Re: Commodore joystick ports

From: john/lori (
Date: 2007-04-09 03:58:35

Daniel O'Shea wrote:

> I apologise, I wasn't intending to open up such a can of worms!

hey, that's what we're here for, and it's a question that comes
up fairly often.  But I still haven't seen a good answer.
(I still like the PWM idea, but I'd use a 555. haven't tryed it yet though)

> As I 
> stated in my original post, I have a variable voltage of 0 to 5V (no 
> microcontroller involved) that I want to translate in to a variable 
> current using a transistor. And so, I am lead back to my original 
> question - what kind of transistor and what value would work best to 
> provide a variable current which duplicates the potentiometer's variable 
> current? and do I need any extra components besides just a transistor? 
> thanks!

Use an op amp it won't be any more complicated than using transistors by 
themselves and it will be a lot less tricky to get right.

The closest to a single component would probably be an FET.
I believe they make FETs taylored to use as voltage controled resistors.

There's a problem in that any really simple circuit I know of to source
current will (roughly speaking) want a voltage referenced to the
positive supply.  That may or not be a problem, if it is, by the time
you get through taking that into account, you might as well have used
an op amp circuit.

However, it might be tricky getting an op amp current source to work 
with a 5V supply

Another possibility with a 555 would be a V/F converter and a charge

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