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The controller board that the laser cutter came with is designed to connect to a PC with a parallel port. I planned from the outset to replace this. The board I chose to use instead is the EiBot Board, a derivative of the UBW (USB Bit Whacker) board. This board was designed by Brian Schmalz for the Egg-Bot, a little robot for plotting on eggs, lightbulbs, and other small round objects. It's available from Evil Mad Science and SparkFun.

My interest in it was as a stepper motor driver I could control via USB from any modern computer (it appears as a serial device, and it is controlled by sending it simple ASCII commands).

The trick is to connect the EiBot board to the laser cutter.

old and new controllers

The EiBot board is the little white board. The existing controller uses three connectors (purple boxes) to talk to the rest of the laser cutter. The leftmost connector gets +5VDC (for the logic) and +24VDC (stepper motor power) from the power supply, and sends a "laser on" signal to the laser power supply. The middle connector connects to the small green board above the controller, which in turn houses the X limit sensor, and connects to the Y stepper motor and the Y limit sensor. The righthand connector connects to the X stepper motor. I don't have these connectors onhand, and replacing the nice flat flex cable would be a pain, so I elected to use the controller board as a passthrough. I can easily get access to the stepper motor power supply voltage and stepper motor outputs at the TEA3718 stepper motor chips (yellow boxes). A little circuit tracing revealed I can get to the limit sensor inputs and laser control at the 40106 hex inverting Schmitt trigger chip (blue box). I decided the least invasive way to do this would be to remove the relevant chips, insert header pins, and solder wires to the appropriate pins.

headers with wires

I attached a barrel jack to the stepper motor power leads, and hooked everything to the EiBot board.

controller wired to EiBot board

Then I installed the whole schmutz into the laser cutter, cabled everything up, and applied power.

Controller installed, power LEDs lit

The power LEDs lit happily, and the EiBot board responded to commands via USB. Time to see if I can use it to control the laser cutter's stepper motors.

Success! The motors work nicely, and move the laser gantry around like they should. I don't currently have the EiBot board controlling the laser, but I figured it was worth powering up the laser manually and trying a simple cut. I grabbed a scrap piece of cardboard as a sacrificial object to try cutting.

Yow! It cuts! Focus is a little off, copious smoke is produced (stinky!), but it does the job! Makes a nice fine line with good control. Next steps are to hook up the smoke fan and duct and vent it outside, add laser control, and use the free extensions to let me control it with InkScape.

January 2014

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