Pololu Electronics

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Pololu Electronics

Release status: Experimental

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Description
Alternative Mendel electronics based on the Arduino Mega and the Pololu A4983
License
GPL v2
Author
Contributors
Based-on
[[]]
Categories
Electronics
CAD Models
Eagle
External Link


Introduction

Under-test.jpg

Note: this design has been tested on the bench, but not yet in an actual RepRap Mendel.

This is an alternative set of electronics for Mendel that is being designed to be as likely as possible for Mendel itself to be able to print.

It is based on the |Arduino Mega and the Pololu A4983 stepper driver.

As Nophead has pointed out, that Pololu driver is a nice design, but with one big shortcoming: it will run hot, and is difficult to cool because it's so small. So what I've done is to design the electronics in such a way that they both perform their function and act as a physical duct for the flow from a fan to direct their own cooling. A happy side-effect of this is that the resulting PCBs are very simple, and can be made single-sided without any thin tracks. That is to say, when we get RepRap making electronics, they will not represent too high a first hurdle.

Indeed, so simple is the design that it is quite straightforward to make it on a couple of pieces of stripboard. That is how I prototyped it.

All the Eagle design files for this are |in the repository here.

Schematic

Pololu-schematic.png

Here is the schematic. The Pololu boards have 16 connections that come out of the edges on a 2.54mm pitch. Those are the twin columns of 8-way connectors shown on the schematic. I deliberately did not design a single device for the Pololu boards, as half their connections go to one PCB, and the other half to the other. The whole thing makes a box structure that both simplifies connections and also ducts the cooling air, as mentioned above.

The Arduino Mega connections are the ones labelled A0, D34 etc.

Making the electronics using stripboard

Components-top.jpg

Here are all the components except the connecting wires. I built it on two pieces of stripboard 13 strips wide by 41 holes long.

Track-breaks.jpg

Here are the reverse sides of the boards, showing the track breaks. It is really important to double check everything at this stage because, after you do the final assembly, it will be very difficult to make corrections.

One-side-soldered.jpg

Solder all the Pololu boards onto one piece of stripboard first, then for the tricky bit...

Tricky-solder.jpg

...you have to reach in with the soldering iron to do the second stripboard. You may find it easier to put the solder in from the other side to the one shown in this photograph.

Pololu-finished.jpg

Simple PCBs

Power-side-pcb.png

Signal-side-pcb.png

I've done a couple of draft PCB designs. They are in the repository. I'll probably change them a bit: it would be convenient if the connections to the Arduino Mega were in the form of one double-row pin header, as that would allow just one ribbon cable to be used for all the signals. It would also be neat to be able to cant the Pololu boards at a slight angle so that one could get a screwdriver in to adjust the current-setting potentiometers more easily. I'll do that when I can figure out how to get Eagle to put things non-orthogonally on a PCB...

Video

Finally, here's a brief video...