output frequency increases as voltage goes up. I tried a 555 timer circuit but it didn't seem to work all that well but maybe it wasn't that good of a circuit.

Any help greatly appreciated.
Thanks in advance!
Goldfinder

[BillBert]

Sorry for such a crude answer, but perhaps this may help:

http://www.seekic.com/forum/22_circu...UENCY_VCO.html

Where are you getting the voltage from?

[goldfinder]

Sorry for such a crude answer, but perhaps this may help:

http://www.seekic.com/forum/22_circu...UENCY_VCO.html

Where are you getting the voltage from?

Thanks Bill Bert,
I have a space problem and your circuit while looks great has too many parts to fit in space a I have left on the board and box.

Voltage is from a jfet amplifier.
Goldfinder

[Carl-NC]

A 555 can make a good VCO. See the Hammerhead circuit for an example. The trick is to feed the RC with a current, not a voltage, so you need a V-to-I transistor.

[goldfinder]

Many thanks Carl

A 555 can make a good VCO. See the Hammerhead circuit for an example. The trick is to feed the RC with a current, not a voltage, so you need a V-to-I transistor.

Carl,
the transistor trick is what I needed. I'll give it a try.
Goldfinder

[goldfinder]

Schematics - where

Carl,
I have a problem finding up to date schematics. With 100's of posts for a particular project it is very difficult to find a recent schematic and the associated PCB. Is there a specific place to get these?

Goldfinder

[porkluvr]

Carl,
I have a problem finding up to date schematics. With 100's of posts for a particular project it is very difficult to find a recent schematic and the associated PCB. Is there a specific place to get these?

Goldfinder

No, I'm not Carl. And you're right it is sometimes difficult to get easily digestible search results. It used to be easy but things got complicated and information got scattered.

You'll find the Hammerhead about 2/3 down the third page.
Also look for

[goldfinder]

Found it - Thanks Porkluvr

Thanks for directions.
Found the 555 VCO.
Goldfinder