Now that I have the
running the steppers, I'd like to have it turn the laser on and off too. Normally, the
was designed for has a servo to raise and lower the pen. This is controlled with a pulse width modulation (PWM) output. But I needed
an on/off signal to feed to the laser. Looking at the documentation,
I noticed references to a solenoid output, which sounded like just what I needed.
Looking at the earlier versions,
I could see the circuitry to drive the solenoid,
but that circuitry isn't present on the board I have.
Looking at the schematics, the I/O pin that drives it is now used for another purpose.
I downloaded the firmware source code and tried to dope out what the current code did,
but I wasn't able to figure it out.
So I sent a note to the designer and asked him about it.
He sent back a prompt and helpful reply, stating that the RB4 output should have the solenoid signal.
I soldered a header on the appropriate pins and hooked up an LED (and current limiting resistor). At first, I had the LED hooked from +5V to RB4,
but that voltage isn't supplied by the board when it's running from just USB, so no joy. So I hooked the
LED between RB4 and ground, and sure enough, it followed the pen up/pen down state.
So I grabbed a handy male-female jumper wire and plugged the female end
onto the RB4 post (lower left), and ran the male end into the TTL "L" input on the laser power supply (upper right).
I fired up InkScape with the Egg-Bot extensions, and exercised the pen up/pen down command.
Sure enough, it controlled the laser, but with inverted sense. Happily, the laser power supply also has a TTL "H" input,
so I ran the lead to it instead. This is convenient, as the manual button can use the "L" input and the EiBot board can
control the "H" input, and I don't have to wire-or anything.
Testing showed that the EiBot board now turned the laser on for "pen down" and off for "pen up", just what I wanted.
I played with the Egg-Bot extensions (they're very configurable) some to match the laser cutter better,
used the "polygon/star" function in InkScape to draw a simple star,
placed a scrap of acrylic in it (thanks for the suggestion, graysoul), pressed the "laser enable" button,
and told it to plot.