At the heart of the module is a Microstepping Driver from Texas Instruments – DRV8825. This DRV8825 microstepping bipolar stepper motor driver is ideal for Nema 17 bipolar stepper motor. It is suitable for 4 wire, 6 wire or 8 wires two-phase hybrid stepper motor if connected appropriately. The module has a pinout and interface that are nearly identical to those of our A4988 stepper motor driver carriers, so it can be used as a higher-performance drop-in replacement for those boards in many applications.
- Simple step and direction control interface
- Six different step resolutions: full-step, half-step, 1/4-step, 1/8-step, 1/16-step, and 1/32-step
- Can interface directly with 3.3 V and 5 V systems
- It operates from 8.2 – 45 V
- Can deliver up to approximately 1.5 A per phase without a heat sink or forced air flow (rated for up to 2.2 A per coil with sufficient additional cooling).
- Over-temperature thermal shutdown, over-current shutdown, and under-voltage lockout
- Exposed solderable ground pad below the driver IC on the bottom of the PCB
- Module size, pinout, and interface match those of our A4988 stepper motor driver carriers in most respects
- Adjustable current control lets you set the maximum current output with a potentiometer, which lets you use voltages above your stepper motor’s rated voltage to achieve higher step rates
- Intelligent chopping control that automatically selects the correct current decay mode (fast decay or slow decay)
- Built-in regulator (no external logic voltage supply needed)
Pinout and Connections
The DRV8825 driver has total 16 pins that interface it to the outside world. The connections are as follows:
Warning: DRV8825 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 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 (preferably 100 µF) electrolytic capacitor across motor power (VMOT) and ground (GND) somewhere close to the board.
Warning: Connecting or disconnecting a stepper motor while the driver is powered can destroy the driver.
The DRV8825 driver has three microstep resolution selector inputs, M0, M1 & M2. By setting appropriate logic levels to these pins we can set the motors to one of the eight step resolutions.
These three microstep selection pins are pulled LOW by internal pull-down resistors, so if we leave them disconnected, the motor will operate in full step mode.
If you need help controlling DRV8825 with Arduino or other microcontroller, you are welcome to contact us.
Setting the correct current
There’s a small trimmer potentiometer on the DRV8825 driver that can be used to set the current limit. You should set the current limit to be at or lower than the current rating of the motor.
You can set the current limit by measuring the voltage (Vref) on the “ref” pin (potentiometer).
- In the datasheet for your stepper motor find a rated current for stepper motor. In our case we are using NEMA 17 with rated current 250mA.
- Put the driver into full-step mode by leaving the three microstep selection pins disconnected.
- Hold the motor at a fixed position by not applying STEP pulses.
- Measure the voltage (Vref) on the metal trimmer pot itself while you adjust it.
- Adjust the Vref voltage using the formula: Vref = Current Limit x 0.5
For example, if your motor is rated for 250mA, you would adjust the reference voltage to 0.125V.