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Thread: Wiring question for Teensy 3.2 and DRV8825 stepper driver

  1. #1

    Wiring question for Teensy 3.2 and DRV8825 stepper driver

    I'm planning on using a Teensy 3.2 to drive a Nema 17 stepper (2 amps/1.2 amps per leg) along with several limit switches and LEDs as well as a bluetooth module.

    I'll be using a Lipo 3S battery (11.1v) to drive the stepper. The bluetooth module needs 3.6 to 6v but I've seen several forum threads which say 3.3v works. I also have an LM2596 voltage converter that can up or down convert.

    Several of the schematics for the DRV8825 stepper driver use a 100 uF electrolytic capacitor.

    I have several questions about the wiring:
    1. Can the Teensy and the DRV8825 run from the 11.1v battery and drive all of the modules properly?
    2. Should I use a larger capacitor or multiple capacitors when driving everything from one battery?
    3. Should the On/Off switch go before or after the capacitor?
    4. I'll also be uploading programs with the USB. Will there be a problem having the battery connected during the uploads?

  2. #2
    Senior Member
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    It depends on the battery. For a standardish 2000mAh at 20C = 2A * 20 = 40A continuous draw, which is fine.
    1) Yes. But you should tell us about your battery first to confirm
    2) Yes you'll need big caps to smooth out the current surges the stepper motor puts on the battery. Place them close to the regulator
    3) The on/off switch should go before the capacitors and regulator. Inline with the battery. This is so Off actually is off
    4) This shouldn't be an issue as long as VUSB isn't exceeding 5V. Test with a multimeter before connecting if you're not sure

  3. #3
    Thanks for the quick response. That will simplify the wiring. The battery is a relatively inexpensive ZIPPY Compact 2200mAh 3S 25C from Hobby King.

  4. #4
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    Don't forget a flyback diode for your stepper! Neither your logic or your battery will like any back EMF

    2200mAh * 25C = 55A standard discharge so you'll have plenty of power.
    I'm sure I don't need to remind you to be careful with Lithium-ion batteries though!

  5. #5
    Thanks again. The DRV8825 driver has over current, under voltage, shorts, and temperature protection built in. Is a flyback diode necessary? If so, would I need one for each leg of the motor connected to + and GND?

  6. #6
    Senior Member
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    Nope, you're quite right. The DRV8825 does all of this for you
    Here's a basic setup schematic if you don't have something premade already:
    Click image for larger version. 

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