Old 04-08-2015, 07:43 PM #1
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Talking A design for solid state precision touch control

Hi guys!

One of the aspects of our custom laser builds that I always thought could be improved is the fixed output mode circuitry that we have.

I have been finding out about (not-so) recent developments in flashlight hosts which have rotary magnetic mode switches. This is a ring mounted on the host which you can rotate to switch through a larger (8 or so) number of mode settings, which is a much, much more user friendly interface than manually pulsing a clicky tailswitch. I believe the mode of function might be a hall effect sensor (and the rotating ring has a magnet or multiple magnets on it).

While that is nice from a tactile point of view, it is not nice from other industrial aspects because it requires manufacturing a bunch of stuff and lubricating the thing, and so on. It will begin to fail when sand or mud is brought into the picture. I have read about reports of grease coming out of these rings. That's bad!

So instead I would like to see how practical it is to bring laser (and we might as well support plain-jane LEDs too!) drivers into the 21st century by using a multi capacitive touch electrode sensor (such as the MPR121) and a microcontroller.

An MPR121 has 12 electrodes which can be measured in a semi analog way, but the sensor is interfaced digitally.

So as long as we can somehow build a number of electrically separate pads onto the surface of a host (this shouldn't be *too* hard), we can have a laser that we can power on and just slide a finger along the side to scrub the power up and down in a really smooth way. It will even be possible to flick with "momentum" like smartphone scrolling.

However the other component of this is a laser driver circuit that can take a digital power input value. I don't actually know much about the designs of the popular drivers in use these days. Hopefully someone in the know there can comment on how possible such a design is. I think it should not be hard considering they already use tiny pots that we adjust with a tiny screwdriver, so in theory a DAC can get it done without any changes to an existing driver, (but we want to avoid using a DAC if we can, and also we want to probably use PWM *however* I also see benefits in having the freedom to scrub actual CW amperage).

Thinking about it a little more, I do believe these laser drivers we use are all analog circuitry, so a DAC may be unavoidable without doing complete re-designs.

Oh... hmmm... let me think... 10-bit 32kHz PWM from a cheap arduino-compatible microcontroller driving an RC low-pass filter for a poor man's DAC might be just the ticket. May require a rather large capacitor, but mostly it will be completely acceptable to have a very slow and smooth filter so as to feed the driver with a smooth waveform -- we won't mind having the output smoothly ramping to reach the setting.

At any rate, this is just going to be another (tiny) PCB that shouldn't end up costing any more than $30, though the control surface component is the more difficult aspect of it now I think.


__________________
When setting up LFI make sure you check the "Laser On" Option to turn on the signal!! This took me forever to figure out.
M-140 445nm@ 1800mA in L2X body (I have both a 2x18650 and 1x18650 L2X tubes that I drive with either 2x18650 or 2xIMR18350) with G2 LFL lens
Mitsubishi "500mW" 638nm @ 1400mA in Solarforce P1D Grey, beautiful custom Copper heatsink in a waterproof configuration and with a G2 lens You have outdone yourself Flaminpyro!
M-140 445nm @ 1800mA Lazeerer X-Drive 2x14430 host thanks Ehgemus
Crooked 500mW O-Like Crown 532nm thanks Susie (but damnit, it's mounted crooked)
Mitsubishi "300mW" 638nm @ 775mA in Solarforce L2T Waterproof
A-140 445nm @ 1500mA flexdrive, Aixiz 445 lens in Solarforce L2P Waterproof thanks Jayrob
BDR-S06J @475mA L2P thanks Flaminpyro
LPC-826 in Aurora SH-032 Stainless @417mA
PHR-803T @ 85mA

Last edited by arcaneinsomniac; 04-08-2015 at 08:10 PM.
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