Bug #24

Laser PWM doesn't seem to be working at all

Added by david almost 10 years ago. Updated almost 10 years ago.

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We've added a connector between the laser current wires and hooked it up to the correct connector on the board (exhaust enable). The laser doesn't turn on anymore regardless of the 'power' level specified in Visicut.

In fact, checking with a battery, an LED and resistor hooked up to the pins of exhaust enable shows that the exhaust enable isn't doing anything at all. We've swapped over the optocouplers but that didn't help either.

For now, we've added a jumper to the laser pwm connector and are using the front panel 10-turn pot for laser power. It would be great, however, if PWM worked.


#1 Updated by david almost 10 years ago

I just ran some tests with a multimeter hooked up to the unisolated exhaust enable output and it seems to modulate. Is it correct that the power signal is inverted (i.e. a higher power value results in a lower duty cycle)? At least the pin on the mbed is working and the firmware is capable of changing the duty cycle.

Next up is checking whether the signal reaches the other end of the optocoupler.

#2 Updated by david almost 10 years ago

Okay, that was an easy fix! Because we initially did not plan on using the exhaust enable functionality the resistors were not soldered on the board.

Now that they are in place the laser does seem to support PWM.

However the laser stays on during start up. I hope I haven't destroyed anything in the process. Any tips on how to troubleshoot this? Of course this can be solved by having the laser switch in the off position when it's not in use, but still this is a dangerous mistake in the hardware/firmware.

#3 Updated by peter almost 10 years ago

Please mount all 4 resistors for the opto-couplers by default. We might use the other outputs in the future!.

Also: the "laser on at startup" bug is solved in the latest (development) firmware version. See firmware page for link.

#4 Updated by peter almost 10 years ago

  • Status changed from New to Rejected

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