Well, I decided to make a flexible prototype PCB (4”x5”) that I will condense once I have tried some stuff because I just couldn’t make up my mind on what I was trying to design here – cheap or robust. I have it set up so I can do unipolar and bipolar type testing. I added AND gates and control outputs that will allow different styles (with some chip replacing and pin lifting). Four different styles of drive are possible for each type. All will use PWM for the microstepping and simple current chopping.
Style 1: Run both coils with simple sinusoidal currents from 0 to max.
Style 2: Run one coil with simple sinusoidal current and the other coil always turned on (sometimes called Hi-Torque).
Style 3: Run both coils as you would a servo or DC motor. That is, each coil always gets max current that is oscillating back and forth to get the sum to be a sinusoidal result. (Does this make sense to anyone else?).
Style 4: Use style 3 but keep one coil always turned on.
(I am rooting for style 3 bipolar).
I’ve received all the parts and sent out for PCBs to be made as I just can not find time to make them myself. I got a new stepper motor rated at 4.6 Amps for current testing, and it has 8 wires to test all the different modes (plus serial and parallel bipolar).
I am starting with a 5volt PIC16F737, but have options to go to the 3.3volt PIC18F45J10 when I get more confident. I am using the free MPLAB toolkit from Microchip and writing in assembly.
I plan to have on-board programming for the chip and I have most of the programmer written in Visual C, so I don’t have to buy a programmer thingy.
I am including my schematic and silk, top, and bottom of the PCB.
Now to find some more free time,
Steve |