froncio@caip.rutgers.edu (Andy Froncioni) (06/26/91)
I am looking to perform slow A-to-D conversion from an ibm-pc/at game port. I've managed to sort-of figure out what's going on with game port: The game port is simply a dual 555-timer circuit whose running in astable mode. The pulse frequency is controlled by an RC circuit pinned up to +5v. The R of the RC circuit is provided by the joystick potentiometer. The value of a joystick coordinate is obtained by polling the pulses and returning the value of a counter that times interval between the pulses. What I'd like to do is to trick the 555 timer into changing its pulse frequency by pinning the RC circuit up to the analog signal instead of +5v. That way, the charge-up time of the capacitor is modulated only by the analog voltage. I've had mild success, but I'm tired of playing around with ressitor values and zero offsets. Has anyone out there done this? What's a good, solid set-up to take an analog voltage between 0 - 5v and convert it to a number between 0 - 255? Someone must've done this before..... Thanks, Andy -- Andy Froncioni CAIP Center Parallel Computing Lab froncio@caip.rutgers.edu Rutgers University, Piscataway, NJ