Powering a 5mw laser with board of education?
radicalgarbage
Posts: 4
Alright, so I have some very simple questions concerning the board of education...
If I have a laser that is rated for <5mw and it's working voltage is 3 volts, and the working current is <280mA, is it okay to run it directly off the vdd and vss pins on the board? Would the 5 volts and whatever current the regulator puts out be too much (enough to kill the laser diode)?
What sort of circuit would I need to build to get the voltage and current down if that's the case? I know a Zener diode probably fits in the circuit somehow from what I've gathered on Google but I'm kind of a n00b at this sort of stuff... Thanks in advance
If I have a laser that is rated for <5mw and it's working voltage is 3 volts, and the working current is <280mA, is it okay to run it directly off the vdd and vss pins on the board? Would the 5 volts and whatever current the regulator puts out be too much (enough to kill the laser diode)?
What sort of circuit would I need to build to get the voltage and current down if that's the case? I know a Zener diode probably fits in the circuit somehow from what I've gathered on Google but I'm kind of a n00b at this sort of stuff... Thanks in advance
Comments
which has an lm2940ct which is rated 1Amps .. but it also depends on how large the voltage is you put on the board .. as how bigger that voltage is .. the more power the regulator needs to dissipate and the size of the heatsink.
With a laser you only need to control current, not the voltage.
You can make a current source with a biggish NPN transistor which is rigged as an "emmiter follower".
You put the laser between 5V and the collector, and a resistor between emmiter 0V.
Now if you put a voltage on the base, the transistor will regulate itself that there is a voltage
on the emmiter that is 0.6 volts lower as on the base. So you can take one or more voltage
dividers to put between basic stamp and base .. so depending on which pins you make high
you get a certain current through the laser.
So the current through the laser is the voltage at the base minus 0.6 divided but
the resistance of the resistor at the emmitor. Also the voltage at the emmitor cant be to big
as you also need the 3v from collector to 5v say you would take 0.6v.
that also gives you an oppertunity to more a current limiter.
Say you would take another small transistor, put the emmitor at 0v and the base at the emmitor
of the first transistor than that transistor would start to work if the voltage at the emmitor reached 0.6v.
So if you put its collector at the base of the first transistor .. than if the voltage over the emmitor
resistor would get bigger as 0.6v then the voltage at the base would be limited.
So the current never gets bigger as 0.6v divided by the emittor resistor.
<a href="http://apsdev.com/stampscope/home.html">Basic stamp oscilloscope</a>
I'll post more on this and the project I'm working on once I get a little free time.
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·"If you build it, they will come."
Hooked it up with a battery holder for 2 AAA batteries as the power source and I think this is definitely safer for the diode. The laser doesn't seem as ridiculously bright as before and all is right with the world heh
In case anyone was curious, I'm using an old BS2, the BoE, 2 microswitches, 2 of those membrane style buttons (from an old PC gamepad), 2 LEDs, and a servo as a control system for a laser line that will sweep up and down in an automated fashion.
This is for 3d scanning with some software I found recently called "DAVID-Laserscanner".
It sounds like overkill, but the LEDs and buttons are there to make it easy to calibrate the servo's range of motion and get more precise angles for the laser line on the fly without having to reprogram the stamp every time I want to scan something of a different size or scale up/down the scene which I'm scanning
Post Edited (radicalgarbage) : 7/14/2010 10:17:37 PM GMT
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·"If you build it, they will come."
We had our twins' faces scanned on a huge fancy expen$ive system from http://www.di3d.com/index.php , quite nice. Full color, hi-res, amazing. But this poor man's approach looks just as intriguing!
radical: please post some sample scans when you can!
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·"If you build it, they will come."