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VOLTAGE CONTROLLED RESISTANCE for monostable multivibrators?

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LeftRights

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My intrest of the moment is making different joystick type controllers for the computer. Doing this basically means controlling the pulse width of a monostable multivibrator with a resistance capitance circut. Since the cap is fixed, I need to change the resistace. Easy? Well...I want to do it with voltage. So :arrow: :arrow:

I need a voltage controlled resistor that can handle the voltage (5v). Does that rule out MOSFETs? Can I get anything linear? I think there must be a way to control monostable MutiVib's with voltage, Does anyone know what it is???

Thanks for reading and helping... :D :D :D
 

crust

Member
You can sometimes use a FET by connecting the drain and source as your resistor and controlling the gate voltage. There is a company (I believe it is siliconx or something like that) that used to make some FETs specifically for this purpose. But whether you can do this depends on your circuit parameters. When using regular FETs, I have found that this works much better on paper than in practice.
 

Sebi

Active Member
The simply solution is a VCO, or an ICL8038 function-generator chip. The output frequency controlled by voltage.
 

LeftRights

New Member
Sebi said:
The simply solution is a VCO, or an ICL8038 function-generator chip. The output frequency controlled by voltage.
the problem that I have using this solution is that the Multi vibrator is a part of the computer so I can't "sub" another part in. I think that this is what you are suggesting??
 

motion

New Member
The function of the resistor in the RC circuit of a multivibrator is to control the charging rate of the capacitor. Instead of trying to vary the resistance from a voltage source, a simpler and straightforward approach would be to use the voltage source to control a current source. A voltage adjustable current source would be easier to make. BTW, this is also how VCO circuits work.
 
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