Stepper Driver v1.0

At the beginning of this post I would like to apologise for the time I have not spend doing my homework - on the blog. This post should appear earlier, so lets treat it as being written on the 18th of November, when the actual work has taken place.

The Release Candidate has been presented in the previous post. I have considered the release candidate to be the idea and basis on which the actual stepper driver should be created. The realisation has not been very difficult and time consuming. Please take a look at the pictures below showing the end effect. Lets start with he schema. The circuit has been shown in the third post of this blog. The board with all the wiring is presented below.

Image 1. The circuit on a PCB.

 Some details need to be presented here. First of all lets take a look at the transistors. These are the Q1 to Q6 and all represent the IRF540Z. All resistors are 1kOhm. The J1 represents the power input, so the current that will steer the stepper, the upper pin is the + (24V), lower is the - (0V). The J3 represent the screw terminal which steers the stepper directly, the pins are represented by the stepper inputs, lets match the letters beginning with the left side: UVW. The J2 are the inputs which manipulate the transistor gates. The J2 inputs steer the current from the J1. Lets name the pin headers of the J2 in the following order: {U-, V-, W-, W+, V+, U+} (from the left to the right). This naming tells us that the U+ pin steers the gate of the transistor Q4. The transistor will conduct the current from the + of the J1 to the U output of the screw terminal J3. This is only a half of the normal steering job. there has to be a second transistor which is switched on and will conduct the current to the - of the J1.

So having a circuit I have prepared the wiring for printing.

Image 2. The wiring.

Then I have printed it on a sheet of paper (not a normal one, I suggest a glossy paper, toner transfer paper or a photo paper, or simply try what You have beside the normal paper). Then cut it out and ironed to the clean PCB (see the presented links for more details, I will skip them as they are mentioned everywhere on the net).

Image 3. Printed schema, and the ironed PCB from which
the paper has been carefully removed.

Then I have etched it in Na2S2O8, although You can use the FeCl3 instead (or probably many more too). After that I have cleared the results with the C3H6O. Some while with the drill and the resulting PCB looks perfect.

Image 4. The final PCB.

I don't really know why, but I love to solder. This has been always a difficult task, with which I had many problems. But as I show on the last pictures the outcome looks fabulous.

What is the most important?... Yes, the driver works properly. I will use it the next time when I will present the proposed solution for the reduction of the input pins. Stay tuned.

Prototype and perspectives

After a relatively long time without posts it is time to sum up my actual achievements.

Prototype:

I have created a prototype on a prototyping board.This did not end well, because of my rather old timed soldering equipment, and mainly because of my almost forgotten soldering skills. So although I have managed to create it, and run it a couple of times, it seemed, that there is a cold solder somewhere. So it has not been working as I have expected. After replacing the faulty transistor (my first real suspect, I thought it had burned with my crappy soldering) it went well this time.

Still it is nothing I could be proud of.

Nevertheless I planned to create a Release Candidate, so I bought some things on the net. Modeled the PCB at the beginning using fritzing but the results looked bad (because a lack of functionality that would rearrange my paths orthogonally), at the end using a brute force (Gimp). The results are actually something I can be proud of (Image 1).

Image 1. Stepper driver PCB.

More details concerning the RC version soon :). Actually the description is not needed to fully understand how to solder all elements. The only things I will mention here will be the inputs (lower right part of the board), the current/power (upper left), and the stepper connections (upper middle part).

Perspectives:

The PCB I have imagined will be a module which I want to connect to other modules. The reason for it is the number of inputs I am able to provide for the steering of the stepper. Arduino would most probably not be able to cope with 4 steppers, where each one has 6 inputs because my board does only have 14 of them. So I will try to minimize the driver inputs using the karnaugh method, I predict that out of 6 inputs it will reduce itself to only 4, and adding a counter to it will reduce itself to only 2 per stepper. So it seems to be a lot of fun and hard prototyping work.

Wish me luck.