On Thu, Aug 23, 2007 at 10:40:02AM -0600, Sebastian Kuzminsky wrote: > About the circuit, what is the purpose of resistors R1-R4? They look like > pull-up resistors for the encoder outputs.
The encoder I had used OC drivers, so the resistors were the recommended circuit. If your encoder has push-pull drivers, then the resistor may be inappropriate or unneeded. If in doubt, refer to the documentation for your encoder and follow its recommended circuit design. > I have only a vague understanding of "back EMF" off electric motors. > I believe that the diodes D2-D9 are there to protect the L298 and > the power supply from back EMF. Is that right? How does that work? > (I know, vague question, sorry.) The reasons are exactly the same as for a reverse diode in a simple relay: when the H-bridge switch turns off, the voltage across the inductor rises. The diode allows this voltage to be dumped into the supply rails, limiting the reverse voltage across the switch to a diode drop. The other reason is simply that this is the recommended setup in the L298 datasheet. > If I hook up a power supply to the servo drive circuit, then also connect > the computer's parallel port to the drive circuit, isn't that creating > a giant ground loop? The house wiring ground goes through the computer > power supply, out the parallel port, to the drive circuit ground, which > is also connected to the motor power supply ground, and back to the > house wiring ground. Isn't that bad? Is it something to worry about? > Should there be optical isolation somewhere to interrupt the ground loop? This setup, without isolation or attention to grould looks has worked OK in the etch-servo (though honestly there's no way I will tell if some quadrature transitions were lost, as sloppy as that machine is). It also worked OK for a sherline lathe retrofit, though noise reared its head when using an SSR to switch the spindle motor on and off. That may or may not scale to larger systems with bigger voltages, currents, and noise sources. For a real machine, you want to pay careful attention to grounding and isolation for safety reasons as well as reliability reasons, and I do not have the depth of knowledge to answer those questions well. Jeff ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
