Hi Roman your stepper pic project sounds very intriguing. I am working on a drive system for a new home project and would love to try out your system for running some 150oz-in steppers. Any chance you would be willing to share your design? I have a 16f84 programmer and am handy enough to build from a schematic and pic listing. regards from the great soggy north ======================================================= Lawrence Glaister VE7IT email: lg@jfm.bc.ca 1462 Madrona Drive http://jfm.bc.ca Nanoose Bay BC Canada V9P 9C9 ======================================================= ----- Original Message ----- From: Roman Black To: Sent: Wednesday, December 27, 2000 5:43 AM Subject: Re: [PIC]: fast easy DAC with PIC > Bob Ammerman wrote: > > > > Roman, > > > > Very impressive idea. > > > > Do I understand correctly: > > > > -- The PWM PIC has no responsibility other than genearating the PWM signals. > > > > How does the PWM PIC know what value to output at any given time? > > > The system was needed for a low cost 8th step > microstepping stepper motor driver. > > I needed to control the current in two phases, > ie two h-bridges, so that is 9 possible current > "sets" of combinations, (9x2 matrix) which can > give all 8 microsteps. I wanted to avoid a hardware > solution as that would eliminate tuning for > torque and degree compensation with large motors. > > The PIC chip (16F84) has 3 pins for the 3 industrial > standard step/direction/enable inputs. It then > drives the 4 halves of the 2 h-bridges directly via > 4 output pins, each through a simple RC integrator. > Using hardcoded PWM loops of differing frequencies > allowed fine tuning of the PWM voltages. I also used > 32 actual PWM settings, to give all 4 quadrants > so there is no phase direction switching needed. > The PIC runs very simple firmware to step forward > or back, and also can select full/half/4/8 steps > via dipswitches. Options include auto current > reduce mode and boost and software anti-resonance > (not really needed with 4 or 8 ustep though!) > > Using 4 PIC pins and 4 RC networks means that I > don't need much external hardware, otherwise it needs > some pins for PWM and others for phase direction > switching. > > The power stage uses hardware current feedback, > so the PIC only provides a reference voltage, the > hardware then adjusts current to match. This is > lightning quick and gives fabulous motor performance > compared to chopper systems that rely on L of the > motor in the feedback loop. > > I have had arguments re the chopper/linear issue > before, but the motor performance of a microstepping > linear driver and a big motor is something else! :o) > > I always use hardware current feedback as it provides > a lot of safety. In the event that the two h-bridge > halves might both be turned on, the whole bridge will > still limit to the correct current. Also will limit > to the correct current if one of the 4 switches in the > h-bridge goes short circuit. > -Roman > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu