Originally Posted by katti Then there is third, more complex and expensive solution that is
still better than analog conversion. Make FPGA based PCI board
using www.opencores.org PCI core, implement encoder input and
SPI output for motor command. So, replacing DA->AD just simple
SPI. There is also possibility still interface encoder to microcontroller
and then use same SPI to read encoder position back. |
this would be the most interesting option I think.
There's an FPGA card sold by mesa electronics (
www.mesanet.com) called "5I20 FPGA based PCI Anything I/O card " which sells for $199.
It has a 200kgate FPGA and 72 general purpose I/O pins
It will probably be hard to come to this price range for a DIY design - or it would require production of 100s of boards.
There's an FPGA configuration for the 5i20 that has an EMC2 driver. it's called HOSTMOT-4. It provides 4 "analog" outputs and up to 8 encoder counters + about 24+16 bit general purpose I/O.
the "analog" output for controlling a motor consists of a direction pin and a PWM output pin.
The FPGA code in VHDL format is opensource and can be found in the EMC2 CVS.
I emailed the guy who works at Mesa electronics who wrote the fpga configuration and he confirmed that they had also tried direct control of BLDC or 3-phase AC motors with the FPGA.
One problem is that direct control requires lots and lots of pins. For 3-phase H-bridge driver you need 6 outputs. Then something for detecting the phase currents etc.
Still, I think it would be a nice way to do motor control. Have all the "smart" bits of the control in FPGA/VHDL meaning they can be reconfigured anytime someone finds a way to improve the code.
The power electronics would be "dumb" powerstages + current sensing amplifiers (IR2175 provides current sensing with PWM output, suitable for a digital-input-only solution).
If I would be competent in VHDL I would probably pursue this option further right away but unfortunately I think I don't have time to learn VHDL right now...
I understand the Xilinx compiler needed to compile the VHDL for the FPGA is available freely from Xilinx.
AW
PS. At work we have national instruments FPGA cards which can be programmed with LabView - soo much easier than VHDL. Well they cost about 3-5k /card + software ....