Help on 3 Axis Stepper Controller





Introduction: Help on 3 Axis Stepper Controller

Hi, iḿ new to this DIY but iǘe built some of instructables stuff before, now i'm trying to build a 3 axis cnc. Found this simple controller to be connected to lpt port, but I need help identifying the three legged parts on the middle of the circuit, are those npn's? Resistors? What are thoe, can anyone point me out?



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    I swear I saw this in an instructable somewhere (in addition to the makeyourbot site), does anyone know which one its from? I want to know how to set up software for it.

    This links to a .pdf that gives a better parts list. It's in French but for your question is OK.

    Those are Opto couplers. In CNC you should divide the parallel port from the actual motors (EMF risk). From the picture, this is surely a BOB (break out board). From the BOB you connect the drivers for the motors and as far as I can see the pin 1 of the DB25 connector is connected to the Z axis, so I would assume the BOB is designed for ULN2803 Darlington drivers. These drivers are rated at 0.5A and people use them in parallel to increase the current to almost double (1A approximately). If you would like to use these cheap drivers, go here:
    Or just search the “ULN2803 stepper”

    7 replies

    can't be opto couplers. optocouplers have 4 or more pins (2 for LED, 2 for transistor).

    can't be resistors and capacitors either (they are different shape and have 2 terminals). btw. you do have one resistor in the lower corner of the board between mount and pins of DB connector.

    the 3-terminal devices can be diodes, transistors or ICs.

    it is not likely to be diodes (unless parallel port is used to read signals).

    if the parallel port is used to drive loads (stepper motor for example) then those must be transistors.

    this is a "brute force" stepper driver. As I can tell it is a direct connect from the parrallel port to the steppers.

    you can find this driver on makeyourbot dot org

    Brute force meaning that it has no logic in place to prevent the mechanisms from stripping if it hits a physical limitation? I'm just starting to look at stepper motors for a project and haven't come across this term yet.

    this term is from MIT makeyourbot. I have only found 1 other person on the internet talk about, the brute stepper driver is asked about on cnczone. I emailed the guy who created the driver/board, but have not heard anything back.

    More like it uses the brute force of your computer to generate the step sequence. These are the lowest performance drivers going unless you have a very powerful computer. Better to off load the sequencing to the motor driver and just send it step and direction inputs.

    Thank you very much.

    thanks a lot 4 everyone that replied, iĺl post some news as soon as i get it working.

    wow.... Best of luck....

    those are

    N-Channel Logic Level Enhancement Mode Field Effect Transistor

    makeyourbot dot org

    Well, I'm an electronics tech thats been dealing with smd's for few years now. I can tell you those in your pic could be either transistors or diodes, but they are NOT anything else. There are some alpha/numerics imprinted on the face of the device. If you had the right info you could determine exactly what they are. First thought was that they were diode in nature, but then I noted the resistor @ low center of the pic. I see the resistor tied to several pins tied together; possible ground. The big trace is coming out and turning under each SMD. I am assuming that it is connecting to each right side leg of the SMD that otherwise appears to be going no where. So, now I am assumming that they are switching voltage and shunting it to ground. Now whether they are npn, pnp, or fet all depends on what the design that was being followed. But, I might think they are fets to handle current.

    Yup, those appear to be transistors.

    That's the beautiful thing about SMD and today's technology, you can have an equally powerful device in a fraction of the size.

    I would assume it's just a unipolar driver. However, I can say that using SMD isn't really necessary and with stepper drivers I personally believe it's better to use DIP sockets with DIP IC's. This helps with maintenance in my opinion, unless of course you absolutely know what you're doing and trust the DIYer to understand just as much when matching the board to motor.

    2 replies

    Thanks, i think it´s easier going with the uln2803 version first, dealing with smd it´s a little too much for me yet.

    Yeah, that's another benefit of using through-hole.

    Best of luck.