Re: Terry's DRSSTC - Frequency/Pulse Width Controller

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Terry,

On 13 Dec 2004, at 17:18, Tesla list wrote:

> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi All,
>
> For my DRSSTC, I was going to have two knobs.  A 100k single turn pot
> in series with a 1k resistor to do the pulse width and basically act
> as a power controller following Steve's suggestion.  And another pot
> set up just like it (maybe a ten turn) for the pulse width.  The
> "linear" pulse width thing is easy with a LMC555 timer.
>
> However, most LMC555 circuits and their types are  "F : 1/R"  type
> circuits so the frequency control is not at all linear.  I was
> thinking zero on the pot would be like 1Hz, 25% on the pot 250Hz, 50%
> on the post 500Hz, 100% on the pot 1000 Hz...
>
> I just wanted to check to see if anyone and an easy simple way to do
> that?  I checked around for ICs and such, but did not find any
> wonderful solutions.  I can probably do it with a few simple digital
> chips, but thought I would ask...

Use a current source in place of the timing resistor. Then cap
voltage is a linear function of charge time.

Malcolm