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POLOLU DRV8825 STEPPER MOTOR DRIVER
CARRIER, HIGH CURRENT
USER’S GUIDE
USING THE DRIVER
Minimal wiring diagram for connecting a microcontroller to a
DRV8824/DRV8825 stepper motor driver carrier (full-step mode).
POWER CONNECTIONS
The driver requires a motor supply voltage of 8.2 – 45 V to be connected across
VMOT and GND. This supply should have appropriate decoupling capacitors close to
the board, and it should be capable of delivering the expected stepper motor current.
Warning: This carrier board uses low-ESR ceramic capacitors, which makes it
susceptible to destructive LC voltage spikes, especially when using power leads longer
than a few inches. Under the right conditions, these spikes can exceed the 45 V
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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.
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MODE0
MODE1
MODE2
Microstep Resolution
Low
Low
Low
Full step
High
Low
Low
Half step
Low
High
Low
1/4 step
High
High
Low
1/8 step
Low
Low
High
1/16 step
High
Low
High
1/32 step
Low
High
High
1/32 step
High
High
High
1/32 step
CONTROL INPUTS
Each pulse to the STEP input corresponds to one microstep of the stepper motor in the
direction selected by the DIR pin. These inputs are both pulled low by default through
internal 100kΩ pull-down resistors. If you just want rotation in a single direction, you
can leave DIR disconnected.
The chip has three different inputs for controlling its power states: RESET, SLEEP,
and ENBL. For details about these power states, see the datasheet. Please note that the
driver pulls the SLEEP pin low through an internal 1MΩ pull-down resistor, and it pulls
the RESET and ENBL pins low through internal 100kΩ pull-down resistors. These
default RESET and SLEEP states are ones that prevent the driver from operating; both
of these pins must be high to enable the driver (they can be connected directly to a
logic “high” voltage between 2.2 and 5.25 V, or they can be dynamically controlled via
connections to digital outputs of an MCU). The default state of the ENBL pin is to enable
the driver, so this pin can be left disconnected.
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