The laser's back and this time I'm finally getting around to trying out some real-time effects using JACK. This is a simple circular oscilloscope (look ma, no retrace!) spinning at some multiple of Middle C frequency, which works particularly well for music. I found that chiptunes, due to the simplicity of the waveform, show up in very interesting ways. Keep in mind that this is a crappy 30fps digicam capture; it looks a lot better in real life. The sync is also a wee bit off here, in real life it's perfectly synced by design (audio and laser outputs are synchronous).

The song is Visitors From Dreams by Dma-Sc :)

Although not shown, blanking and brightness modulation also works, though the laser has trouble achieving full power unless it's on 100% of the time. Here (fully on), it's probably putting out 40-50mW or so - I measured 60mW when I got it but I run it a bit lower here for safety.

Note that the room lights were on and the window was fully open when I took this video: I had to turn down the exposure on the camera to reduce the artifacts caused when the image is acquired from the camera sensor. You can still see them somewhat, particularly right at the very beginning, above and below the circle.

Random tidbit: the blink at the beginning was caused by a JACK xrun that occurred as the music started. The safety controller on board the laser kicks in and shuts down the laser at most 0.5ms after it senses a failure of the software, and keeps it that way until it gets a stable signal for a few hundred ms. I do this by dedicating one soundcard channel to a 1Khz pilot signal - when it disappears, even for one cycle, the safety controller powers down the laser. It also does power supply monitoring and short circuits the laser as soon as it senses the main PSU output falling, which hopefully should eliminate any dangerous (for the laser) transients. (less info)