colpits oscillator

[magno_grail]

Looking for a colpits oscillator based upon either an OP-amp or comparitor. The circuit already uses a window comparitor so there are two left over in the package. The circuit is a basic position indicator with a variable inductor input to a colpits oscillator feeding a V-F converter to the window comparitor. A dual green/red LED provides the output.
Thanks.

 

[Roff]

Are you looking for any particular frequency? How much does the frequency need to vary?

 

[magno_grail]

The frequency does not matter much. The inductor core will change from zero to full position in about a second. The position varies with operating conditions.
The range of frequency is whatever can be detected by a LM2907. The output voltage of this goes through a potentiometer to the window comparitor to set the high range limit. A potentiometer in the window circuit sets the low range limit.
I have seen a simple circuit that uses a single inverter gate with the inductor between the input and output and a capacitor from input and output to ground. However that requires an additional chip. I need to keep the parts at a minimum.

 

[Sebi]

What is the comparator type?

 

[magno_grail]

The comparitor will probably be a LM3900. Any single ended power supply type would work or a single supply OP-amp.

 

[Russlk]

The LM3900 is not a comparator or even an op amp; it is an amplifier with a current mirror input. It may work in your application, but you have to know how to use it.

Check out the colpits circuit in this URL, put ground at the transistor emitter, then substitute the LM3900 for the transistor: https://www.electronics-tutorials.com/oscillators/colpitts-oscillators.htm