As I mentioned earlier, Chris had already milled a servo control board for his lathe. Like the Etch Servo board, it controls two servo motors with a single L298 chip. Unlike the Etch Servo, it has 3 encoder inputs (X, Z, and spindle). His servo motors have 500-line encoders and have a no-load speed of about 4000 RPM, while the spindle will have a 1024-line encoder with index pulse, but rotate slower (much less than 2000RPM when threading). 133kHz is too fast to count in the PC, but divided by 8 or 16 it's very managable.
mkstate.py is a Python program which generates a quadrature divider table. By changing 'N', 'M', 'x' and 'ux', it's possible to generate tables with different properties. After generating the table, a variety of tests are performed on it to verify that it is correct. Output can be a "C" array or a table of bytes for an assembler program.
qq2.S is a GNU assembler program that actually performs the quadrature division. According to my cycle counting, it polls at 470kHz when a 16MHz crystal is used, so it is expected to work reliably with a 133kHz quadrature signal. So far, though, it has been tested with a single motor spinning at hundreds of RPM.
mkstate.py and qq2.S are released as free software under the terms of the GNU GPL.
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Entry first conceived on 2 June 2006, 18:02 UTC, last modified on 15 January 2012, 3:46 UTC
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