This is an Atmel Mega8 based replacement for the GAL22V10 driver chips on the ODIN motion control board.
The hardware documentation and the firmware of this replacement module (referred to as "m8driver") is licensed under the GNU General Public License version 2 or (at your option) any later version.
The m8driver advantages over the standard GAL22V10 controllers
Electrical characteristics
Better electrical characteristics and much better noise immunity. Due to weak internal pullups and a Vin-low of max0.8V it is possible that noise from the stepper motors is picked up by the input signals of the GAL22V10. This will result in "ghost" steps that make a rattling sound.
The m8driver's ATMega8 is rated to a Vin-low of max1.0V (but in practice it's much higher) and strong pullups are applied to the inputs. So the m8driver is much less sensitive to noise.
Customization
The source code of the GAL22V10 firmware is not released by the original author of the device, so it is not easily possible to reprogram the device to other microstep sizes by the user. The closed source design of the original drivers does not allow the user to tweak the hardware to his needs. The ODIN author offers a reprogramming-service, but that is very inconvenient and does cost some money (shipping cost, at least) and time. The m8driver is released under the GPL, so you are free to modify it and tweak it to your specific setup. It's also easily possible to compile the firmware for other microstep sizes. The default is 25 microsteps, but you can override this by specifying STEPS=XX to the "make" command, where XX is the desired microstep count.
Lots of possible microstep rates
The m8driver can be configured from 1 microstep (fullstep) to 60 microsteps. Additionally you can get the 30 microsteps without modifying the hardware. (The original GAL22V10 drivers need electrical hardware modification for the 30 step variant.) Note that as the output DACs are only 4 bit, higher step rates than about 30 do not gain much (if any) precision. It is possible to get even higher than 60 microstep rates, if demanded by your setup, but this requires modification of the sourcecode. Please contact me, if you need this.
No electrical changes required
There are no electrical changes required to the ODIN board. The m8driver fits into the existing two GAL22V10 chip sockets. Only a small change to the heat sink is required to gain some extra space for the m8driver boards. But you can always remove the m8drivers again and re-install the GAL22V10. It's Plug-And-Play.
Download
Latest bleeding edge firmware and hardware schematics can be downloaded using the Git version control software by issuing the following command:
git clone git://git.bues.ch/cnc.git
To browse the Git repository online, go to the gitweb interface.
The m8driver stuff is in the subdirectory "odin_extensions/m8driver" of the GIT tree.