P3 Flexmod

[The_Doctor]

Slow start is good, and the slow start circuit should drop out once the diode is running.

I'll also tell you that on a proper slow start system, it should not take longer then 30 milliseconds for the slow start to function. You should not see the slow ramp up in the diode light by eye.

Steve

Exactly my point. Any longer than the maximum slew rate is only needed to make sure that any starting transitions don't peak high before things settle. My own driver rises on an exponential slope at startup, and settles within about 10 microseconds, and the slope to full current rises to settle about 20 microseconds later. This is faster than 30ms by a thousandfold, but it is good enough. I can repeatedly jam splayed wire ends on a 12V battery drawing rough sparks if I want, the transitions never hit the laser diode. So I agree, any longer than 30ms is luxury.

Swami, I think the ambient light ought to be enough to solve the first point, if it doesn't the projector is likely too bright for the conditions. Though I accept that we can't easily scale this and not at all fluently, a diode is what it is... We can scale other lights though, set a mimimum so we don't perceive the annoyance in context.

The timing thing is more interesting, I'll accept this if there is no way to avoid it. Thing is, DPSS does have nastiness, direct diodes not so much, I thought. What you're saying seems to imply that they have much slower responses than I thought. Hundreds of microseconds, where I thought they'd be a thousand times faster. I've not seen this because I have never modulated more than one colour. If the degree below threshold can influence the timing of fast modulation accuracy for colour mixing at low levels, then it's worth using to do just that. But again, can this not be done purely by setting that sub-threshold value and accepting that if very low, there may be slight impact on diode life? I still think it's worth accepting the slight low level light because in proportion to full it will be very weak, and as with audio the best way to hide low level aberrations is in a 'noise floor' that our brains will tune out.

[swamidog]

doc,

it's quite noticeable on my little DI RGB build projector. it's only about 300mW, so a reasonable brightness for my living room.

Exactly my point. Any longer than the maximum slew rate is only needed to make sure that any starting transitions don't peak high before things settle. My own driver rises on an exponential slope at startup, and settles within about 10 microseconds, and the slope to full current rises to settle about 20 microseconds later. This is faster than 30ms by a thousandfold, but it is good enough. I can repeatedly jam splayed wire ends on a 12V battery drawing rough sparks if I want, the transitions never hit the laser diode. So I agree, any longer than 30ms is luxury.

Swami, I think the ambient light ought to be enough to solve the first point, if it doesn't the projector is likely too bright for the conditions. Though I accept that we can't easily scale this and not at all fluently, a diode is what it is... We can scale other lights though, set a mimimum so we don't perceive the annoyance in context.

The timing thing is more interesting, I'll accept this if there is no way to avoid it. Thing is, DPSS does have nastiness, direct diodes not so much, I thought. What you're saying seems to imply that they have much slower responses than I thought. Hundreds of microseconds, where I thought they'd be a thousand times faster. I've not seen this because I have never modulated more than one colour. If the degree below threshold can influence the timing of fast modulation accuracy for colour mixing at low levels, then it's worth using to do just that. But again, can this not be done purely by setting that sub-threshold value and accepting that if very low, there may be slight impact on diode life? I still think it's worth accepting the slight low level light because in proportion to full it will be very weak, and as with audio the best way to hide low level aberrations is in a 'noise floor' that our brains will tune out.

[The_Doctor]

Agreed. But are you trying for total darkness? If you turn off all other significant light sources you'll notice pretty much anything. My method would be to use a dimmer and set to a low level that let me easily ignore the lowest level laser light. I doubt many clubs will ever be in total darkness... People are too accident prone for most clubs to dare risk it.

[swamidog]

not total darkness. the light is dim, but comfortable for dorking on my laptop and watching tv.

Agreed. But are you trying for total darkness? If you turn off all other significant light sources you'll notice pretty much anything. My method would be to use a dimmer and set to a low level that let me easily ignore the lowest level laser light. I doubt many clubs will ever be in total darkness... People are too accident prone for most clubs to dare risk it.

[The_Doctor]

Well you could always use a lumia to make your noise floor.

[swamidog]

Well you could always use a lumia to make your noise floor.

got that covered..

[shrad]

a solution would be to command the beam suppression via a digital line, or even the intensity channel, wouldn't it?

[The_Doctor]

got that covered..

Thought you might. Is why I mentioned it the way I did..

Shrad, you could even do it directly on each colour line. If I were coding for this I'd set the driver electronics to extinguish the diode, regardless of impact on diode life, then solve that by scaling all but the 0 value to fit the range I wanted, from full brightness to lowest, being below threshold but as close to it as I could get away with. That way 4095 of the 4096 values in the 12-bit dynamic range get used to match colour on all scales, and timing is made acceptable at low levels where needed, then all I need to do is avoid sending a zero EXCEPT when I want total blanking. This avoids complexity in both the digital signalling.and the analog electronics other than the need to recognise the threshold between signal for 0 and 1 to cause full blank at 0, and as the difference is 2.4mV for 12 bits on a 10V scale, this is doable especially where the DAC is close to the laser driver to limit analog noise. Maybe use one pot on the driver to set deep threshold for full blanking instead of one for the original lasing threshold, as that would be hardwired now that software is used to scale the actual placement of value 1 for sub-threshold. The operator or show designer gets total control, they just have to know that zero MEANS zero, and that 1 is the lowest value for normal range.

I think this might work while avoiding any threshold pot at all, just use a fixed divider and FET to switch off all current for zero. Small, no moving parts, a driver could be smaller and cheaper this way.

[buffo]

1) diodes still glow even below threshold. the glow is bright enough to be projected beyond the galvos and it's quite distracting in graphic and abstract shows.

This is why you have a mechanical shutter (GM-20 or equivalent) in your projector.

That way you can keep all your diodes simmering at just below threshold (for optimal blanking response), and use the shutter to block the dim, non-coherent emissions from the diodes when you aren't actually projecting something.

Adam

[swamidog]

that doesn't work while shows are playing ;(

This is why you have a mechanical shutter (GM-20 or equivalent) in your projector.

That way you can keep all your diodes simmering at just below threshold (for optimal blanking response), and use the shutter to block the dim, non-coherent emissions from the diodes when you aren't actually projecting something.

Adam