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Newsgroups: comp.sys.apple2 Path: news.uiowa.edu!chi-news.cic.net!newsfeed.internetmci.com!news.msfc.nasa.gov!elroy.jpl.nasa.gov!usc!news.cerf.net!nntp-server.caltech.edu!news.ridgecrest.ca.us!owens!croton From: Cyrus Roton <croton@ridgecrest.ca.us> Subject: versatile interface X-Sender: croton@owens X-Nntp-Posting-Host: owens Content-Type: TEXT/PLAIN; charset=US-ASCII Message-ID: <Pine.SUN.3.91.951025104138.7395A-100000@owens> Sender: usenet@ridgecrest.ca.us (Ridgenet Usenet admin) Organization: RidgeNet - SLIP/PPP Internet, Ridgecrest, CA. (619) 371-3501 Mime-Version: 1.0 Date: Wed, 25 Oct 1995 17:44:56 GMT Lines: 71 GAME PORT, VERSATILE INTERFACE A multitude of interface cards exist for the Apple II But, few people realize that the Apple II game port can be a very versatile interface. A "paddle" input is internally connected to a trigger chip and a .022 MFD capacitor. The paddle is a variable resistor and a voltage source. In use, the capacitor is discharged, a timer (counter) is reset, and then the capacitor is allowed to charge by current passing through the external resistor while the counter is incrementing. When the charge on the capacitor reaches 3.2 volts, the trigger circuit stops the counter. The number stored in the counter at that time gives an indication of the time required for the capacitor to charge up to the trigger voltage, and that time relates the value of the external resistor (paddle) as follows; V = (input voltage)*(1-EXP(-t/R*C)) From experiment, we find that with a 5 volt input and a 120K resistor, the counter will reach a value of 250. From this fact, and using the above formula, we can plot the count as a function of resistance Knowing all of this, we can design interface circuits. Such devices as photocells, photo resistors, thermisters, and other things could be connected to the game port. With appropriate software, we could use the Apple to monitor a variety of real-world events, and to display the results. For example, a local chemistry lab wanted to measure the "time of solution" when a chemical was dropped into a test tube containing a solvent. The solvent was clear, but changed color when the chemical dissolved into it. A light was passed through the test tube to strike a photo resistor. A TYPE 7 photo resistor, which has peak sensitivity with orange light, varies its resistance as a function of light intensity, with the formula R = (443)*(I^(-0.6692)) where R is in Kilohms and I is in foot-candles. Futhermore, the minimum sensitivity of the photo resistor is with violet light, which happens to be the color when thiothymolyne is dissolved in water. When the photo resistor is connected to the paddle input with 33 volt source, the resistance in Megohm is calculated by the approximation; R = (count)/209.9 The point of all this was an attempt to refute the results obtained by Prof. Azimov, as reported in April 1948. The Prof. had reported that thiothymolyne displays a negative "time of solution" when dropped into water. Prof. Azimov may have been correct. Unfortunately, meaningful results could not be obtained from the above experiment because the Apple II is too slow to measure negative time. Perhaps one of the new optical computers, which operates at the speed of light, could be fitted with an accelerator to operate faster than light, and thus be used to measure negative time. Of course, some of this is in jest. But such interfaces are practical, within the limitations of the Apple II game port. Cyrus Roton croton@ridgecrest.ca.us Ridgecrest Apple User Group