XY table from DVD drives - how to make a grbl-compatible stepper driver?

Hi,

I have disassembled two DVD drives. The goal is to build a mini laser engraver, but I'd like to start with an XY table and deal with the laser diode later.
My aim is to have the kit open for upgrades, so I'm not going to reinvent the wheel and want to use well-established standards of interfaces.
The firmware I'd like to use is grbl, as it gives all I need (G-code, steppers, limit switches) and is written in C that I'm most familiar with.

First things first, I'd like to make a driver for these two steppers which moved DVD head. They are well-documented bipolars which get up to 500mA per coil. As I have some L293D and Atmel chips laying around, I prefer these components.

As I understand, the main controller communicates with motor drivers with 3 wires: DIR, STEP and ENABLE. A pulse on STEP should make the driver read DIR and move the motor one step in required direction. ENABLE tells whether I should energize the coils. That looks simple, but perhaps I'm missing something?

You will find it much easier to use standard A4988-based stepper driver modules than the L293D, and they will work much better (i.e. faster because of the constant current drive, suitable with a wide range of supply voltages, and they will generate less heat) . As well as the Pololu originals, clones are readily available on eBay. They already have STEP and DIR inputs, and unlike the L293D, they support microstepping. Be sure to turn down the current to 500mA or less using the pot.

Edited 1 time(s). Last edit at 12/23/2014 10:24AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I see some StepSticks locally available for approx. $5. Did you mean these?

Anyway, I'd like to try building my own driver with the parts I got right on my desk: L293D and ATtiny85. There are some free evenings coming during Christmas and I can spend them over the breadboard and learn something before any new components arrive. If I understand the protocol well, in the microcontroller I should:

1. code the truth table for the motor,
2. provide an interrupt handler activated by raising slope on the STEP input,
3. in the handler check DIR level and cycle over the truth table accordingly, then energize coils accordingly via the L293D.

And it seems that halfstepping is possible on L293D (or perhaps even microstepping if I harness PWM into the process), so there's a lot to learn