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maximum voltage rating for the DRV8825 and permanently damage the board, even
when the motor supply voltage is as low as 12 V. One way to protect the driver from
such spikes is to put a large (at least 47 µF) electrolytic capacitor across motor power
(VMOT) and ground somewhere close to the board.
MOTOR CONNECTIONS
Four, six, and eight-wire stepper motors can be driven by the DRV8825 if they are
properly connected; a FAQ answer explains the proper wirings in detail.
Warning: Connecting or disconnecting a stepper motor while the driver is powered
can destroy the driver. (More generally, rewiring anything while it is powered is asking
for trouble.)
STEP (AND MICROSTEP) SIZE
Stepper motors typically have a step size specification (e.g. 1.8° or 200 steps per
revolution), which applies to full steps. A microstepping driver such as the DRV8825
allows higher resolutions by allowing intermediate step locations, which are achieved
by energizing the coils with intermediate current levels. For instance, driving a motor
in quarter-step mode will give the 200-step-per-revolution motor 800 microsteps per
revolution by using four different current levels.
The resolution (step size) selector inputs (MODE0, MODE1, and MODE2) enable
selection from the six step resolutions according to the table below. All three selector
inputs have internal 100kΩ pull-down resistors, so leaving these three microstep
selection pins disconnected results in full-step mode. For the microstep modes to
function correctly, the current limit must be set low enough (see below) so that current
limiting gets engaged. Otherwise, the intermediate current levels will not be correctly
maintained, and the motor will skip microsteps.
