I have a wein bridge which works very well. I want to vary its frequency based on a square pulse every 1.5 seconds generated by an 555 (or perhaps an MCU).
The way to vary its frequency is to modify the "R" of the RC or the "C" of the RC.
But it has to be said, in order for it to oscillate at all, the two RCs must be almost perfect matches, even better than 1%. I actually pull components out of the draw and measure them and pair them, else it will not oscillate.
So we cannot willy-nilly mess with the Rs or the Cs and expect it to work.
To modify the "R" I thought of an LDR, actually two LDRs driven by the same LED. However LDRs have a varying resistance of many MOhm down to a few hundreds Ohms. I think it would be impossible to attempt to use two LDRs and expect them to either stay within a sensible range or to track each other to 1% or better. But I have a ton of LDRs so I may just try it.
Another idea was to mess with the Cs. For that the only thing I found was "varicaps" or "varactors". So I have bought a few to try out. Never used them before.
I am looking for ideas. Here is a schematic of the Wein bridge oscillator as it is and with the varactors in place which works on simulation. Simulation of course has perfect components so it does not prove anything.
The way to vary its frequency is to modify the "R" of the RC or the "C" of the RC.
But it has to be said, in order for it to oscillate at all, the two RCs must be almost perfect matches, even better than 1%. I actually pull components out of the draw and measure them and pair them, else it will not oscillate.
So we cannot willy-nilly mess with the Rs or the Cs and expect it to work.
To modify the "R" I thought of an LDR, actually two LDRs driven by the same LED. However LDRs have a varying resistance of many MOhm down to a few hundreds Ohms. I think it would be impossible to attempt to use two LDRs and expect them to either stay within a sensible range or to track each other to 1% or better. But I have a ton of LDRs so I may just try it.
Another idea was to mess with the Cs. For that the only thing I found was "varicaps" or "varactors". So I have bought a few to try out. Never used them before.
I am looking for ideas. Here is a schematic of the Wein bridge oscillator as it is and with the varactors in place which works on simulation. Simulation of course has perfect components so it does not prove anything.
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