Single Side PCB for Chopper Unipolar Driver
Board Layout
Board Schematic
Parts List (BOM)
Copper for SS PCB (drill aided, sheet of 6)

Mouser BOM for one board (With L297)

If you use the Mouser BOM, the six 2.7K's included substituting the 2.2K's and 1K also. R3, R22, (R16, R17, R18 2.2K) and R2 (1K) I did this since they aren't critical in nature and since there is a minimum order, I just swapped them to all 2.7K's.

About R26, here is the scoop. What power supply voltage will you be supplying to the board? If it's 45V or less put a jumper wire in place of R26, if it higher let me know and I'll figure out what you need. It's more of a just in case option for some.

R6 and R1 are a ratio that set the 5V supply, the schematic calls them out at 720ohms and 240 ohms, they can also be 680 and 220 respectively. R7 and R21 establish LED brightness, they can be any where from 370 to 1000 ohms. Higher ohms value, dimmer but less heat produced by the LM317AHV.

Sense Resistors and Vref.
Vref is adjusted according to the max current of the motor and the value of the current sense resistors. I gave physical room for one to three resistors in parallel for current sense resistors for each coil. R11, R12, (R24) for the out 1 coil, and R13,R14 (R25) for the out2 coil. Depending on the values an number used you come up with a value for the sense resistor. Since both sides are equal, I will just give an example for out1. If one .5 ohm resistor is used in one of the positions of either R11 or R12 or R24 then the sense resistor value is .5 ohms. If two 1 ohm resistors are used then the value is .5 ohm also, just is able to dissipate more heat for higher currents. If three 1 ohm resistors are used the then value is .33 ohms. Parallel resistance is calculated as 1/RT = 1/R11 + 1/R22 (+ 1/R24) if used. First determine the value of your current sense resistance. The voltage you set vref to is = Imax(motor max current) * Rsense(value of sense resistance). So if you have a 1A max current and Rsense is .33 ohm then Vref should be set to .33V. If you have a motor that has a 1.6A max and Rsense is .5 ohm vref s/b equal to .8V.
Prototype 7/15/2005 Click for full size

Updated 4/17/2009