2009/12/22 <richard_pr...@att.net>: > What interface do I need for connecting analog drive signal from the PC, and > encoder feedback to the PC? Can this be done directly with just the printer > port, or do I need to get another interface?
You can't do anything analogue from the parallel port, as it is a digital interface. EMC can generate PWM (or PDM) signals, however, which are relatively easy to convert to analogue voltages if that is what your drives need, or can be used to drive the drives directly if they take a PWM input. The simplest PWM to voltage convertor is just a capacitor and resistor in parallel and another resistor to fix the input current. In a closed-loop system it doesn't even need to be all that stable, though the circuit I am using for my spindle speed control adds a precision current source, an opto-isolator and an output buffer for a total part-count of 7 components. EMC can also accept quadrature inputs from incremental encoders directly connected to the parallel port. So, you can sun a servo system directly from the parallel port, and many people have. However: It will tend to not be a very good system. The PWM frequency and Quadrature pulse frequency are set by how fast the real-time threads can run on the PC. A very good latency for a PC would be 10uS or 100kHz. That means that you would be pushing the limits at an encoder rate of 50kHz and a PWM rate of 5kHz. You will also rather quickly run out of pins. As a minimum each axis will need PWM and direction, encoder A, B and Z, and a limit/home input. That's 6 pins per axis. The parallel port has 16 IO lines and they are not individually configurable as input and output. My conclusion would be that you probably need some form of interface card. I am currently using a Mesa 7i43 which connects to the parallel port and provides a configurable number of on-board quadrature counters and pwm/pdm generators. Other pins can be used as general purpose IO up to a total of 48 pins. Other solutions exist, both from Mesa: www.mesanet.com and from Pico Systems: http://pico-systems.com/motion.html There are lots of other suppliers too, but I know that chaps from both those companies are active on this forum and support EMC2. (and are supported by EMC2) As for the last question about the pin-out, that is entirely up to you. HAL gives you total flexibility about what you do with each pin. -- atp ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
