Active forum member Woodpecker went looking for alternatives to the Adafruit motorshield, and came across this dual-stepper shield made by ITead Studios, and sold by Komputer.de in Germany. I got a couple, and they are very reasonably priced. These are pre-assembled, based on the A3967 driver chip – the same ones that Brian Schmalz uses in the EasyDriver boards. They can drive upto 750mA per motor, which is a bit more than the L293Ds in the Adafruit design (though that can be upgraded with SN754410 drivers for those that are as infatuated with adafruit as I am).
The main feature of this shield is that the A3967s are serial steppers, which means they use fewer pins, and the shield happens to use pins 2 through 9 on the arduino. Which means that the magic pins 10, 11, 12 and 13 are free – and these are the pins that the SPI interface appears on in the Uno-sized boards. That opens up the possibilities of using a pre-assembled SD card reader with the Uno, which is interesting. Now I’d more-or-less given up on running an SD card with an Uno, because of the double-whammy of needing to rewire and because of the memory limitations.
HOWEVER, if this board removes one of those impediments, then the game is perhaps afoot again. I can conceive of a firmware that is very minimal – just responds to vector graphic commands only, and is optimised for standalone drawing. Is this worth having? I suppose I can’t know until I try it eh.
The other feature of the shield, is that all the spare analog pins are broken out to three-pin headers, and the motor connections themselves are exposed as four-pin headers AND screw terminals. So this could be used without the faintly comical terminal adapters that I’ve been making up so far.
The downside: There doesn’t seem to be a way to turn these off. The EasyDriver breaks all pins out so motors can be enabled / sleeped, but this shield appears not to. This is a bit of a blow, because it means the drivers and motors are energised as soon as the board has power applied, and it can’t be turned off programmatically.
The A3967 chip is also less tolerant of bad behaviour like unplugging the motors while it’s on – this is much more likely to damage the ICs than with the L293Ds, so be careful.
Oh and one other thing – these are HOT! Makes the whole arduino hot. I believe the IC will always be hot, and probably well within threshold, but I think heatsinks will be the order of the day again.
Anyway, I have released a new firmware that is built for the ITead shield. It is otherwise identical to the regular firmware, but dispenses with the AFMotor library. The servo pen lift is now also controlled from pin A0 (aka d14), which is the first three-pin header in the block on the motorshield. You can see that on the picture.