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Description: The Big Easy Driver, designed by Brian Schmalz, is a stepper motor driver board for bi-polar stepper motors up to 2A/phase. It is based on the Allegro A4988 stepper driver chip. It's the next version of the popular Easy Driver board.

Each Big Easy Driver can drive up to about 2A per phase of a bi-polar stepper motor. It is a chopper microstepping driver which defaults to 16 step microstepping mode. It can take a maximum motor drive voltage of around 35V, and includes on-board 5V/3.3V regulation, so only one supply is necessary. Although this board should be able to run most systems without active cooling, a heatsink is recommended for loads approaching 2A/phase. You can find the recommended heatsink in the related items below.

Note: This product is a collaboration with Brian Schmalz. A portion of each sales goes back to him for product support and continued development.

Note: The silkscreen on these boards HAS been fixed, we are just waiting on updated pics.


  • Bi-polar Microstepping Driver
  • 2A/Phase Max
  • Max Motor Drive Voltage: 35V
  • On-board 5V/3.3V Regulation


Replaces: ROB-11699

Comments 40 comments

  • Note that you can only get about 1.4A/phase out of this driver chip (even though it’s rated for 2A/phase) without actively cooling it and heatsinking it. Even with those, it’s hard to get close to 2A/phase.

    That being said, I’ve yet to find an application where 1.4A/phase wasn’t good enough but 2A was. Normally, for applications where you absolutely need the very maximum torque of your big hoss motor, you’re going to opt for much more robust and powerful drivers like Geckos.

    Also note that you can’t damage this board by over heating it. (This is not a challenge. ) The driver and voltage regulator have built-in over-temp circuits that will cut out their outputs if they get too hot. You’ll notice that the motor will start to ‘stutter’ if the chip gets too hot. Just back off the current adjustment pot in this case to send less current to the motor.

    Some users have trouble getting smooth microsteps. I always tell them to start with a nice slow pulse rate - maybe 10Hz or lower, and feel the shaft of the motor with their fingers as it’s rotating. At 16x microsteps, you may feel there are some steps that are more or less powerful than others. Adjust the current limit pot, or increase the input voltage, if you have trouble getting smooth micosteps.

    Also note that if the coil resistance of the motor you have chosen is too high, the BED can’t create microsteps properly. If you raise the input voltage, that will help solve this problem. Or just use a motor with lower coil resistance.

    Under normal usage, this driver can push a substantial amount of current through the motor - especially when it’s not moving. The motor can and will get quite hot. I’ve not burned myself on a motor (yet) but I’ve gotten close. Be careful. Even at 1A/phase @12V, you’re dissipating 24W in that motor.

    The amount of current you see being drawn through your power supply is NOT the same as the current going through the motor coils during motion. So if you’re stepping, and you see 500mA being drawn from your 24V power supply, that does not mean that each coil is getting 250mA. You have to measure the TP3 test point with a meter, and use the formula in the data sheet to figure out the actual maximum current through each coil. Typically the current through the coil will be much higher than the current drawn from the power supply because of the chopper circuit on the BED.


    • What would happen if I connect 2 steppers by joining coils in parallel? I need 2 steppers to be perfectly synchronized.

      • You can try that. And depending on the coil resistance of your motors, the torque you need, and your input voltage, it may work. However, that will present a lower coil resistance to the driver board, which may or may not be a problem.

        Another way to do it is simply take two BEDs, have each one power a motor, and run the same step/dir lines to both drivers. I’ve used this before to ‘gang’ any number of stepper motors.

  • I’m using BED and I’m very exciting with works. You can see photos and videos of first test at

    So, now I need to more speed. My “leadscrew” has 1,5mm pass per revolution of motor.

    I’m using a 12V power supply, and default BED with no jumper configuration. I mean, I guess the BED is in 1/16 microstepping by default.

    I will use now a 24V power suply. My question is: I have to put the BED in full stepp mode to get more speed?

    And if yes, how I do this? It’s just jumper the MD1-3 to GND? Or I have to cut of some trail of the board. I have no ideia to how chance between High and Low the MD1, MD2 and MD3 pins, because, I think the BED in default is in High, so, if I connect the MD# pins to GND to put them LOW, I will make some thing wrong?

    Sorry my english.

  • Hi,

    my big easy driver recently stopped working. When i measure the signal on the motor outputs i just get the same voltage as the powersupply (5V) even though i have the stepper and direction as well as ground inputs connected.

    shouldnt i get some rectangular signal from the motor outputs?

    Now the outputs A,A',B,B' are all 5V if powersupply is turned on and 0V if turned of. Is this a sign of a burnt chip`?

    • It could be. Do the Q13) checks on and see if you have any errors there. That should help you determine if you have a bad driver chip or not.

  • Hi all,

    Has anyone had a problem reversing direction when in any of the microstep modes? I can change direction without problems in full step mode, but any time I run in microstep mode I cannot get the motor to change direction, regardless of setting the direction pin high or low. It always runs as if the direction pin is high. Any ideas or suggestions please?

    • I have seen a couple of people with this problem in the past. Sometimes it’s a problem with their Arduino code (check your DIR pin with a volt meter or scope to make sure it’s going all the way high and low) or grounding between the various pieces of the system.

  • Just a quick question -

    I am going to be using the PRT-11510 Small Heatsink. Where should I place it? On the top or on the bottom where all the thermal pads and vias are? It seems to me that with this design the bottom would be better.

    Regards JohnK

    • You can heatsink the driver chip on the top of the board, or you can heatsink the boar itself on the bottom of the board. Putting the heatsink on the driver chip itself will allow you get more heat off of the chip (since you’re not going through the board), but if you have a large metal surface that you can attach the board to (with a properly electrically insulating thermal pad between) you may get even better dissipation.

  • I see a few of these have been blown. Looking at the data sheet the equation for max current is I_max = V_ref / (8*R_s).

    The board schematic and features list say the current adjust pot will give you 0 to 2.4 Amps.

    However, if using the board at 5V logic level I get the max current to be 4.5 amps since you can put a max of 4V on the V_ref pin (unless the adjustment pot is limited) and the R_s resistors are 0.11 ohms. Now I’m sure it can’t actually do 4.5 amps, but it’s definitely allowing it to run completely maxed if not over-run.

    On the website the old version 1.1 has R_s values of .22 ohms and you can put up to 4.2V on V_ref. This setup works out to exactly 2.4 amps.

    What am I missing? Why the change?

    • The resistor change was due to the need for reducing the power and voltage lost across the sense resistor. The smaller that sense resistor value, the more power goes into the motor, and the better we can make the microsteps at a lower input voltage. You are correct - if you crank the pot up high it will try to tell the driver to use more current than it’s able to dissipate. What happens in this situation is simply thermal limiting - the driver chip rapidly cycles on and off, which will keep it’s die temp down, and will produce a chattering or stuttering of the motor. This protects the driver chip. So you can’t hurt the driver by turning the pot up too much. Note that the actual max current you can get will depend on your input voltage, current pot setting, motor coil winding and inductance and ability to remove heat from the board. So some people max out at 1.5A, and some max out at 2.4V or above.

      • Do we know why the Vref resistors weren’t updated to match the new Vsense resistors? What’s the point of having over half of the pot’s range have no effect on Imax? And why does the schematic say you can adjust the current limit from 0-2.4A when the chip only claims to be able to provide 2A?

        • Cheese - you have good points. The resistors for Vref should be tweaked to give a better range. The notes on the schematic should be changed and amended to better explain how adjusting the pot controls the current. There are a lot of subtleties to this though that can’t really be completely explained on the schematic and are, unfortunately, left up to the user to understand. For example, just because you set the pot at 1.5A doesn’t mean you’re going to get 1.5A/phase. It also depends on the inductance and resistance of the motor coil, as well as the input voltage to the BED. It will never be more than 1.5A if you set it there, but it may be less.

          SparkFun has begin using Github to manage design files (which is totally awesome) and I will work on updating the schematic at the very least to better explain. Thanks for the suggestion.

          • Okay cool. In the meantime, I posted a separate comment explaining how to set the max current so that people don’t have to bother thinking about it too much unless they feel like it.

  • I’ve blown two of these boards. Anytime the motor stalls. I’ve used fast blow fuses on the motor wires, the power input, pretty much anything I can think of. I will not be buying a third. For $10 more you can get the SideStep from Probotix. They use the much larger Allegro chip. That chip is what most CNC’s controllers use unless they spring for discrete electronic boards like the geckos. I wouldn’t use this for anything serious.

    • I’m really sorry to hear you had problems with the BED. It sounds like it’s best that you try other boards to see if you can get your system to work. Many people have constructed CNC systems using BEDs with no problems in the past- I’m very confident in the design itself. These little Allegro chips are quite sturdy. But because of the big powers involved, it is easy to make an innocent mistakes that can cause damage to the driver.

  • guys im still having a hell of a time getting this driver to drive…

    I was able to get the motor to step using a ULN2003AN connected to my arduino but when i use the BED all i get is studdering back and forth… Every once in awhile it will drive one way then sporadically change direction..

    Ive tried two different power DC supply’s.. One 12V @ .5A and 30V @ 1A and i get the same results with both…

    Ive double and triple checked my wiring config and its correct..

    Ive adjusted the POT with no avail.

    I connect pairs A to A pairs B to B and leave the center coils disconnected.

    Ive tried every stepping mode the board offers and the default 1/16 microstepping mode is the only one that gets close to operating the stepper

    Ive used several different librarys including the AccelStepper to no avail..

    the stepper im using is a Japan Service Co. KH42JM2 NEMA 17 series stepper… Its rated for roughly 4.95V @ .85A in bi-polar config and ive read over and over that 12V @ 0.5A should be sufficient and that you can over volt the crap out of steppers..

    I also tried a stepper out of an old printer and again, the same results.

    Can anyone offer any assistance? What am i missing here?

    Motor Datasheet:

  • Uh yep… Mine fried as well…. Bought another one but it appears that was a mistake and a waste of another 24.00… This thing is junk… Take the advice of the developer himself and go with a Gecko driver…

    • Yeah, the Big Easy Driver and the Gecko are in completely different worlds. Not only are their prices very different, but the Gecko can drive much larger motors much faster and much more smoothly than any little Allegro based solution like the BED. Totally different class. If you need to move big motors, don’t use a BED, you’ll be disappointed. If you need to move NEMA 17s or some of the smaller NEMA 23s, this should work out just fine. I’m really sorry that your BEDs died - but in almost every case that people have brought to my attention, some type of user error or mistake was found that likely caused the problem, not a bad board from SparkFun.

    • They are pretty reilable, but if you have an instance where you NEED a geckodrive, the easy driver probably isn’t the right product for you anyways. This is made for smaller steppers with limited current. geckodrives do have a LOT more protection, but most of the time you don’t need it. plus, a geckodrive is $120+. apples to oranges.

  • Hi I bought 2 of these little guys to driver two 125 Oz in. I bought here also. After wiring them up I ran the example code from Bildr tutorial and i got it to move but it was kind of jerky so in an attempt to get it to run smoothly I turned the current adjusting pot one way and the other and suddenly the horror! Magic smoke all over the place! i even saw a glow on the little BED! This happend to both my circuits :( Im kind of new on driving stepper motors so any help as how can I set up the correct amount of current from the pot will be very much appreciated.

    I was supplying 12V the first time and 20V the second. Im looking for the max torque i can get from the stepper.


    • Sorry to hear you are having problems with your set up! I recommend contacting techsupport@sparkfun and walking through your set up with them. Because the motors you were using are unipolar, it’ll be important to ensure you have everything hooked up properly. They’ll be able to help you out with all of that better than we can in the comments.

  • Just to save people some work, here’s how to set the max motor current:

    Vref = 8 x Rs x Imax = .88 x Imax

    Rref = 8 x Rs x Imax x Rtot / Vdd = 2.1982 x Imax


    • Imax = desired max motor current
    • Vdd = logic supply voltage = 5 V
    • Vref = voltage on REF pin, set by the voltage dividing pot
    • Rs = sensing resistor = .11 ohm
    • Rref = resistance on the low side of the pot wiper
    • Rtot = total resistance of full pot plus limiting resistor = 12.49 kohm

    For your convenience, here’s a table of values based on the current board design and Vdd = 5 V, in 0.25 A increments:

    Imax    Vref    Rref (k ohm)
    0       0       0
    0.25    0.22    0.55
    0.5     0.44    1.1
    0.75    0.66    1.65
    1       0.88    2.2
    1.25    1.1     2.75
    1.5     1.32    3.3
    1.75    1.54    3.85
    2       1.76    4.4
  • I can’t get the BED to run my stepper motor :/. I conneted everything the same like in this tutorial but the only thing my stepper is doing, ist stepping one step clockwise and one counterclockwise. My PSU has 12 V /1,5A. The stepper is a NEMA 17 rated with 12V / 0,4A. I also tried it with a more powerful PSU rated @ 24V /2.7A an a 24V stepper with 1A but still the same problem.

    Can someone help me out here :) ?

  • I’ve noticed a few comments here lately from people who had trouble with the BED. Therefore, I am going to add my experience to the official record. I bought two BED’s in the past 3 months (about a month apart.) One of them worked perfectly, but the other behaved much like those described in posts below: choppy, inconsistent motion. Note that I have been able to precisely compare the two BED’s with the exact same motor and hook-up (NEMA 23, 1A and 7.4V per phase). Just prior to my posting this, the defective board went up in flames (literally). To whomever it may concern, it might be time to investigate whether a particular batch of BED’s is flawed.

  • Hi

    im thinking of building myself an arduino controled CNC machine to learn some new things (and end up with an usefull tool for future projects ;P) but im wondering if its possible to connect 3 of these to an arduino to control my XYZ axis and if yes how? i cant seem to find a schematic for it online…

  • Would anyone know what the best rotary encoder is to use with this driver?

  • Hi,

    I recently buy this driver, with a NEMA 23 stepper motor, and with Arduino, I have tried to move it, but I can not. I have used a circuit similar to reprap 3d printer (Arduino controls ENABLE, DIR and STEP) and the other pins are fixed, but the motor does not move. I have noticed that the voltage regulator, it is heated up, so I think this component is damaged. Is there any way to check I am correct? Are there other explains? What is exactly the voltage regulator for replace it?

    Thank you very much, Antonio.

  • has any one connected any screw terminals or does every just solder header pins to this board ? thanks

    • Yes, I’ve seen many people solder in the 3.5mm pitch screw terminals. They work great. I’ve also done it a lot too.

  • In the description, it says “maximum motor drive voltage of around 35V”. Unfortunately the only affordable switching power supply I could find are 36v. Do you think it could handle it?

    • Unfortunately, the A4988 driver chip has a maximum voltage of 35V. Using 36V might work, but you would be beyond the ‘absolute maximum rating’ as per the datasheet.

  • Cool that Brian is actively commenting here. Thanks!

    This looks like a great board. Wish there was a breakout or adapter that allowed it to plug and play with the Polulu sockets commonly found on RAMPS and other reprap boards. More options the better!


    • Unfortunately the board sizes are quit different. If I made a version of the BED that could fit into one of the Polou pinouts, you couldn’t have them as close together as many of the RAMPS boards do. Sorry-

  • I am attempting to drive a Karlsson 267 oz-in Stepper Motor using a Allen Bradley PLC to drive an automated book scanner system. The stepper is rated for 2.8A (I thought this meant 1.4A/phase, which made the BED an option). The PLC has 24V transistor outputs hooked to STEP, DIR, and GND. I used a voltage divider of R1 = 1.5M and R2 = 330k to yield V input = 4.34 V and I input = 16uA to meet the specs per the A4988 datasheet so I don’t see the PLC being the issue. M+ is hooked to a 24VDC power supply.

    When I first ran the program, the BED was fine and the stepper was making sound but did not step. Per the directions in the user manual, my next step was to adjust the current pot. I used a multimeter to GND and TP1 to get reach a Vref = 1.76, to reach the max 2A. The stepper started to sound closer and closer to actually stepping as I turned the current up. During the process of adjusting the pot, the board turned off. I assumed it got too hot and the voltage regulator temporarily shut it down. Now every time I power up the board, I hear a quick pop, the LED go bright and depending how long it has been sitting, it dims out and board is off - this usually takes between 1-3 seconds after power up. The component nearest the motor pins gets very hot if I leave the power supply turned on to the board. The board quickly turns off regardless of where the pot is set.

    Is this board fried or is it overheating? How do I correct this issue? Heatsink?

    Is the board compatible with my stepper or do I need a different driver board? If I need something else, is the Probotix SideStep driver a compatible board for my application?

    Any and all replies are gladly appreciated, I am very ready to solve my stepper woes.

    EmbeddedMan PLEASE HELP.

    Here is the link for my stepper:

    • It sounds like your motors are compatible - however you won’t be able to get anywhere near the fully rated torque out of them with the BED. That may or may not be a big issue depending on exactly how you’re using them. The 2.8A means 2.8A/phase.

      Have you measured the maximum HIGH voltage on the STEP and DIR pins from your PLC? If they are over 5V, then they may have damaged the BED. Your resistors should have prevented that problem, but measuring it (without the BED in place) would be a good double check.

      if you disconnect your motor from the BED and then power up the BED, do you still see the same LED pattern?

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