Cutstom Tool. Extruder Protocol Question

Hi,

I am looking to switch the extruder in my reprap out for another tool. I want to be able to turn my new tool on and off, but no other controls are necessary. I can not use a modified extruder controller board.

Where Can I find information about how the reprap motherboard v1.2 (http://www.reprap.org/wiki/Motherboard_1.2) communicates with the extruder or with a tool?
Does anyone have advice about how I can do this?

Thanks.

Actually, it may be easier to use the extruder controler. Especially if you already have one. Driving it with the motherboard directly will require custom firmware coding in addition to custom wiring.

The motor driver chips should output a full 12V if you set the speed for that "tool" to 255. As a device intended to drive motors, I would expect that it could easily handle switching the coil on a relay. Then all you have to do to control your custom tool is turn on and off the "extruder" and it will turn the relay on or off, which in turn controls your tool.

With this arrangement, it will not matter what voltage or amperage your tool needs. You just need to make sure the relay contacts are rated to handle it. If you need it to switch quite frequently (IE 50 times per hour), consider using a solid state relay instead.

That would probably work, but I don't have an extruder controller and I wont really want to buy a full board for my simple on/off task.

What sort of signals are being sent to the extruder controller?

It uses RS232 communications. Since it isn't just an on or off type of output, you would probably be better off adding your own firmware code so that M127 and M126 toggles a pin on the motherboard.Then you can use the machine codes that normally run a valve to control your tool.

As far as hardware goes, you would need a mosfet or similar with a gate saturation voltage of not more than 5V. Finding one of these with an output suitable to your custom tool might be expensive and hard to find. You might get away with a 5V relay, but you should use a reverse biased diode to protect your output pin. Some relays might draw too much current too. I'm not sure what kind of load an output can drive.

I would forget about trying to intercept communication from the extruder controller port because this will either require an extra micro controller or heavily modified firmware.

Hi,

What about hijacking an unused motor controller port? Does anyone see a possibility here?

I would need to be able to control the 'enable' and 'dir' bits directly from G-Code. Do you think that is possible?

-Evan

I don't see Gcodes for that in the RepRapGCodes list, but it should be possible to add them. Depending on how often you want to switch it that could be little more than a minor inconvenience. In fact, if you just wanted it on at the start and off at the end, you could put it in skeinforge's start and end Gcode preface files. Skeinforge would automatically add the commands then. Getting more than that out of any slicing program is going to be tricky and/or impossible though since it will not be a normal reprap code.

I guess you could also spoof the firmware into using M127/M126 to do it, which would make it simpler. Whatever you do, I'm thinking you should probably use M126/127 as your control codes because these are already designated as on/off type control codes. Slicing programs written for reprap should have the ability to use them. I doubt you will be able to do this without some amount of custom firmware code - especially not without an extruder controler.

An old trick we used on dummy NC machines was to fit a switch on the corner of the bed and programme the movements so a striker on the head operated the switch.

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Regards

Ian