From: Scott McDonnell (netsamurai_at_comcast.net)
Date: 2007-04-07 18:48:22
Pasi, You make a good argument and one I had thought of as well when I second-guessed myself this time. So, now I am confused again, thanks! :) Perhaps the simplest way to know for sure would be to just try it. Just keep in mind two things and no damage should result: First, make sure your grounds are very well connected together. Second, make sure your voltage will not exceed 5.1V. This should prevent any damage, but it either will or will not work. Make sure the resolution is correct, since you will get "something" regardless. If it works flawlessly, you should have a resolution of about 20mV per count (5V/256 discrete values.) I still have some strong reasons to believe it will not, but I have been working solely on digital & microprocessor circuitry for so long now, my analog is getting a bit fuzzy and I don't fully recall my tests at the time. At the time I wrote that original post, I was working on recreating the SID in discrete circuitry at college. I got pretty far into it, but never finished it. I was using a 555 timer for the paddle input. Maybe my logic was skewed at the time for that reason. Obviously, it would be desirable if the voltage can be inserted directly. If it does not work, I will continue to flesh out the circuit needed. I don't have a set up to test it either way at the moment (my commodores and my college notes are packed away right now) so someone else will have to physically try it. Scott McDonnell -----Original Message----- From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Pasi Ojala Sent: Saturday, April 07, 2007 4:57 AM To: email@example.com Subject: Re: Commodore joystick ports > I have a variable voltage of 0 to 5V, and I want to > translate this in to a current to simulate the variable resistance of a > potentiometer connected to the SID's ADC I'm almost certain the SID input isn't a current-input, and the AD would work just fine by simply connecting the varible voltage directly. (My hazy recollection is that I once tried to use the SID ADC's for audio sampling, but obviously they are just too slow.) To make the actual conversion, SID samples the input by charging a capacitor, and then discharges it through a resistor. The amount of time it took gives the conversion result. At least that's what I remember reading (from Programmer's Ref.Guide, probably) 20 years ago. Because the input impedance limits the draw current, and sampling really takes place (the sample capacitor is not charged continuously), you really should not be forced to emulate a variable-current drive. To think about it in another way, the input impedance provides the voltage division even if the potentiometer does not have the center pin connected. Or am I mistaken? -Pasi -- "Khrm." "It's .. animal magnetism, what can I say?" -- Londo and G'Kar in Babylon 5:"A Tragedy of Telepaths" Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing list
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