For a test of a filter and video transmitter gear, I need a variable frequency (potentiometer adjusted) sine or square wave oscillator, adjustable from about 1 to 10 MHz. Output about 1Vp-p okay, but I could reduce a higher output. I don't have many parts at the moment; so I need the cheapest way to do this. I have a lot of NOR gates lying around and I'm thinking of a ring oscillator but when I try to make them adjustable they become unstable.
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How about an oscillator around a Schmitt-Trigger inverter? Capacitor on input, resistor from output to capacitor, done.
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1\$\begingroup\$ has to be a schmitt-trigger; without the hysteresis it will just settle at a voltage somewhere near the middle of the rails. \$\endgroup\$– JustJeffApr 29, 2011 at 1:33
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\$\begingroup\$ Is there any drawback to using an op-amp based schmitt trigger over one of the 74HC14s? \$\endgroup\$– drxzclApr 29, 2011 at 7:53
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1\$\begingroup\$ @Ranieri - not really. I posted this because it's the absolutely minimum component count solution. It has fixed trigger levels, however, in the opamp version you can set the trigger levels yourself. \$\endgroup\$– stevenvhApr 29, 2011 at 8:01
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1\$\begingroup\$ Getting an op amp circuit to oscillate at 1 MHz to 10 MHz will be very difficult! \$\endgroup\$ Apr 29, 2011 at 10:07
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1\$\begingroup\$ @Leon - you're right (I forgot the frequency requirements for a moment.) \$\endgroup\$– stevenvhApr 29, 2011 at 13:14