Re: voltage to resistance convertor?

Andrew Howard wrote:

> This is the circuit that needs the variable resistance. It is the
> basis for a simple phaser. Apparently it works by using the fact that
> the emiiter is 180 degrees out of phase with the collector (or
> something). The varying resistance has been labelled R1.
> VCC
> + (9V)
> |
> |-----'
> .-. .-.
> 47K| | | |2K2
> | | | |
> '-' '-' 1uF
> | | +[/
> 1uF | '----[|------'
> \] | |/ [\ | |
> IN o------|]---o---| BC548 | | 1uF
> /]+ | |> .-. | \]
> | .----' | |<-----|]----o OUT
> o | | | | |2K5 /]+
> | .-. .-. | '-'R1
> === 22K| | | | | | o
> GND | | | |2K2'---' |
> '-' '-' ===
> |-----' GND
> |
> ===
> GND
>
>
> (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)
>
> I have decided that I would prefer a sine wave, if that makes any
> difference to anything. Both the phaser circuit and the sine wave
> generator will be using the same power supply.

The circuit looks faulty as you have drawn it.
Look at the signal path from the collector, through a 1uF, to the wiper
of R1, through a 1uF, to the output.
That is a very low impedance path, practically a shortcircuit for AC
signals. The collector signal will be at the output in full force, no
matter how R1 is set.

Now you want to mix into that signal the opposite phase from the
emitter, by using R1, and what effect do you want to achieve by that?

I think the signal from the emitter will hardly be stronger that the
collector signal, so the result will be an attenuation of the signal,
which could be achieved a lot simpler, if that is what you want.

Maybe you have made a mistake in the drawing, so the connection between
the collector output cap to the wiper of R1 should be erased?

Then we will at least get something meaningful, a circuit which can
move between positive phase, through nothing, to negative phase, by
moving the wiper of R1.

If we replace R1 with a pair of FET transistors we can voltage control
how much positive or negative phase goes to the output. Or by using
analog gates, type 4066 series, the same effect can be achieved.

But basically I think the whole project seems badly concieved and
designed. What you really need is to start over from the beginning,
make it clear what you want to achieve, and ask for help to design a
circuit to do that.



--
Roger J.
.

Relevant Pages

  • Things pyrazo related...
    ... Introducing the Pyrazo circuit. ... This circuit induces a oscillation from a oscillation source to be ... through the primary of the pulse transformer. ... The device may be used to absorb or amplify signals from any signal ...
    (sci.energy)
  • Re: Proper use of differential outputs
    ... ie they tie one input line to their circuit 0V. ... this make use of differential signals pointless? ... Is there any reason not to use coax? ... I've considered and dismissed a couple of tricks I figured were too high risk like a notch filter to get rid of hum; but I've added a 300kHz linear phase filter to reduce HF fuzz, and an isolated power supply to get rid of earth loops. ...
    (sci.electronics.design)
  • Re: Need experts for vexing hum problem
    ... It would seem the star grounding has worked; the 120 Hz hum is now ... filament circuit isolated (and maybe tied to the chassis with a small RC ... What do you mean by ordering resistors to step down the scope probe ... You will be looking for signals in the microvolt ...
    (sci.electronics.design)
  • Re: high voltage discharge emi problem..
    ... discharging a high voltage capacitor through a Spark Gap, a triggering ... The trigger circuit is fully isolated using an isolated supply ... low-level sensitive signals away from loops with high-power signals. ...
    (sci.electronics.design)
  • Re: 1740a oscilloscope positioning problem
    ... yes its much harder to trace the signals when u dont know which ... circuit so cuasing a considerable dc imbalance, its a pnp device - motorola ... the trace has disapeared off the screen on all ... > coupling is selected) to the vertical deflection plates of the CRT. ...
    (sci.electronics.repair)