From: Scott McDonnell (netsamurai_at_comcast.net)
Date: 2007-04-09 04:25:28
Yeah, Daniel, no can of worms. It just wasn't completely clear what you were looking for. The discussion has just been about methods, one that has been proven to work, and others that should work in theory. Your application is going to require the theoretical solutions, I think. John/Lori (which is it?) I agree an op-amp solution would be great. Of all the analog theory, op-amps are my very weakest point. Any chance you could take the numbers and come up with something? I will see what I can come up with using the transistor and maybe move to FET. The FET should give us more linearity, but I'll have to brush up on my math. The advantage to figuring this out is that the POT inputs could be used for lots of different analog sampling purposes as long as an interface can be made. Of course, some would say it would be better to just have an ADC on the user port. They would be right, but where's the fun in that? :) Anyway, I'm in. Just got to find enough time (and ambition) to work something out. I was getting some crazy ideas yesterday like using an RL circuit with a varying frequency, etc... Mostly interesting just for the academic factor. I should re-install multisim (lets me play with theoretical analog circuits on the computer.) Scott McDonnell -----Original Message----- From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of john/lori Sent: Sunday, April 08, 2007 9:59 PM To: firstname.lastname@example.org Subject: Re: Commodore joystick ports 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 pump. Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing list
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