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Variable capacitor circuits

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I think walters needs this question asked to him again:

What are you trying to achieve?

I mean why would you want one formula for input, RC time, and phase? To me it is senseless to try to combine everything into one formula.
I only look at the RC time. Input is just input. and if the input is a speaker, check it's resistance, and then treat it as a resistor.
 
mstechca said:
Input is just input. and if the input is a speaker, check it's resistance, and then treat it as a resistor.
The low frequency resonance of a speaker causes it to be a lousy microphone.
Try making an allpass filter, a variable phase shift or a comb filter with just a speaker.

I know what you can do with the speaker: spin it! :lol:
 
audioguru said:
I know what you can do with the speaker: spin it! :lol:
In fact, connect a speaker to a circuit of some sorts, and to a motor, and see if you can power the motor from the techno music in the room! :lol: :lol:
 
varactor diodes the capacitances are in the picofarads

Can i use Varactors in "series" to increase the capacitances?

Or i would need a "Custom" Varactor diode to have the capacitance in the microfarads?

What would the Varactors doping process do different and how? the PN junction needs to be Bigger?


I need a Varactor is the Mircofarads? which ones is there please?
 
walters said:
varactor diodes the capacitances are in the picofarads

Can i use Varactors in "series" to increase the capacitances?

Or i would need a "Custom" Varactor diode to have the capacitance in the microfarads?

What would the Varactors doping process do different and how? the PN junction needs to be Bigger?


I need a Varactor is the Mircofarads? which ones is there please?

varactors a reverse biased diodes with specific dopping to act it as 'varactor' .
and u cannot (practicaly)get a uF varactor.
hava a look at
http://en.wikipedia.org/wiki/Varactor
http://www.vias.org/simulations/simusoft_varactor.html
**broken link removed**
 
thanks for the help

How can i get a a uF varactor?

I need uf Varactors?

How can i make one or put them in series or so to make a uf varactor?
 
A large depletion layer region large area would give me more capacitance to be mircofarads?

Most Varactors are used:
tunable filters and oscillators , frequency multiplication and frequency mixing
 
walters said:
A large depletion layer region large area would give me more capacitance to be mircofarads?

Most Varactors are used:
tunable filters and oscillators , frequency multiplication and frequency mixing
walters
u have a 1000 1PF capacitors , how would u make a 1uF capacitor out of it?
 
Yea but i still can't Vary the Varactors in Mircofarads i need to have a variable .01uf or .47 or 220uf Varactors i wish they made these

I need to use the .01uf Varactors in a phase shift network filter for audio not radio
 
walters said:
Yea but i still can't Vary the Varactors in Mircofarads i need to have a variable .01uf or .47 or 220uf Varactors i wish they made these

I need to use the .01uf Varactors in a phase shift network filter for audio not radio
audioguru wrote :
A 0.22uF capacitor's effective value in a filter circuit can be changed with PWM. With 100% duty-cycle it is 0.22uF. With 10% duty-cycle it is 0.022uF. With 1% duty-cycle it is ..., you figure it out. Of course, the frequency of the PWM is very high so can't be heard.
Repeat
You also didn't hear me describe how PWM can vary the capacitance over a wide range of any capacitor. I've used switched-capacitor lowpass filter ICs for years. They switch internal capacitors similar to PWM and work perfectly.
 
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