This IC can be considered something in the middle of Allegro-Sanken line for unipolar stepper motors. Probably it is the easier to find on the market. It is really interesting because it's internal circuitry provide a current limiter after a short period of time (around 10 secs) of inactivity.
As usual: microstepping (up to 1/16), 3A of current/phase, 44V max. The circuitry is quite simple (and the pcb as been studied to be milled easily) and follows the traditional style of the maker:
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In the schematics have been used two resistor of .5 ohm but any resistor between 0.2-2ohms will be fine remembering that the current for any phase of the motor is given by:
I=Vref/Rs (with Vref >.1V and <2V). The reset has been disabled, useless in a normal use, and the enable pin managed by a small mosfet.
The dip-switch can be replaced by small bridges. here follows the table of steppings:
M1 M2 (pins of the IC)
H H half step
H L quarter step
L H eight step
L L sixteenth step