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Tommelise 3.0 I2C board finally builtSaturday, June 06. 2009In which your narrator turns designs into hardware with remarkably little trouble... Some time ago, I built up an I2C stepper controller board which can control two steppers to run my IR ranging scanner. This project allowed me to test out the viability of using I2C comms with I2C slave chips and to run open loop steppers with them. The board was pretty clean and very effective.
Rather than build a whole new board for Tommelise 3.0 I'm modifying that one and parking the third stepper controller and the eeprom memory buffer on a second board connected to the first by an I2C twisted pair. Here you can see the result.  The IR scanner board is on the right and the extender board connected to it by the I2C bus is on the left. You can see that there is considerable real estate in the middle of the board left free. I might be able to park the extruder controller there, but if not, I just create another extender board. I included the possibility of handling opto-endstops on the z-axis stepper controller. I need to add that in to the x and y-axis steppers on the old board. That is not a big thing to do.
The circuit diagrams shown in my previous blog entry, I2C-based Reprap control, are exactly what was used in the new board with one exception. The stepper controller circuit diagram that I posted had a small bug in it that I uncovered when I actually went to make the board. Here is the corrected circuit layout. 
The two pole connector that was on the right hand side of the board has been moved to the left (circled in red) above the 12 volt power feed and a mistaken pin assignment corrected. There is room there for endstops at both ends of an axis, though I've never used more than one and that for resetting the start point of the axis. The EEPROM buffer layout is a bit different in look from my earlier diagrams. This is a result of two factors. The first is that I'm using what is known as full-line Euro Card stripboard rather than milled, single sided printed circuit board. On a single sided pcb one tries very hard to minimize the number of jumpers. On stripboard, jumpers are the name of the game, which means that your board, though topologically identical looks very different. As well, I used twin, 18 pin sockets to house the EEPROMs rather than four, 8 pin sockets. I had the 18 pin sockets and didn't have any 8 pin sockets.
The next step will be to test out the card to make sure everything works and then to rewrite Tommelise 2.0's firmware for the new bus architecture. Using I2C should considerably simplify the firmware. As well, I will be able to do half and full stepping with the new cards instead of merely wave stepping. That has already shown me that I can get a LOT more power out of my z-axis linear stepper. Heretofore, the lack of thrust in the z-axis has been a continuing headache for me in terms of the reliability of positioning in the z-axis. It appears that that will be a thing of the past with the new controller cards if the tests are any indicator. Trackbacks
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Its a long time since I have seen (Vero board uk trade name of fibreglass strip board) I used this system in the 80's with some enameled wire called Vero wire this was very fine enameled wire the enamel vaperized when you heated with a soldering iorn. it had plastic combs that clicked into the Vero Bd to keep the wiring tidy it was Veros replacement for Wire wrap prototyping
See pic http://picasaweb.google.co.uk/lh/photo/4udgBTggGDslak1P7OUBOA?feat=directlink
I dont see any fly wheel diodes are they in the driver chips or on the steppers?
I looked up a data sheet It was slightly confusing the schematics of inputs and outputs on the Data sheet shows that internaly there are flywheel diodes.
The next item shows a typical aplication using a stepper motor in this they show externaly fitted Fly wheel diodes. possibly a belts and braces application note or the note was reused from a chip without internal fly wheel diodes .
Yes, the 754410 isn't exactly the best documented chip and it certainly doesn't come within miles of the sophistication you can get with the Allegro chips. It works well, though. It's cheap, simple, and it does what I need it to. :-)
may I suggest you take up the prototyping offer from the rrrf, and have them build you proper/commericial PCB's for these, that way more others are likely to take up the design! .
http://www.rrrf.org/prototyping-rd/
Naah, if somebody else wants to do that, fine. For my part, I'm reducing mine to stripboard setups and single sided PCB's milled by Tommelise. I think we need to get serious about self-replication and get away from all the "lets make it commercially" bs. Reprap should be about self-replication, not starting little companies, imo. :-)
I agree. I made the mistake of getting all the electronics from RRRF, and spend a tidy sum on shipping it to Australia. I have nothing against RRRF... they have some very good stuff available and the quality of the kits was great.
Knowing what I know now I would have made strip-board electronics and saved the money for the rest of the project.
I think the ability to generate a replicator design from a bunch of stuff at hand is the way to go. The software should be able to compensate for differences in the hardware so that the artifact designs can be shared but the hardware needed to generate them can be radically different. Ideally part of the software should be able to aid the construction of the replicator by being told what materials are to hand.
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