vendredi 25 octobre 2013

My stencil CNC cutter

My stencil CNC cutter
Part one : Laser driver

Regulate current: 

The current supplied by the battery is rather stable, but in most cases, is too much to drive a laser diode. For instance, a DVD-burner laser diode would need about 200-250mA of power at about 2.5-3 volts(for any long life span to actually be expected of the diode). Laser diodes are, unfortunately, a very light load when wired directly to a battery, and an alkaline battery would easily put out about 500mA or more, and lithiums put out 2 or 3 times that much! This too is an instant death situation for our beloved laser diode. Although very simplistic, it is not that common to find a flashlight with the right current regulation, and most of us would like to be able to control the current supply by using a potentiometer.

Current regulation is the tricky part of this circuit. The chip that I like most for current regulation is the LM317. The chip can be used as a voltage regulator and as a current regulator. This guide will use a capacitor as a voltage regulator since the battery's voltage is, for the most part, already regulated and stable, while all we need to do is limit the current that we let flow into the diode.

Laser diod:
What you will find in different drives:
- In a DVD-RW there are 2 burning diodes: Red for DVD and infraref for CD.
- Weak red lasers 1mW from DVD-ROM (read-only drives) are suitable only for a small laser pointer or poor laser show, they won't burn anything.
- V combos CD-RW/DVD-ROM (burning CD and read a hangover), there's a burning infrared dide and weak red diode (as in DVD-ROM)
- And finally, the lasers from CD-ROM are absolutely useless. I mention this list so I avoid stupid questions whether the diode from a CD-ROM will burn.
Warning! Laser diodes from DVD-RW drive are emitting visible and invisible laser radiation and they are extremely dangerous! Their light can permanently damage the eyes. You must never look into the working diode even without the lens or point it on a reflective surface. Laser beam can cause burns or fire. This is usually a Class IIIb laser. Everything you do at your own risk.

Schematic of current power supply for double laser from DVD-RW burner drive with switch for selecting operation mode (RED - INFRARED - BOTH). The resistor determines the output current to the laser diodes using the formula I = 1.25 / R. LM317 needs a heatsink. The voltage drop of infrared laser diode is 2.15 V and the voltage drop of red one is 2.5 V. 

                                                                 250mW open can laser diode be continued

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