[Cyborg] 200 laser diodes

Eric Boyd mrericboyd at yahoo.com
Thu Jun 3 00:06:51 PDT 2010


Thanks Christoph.

Sadly, there are two egregious errors in *my* calculations:

1) The laser are only 5mW, not 50mW

2) There is a big difference between the optical power of the laser and 
the electrical power it consumes, i.e. the diodes are not 100% efficient.

I found a different part that actually gives a current rating:

http://www.futurlec.com/Laser_Diode.shtml

It's a 10mW laser (twice as powerful), operates 2.3V @ 45mA (note this 
does implies only ~10% efficiency!).  But, if we assume our device is 
similar but half power, we come back to 23mA, which is still totally 
driveable using Arduino pins, although you might want to limit yourself 
to 9, as per Christoph's research below.

So long and short my two egregious mistakes kind of canceled each other 
out, and everything still works :-)

Eric




On 6/2/10 11:44 PM, Christoph Maier wrote:
> On Wed, 2010-06-02 at 23:06 -0700, Eric Boyd wrote:
>> Indeed!  My plan is to basically hack a North Paw board into doing the
>> work, but according to my calculations you should just be able to use an
>> Arduino.  50mW laser diodes.  If we assume they have a 3V drop (the page
>> says "battery: 3-5V"), that means 16.7mA each, which you can drive with
>> an arduino pin.  Anyone know the total power an Arduino can drive/sink?
>>    I'm just wondering how many of the pins you could have going at once...
>>
>> Eric
>
> According to
> http://www.atmel.com/dyn/products/product_card_v2.asp?part_id=4198
> http://www.atmel.com/dyn/resources/prod_documents/doc8271.pdf
> chapter 22, Absolute Maximum Ratings,
> you can draw up to 200 mA through the power pins
> and 40 mA through any one I/O pin,
> meaning that without a driver, you shouldn't try to drive more than 10
> laser diodes directly.
> (Note that an earlier version of the data sheet quoted 300 mA absolute
> maximum rating; this means that you can probably get away with driving
> more current for a prototype, but NOT repeat NOT for stuff you want to
> sell commercially.)
>
> Christoph
>
>
>


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