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### Topic: Laser Harp Help? (Read 4821 times)previous topic - next topic

#### bibre

#15
##### Aug 06, 2012, 09:24 amLast Edit: Aug 06, 2012, 09:26 am by bibre Reason: 1

All lasers will be on (it's the Harp), and their corresponding photo sensors will be active so that as you block the laser beams with your fingers they will play their note. Am I correct?

WOW!, this is very nice and creative. Congrats!

And when it works, you'll have to do a piano !!!     XD
Billy     http://www.z-world.com/operations/gbremer/

When you've eliminated the impossible,
whatever remains, however improbable, must be

#### jnighlight

#16
##### Oct 13, 2012, 12:03 am
Alright guys, sorry for the long wait time. I'm back and ready to work on my harp again. As it turns out, Calc 2 in college takes up a lot more time than you would think.
Anyways, I've been looking at the lasers themselves and they seem to have a resistor in front of the line that leads to the laser, meaning that it needs less power. But they *all* have the resistor (all 8 of my lasers). So here are my questions: How to I tell what kind of resistors they are? I have a multimeter - can I use that? Also: how do I calculate the energy the lasers will need? Is it something like...

Voltage needed by the individual lasers (so, if they each need 4.5 volts, I need one 4.5 volt wire)
with
the amps each laser needs * the number of lasers (8 lasers, 15 mA each, so 120 mA)
and
one resistor equal to the voltage of the resistor already in the lasers BUT equipped to handle 120mA

Is this correct, or am I missing something? Thanks for your patience and help all!

#### jnighlight

#17
##### Oct 13, 2012, 12:05 am
And you are correct bibre! That's what I'm shooting for.
And thanks! I just found photoresistors and knew that I could make *something* cool. And I wanted it to involve lasers. So I came up with this!

#### Grumpy_Mike

#18
##### Oct 13, 2012, 12:40 am
Quote
one resistor equal to the voltage of the resistor already in the lasers BUT equipped to handle 120mA

No you don't.

Resistors are measured in ohms not volts. Each laser diode needs its own resistor, you can not combine them
Yes use a multi Meyer set on resistance to measure resistance. Do this only when the power is off.

#### bibre

#19
##### Oct 13, 2012, 02:26 am

Good luck!
Billy     http://www.z-world.com/operations/gbremer/

When you've eliminated the impossible,
whatever remains, however improbable, must be

#### jnighlight

#20
##### Oct 13, 2012, 04:03 am
Ok, cool. So I need 4.5 volts at 120 mA with 8 *insert number after I test here* ohm resistors?

Also, why can't I use just one resistor? Wouldn't the voltage or amperage difference be the same after a larger resistor as 8 smaller ones?

#### Grumpy_Mike

#21
##### Oct 13, 2012, 09:52 am
No it would only be the same if your load was a linear one, like another resistor.  Your laser diode is like an LED, it is non linear, that is it does not obey Ohm's law. The resistor is to approximate a constant current device. If you put all the laser LEDs in parallel they would not shair, one would take more current and blow, then the next one and the next until they were all blown.

#### jnighlight

#22
##### Oct 16, 2012, 12:16 am
Ok, so I checked the resistance and it came out as 0.00, so I'm beginning to doubt my "resistor theory". Does anyone know what the piece on top is? Right below the metal rectangle? Thank you!

#### jnighlight

#23
##### Oct 16, 2012, 12:24 am
Ok, I lied. I set the multimeter to 200 instead of 20M and got a pretty steady 130. Does that mean I need a 130 resistor? (With the bands equaling to 13 * 10 to the power of 1?)

#### jnighlight

#24
##### Oct 16, 2012, 02:13 am
So...brown orange brown for the resistor?

#### Magician

#25
##### Oct 16, 2012, 03:58 am
Right, resistor 13 x 10^1 =130
I used 91 OHm for red lasers, get 22 mA, little bit high for arduino, about 100 should be just fine

#### jnighlight

#26
##### Oct 17, 2012, 11:38 pm
So...if those resistors are already in place...Don't I just need 8 33ohm resistors for each of the lasers?

#### Grumpy_Mike

#27
##### Oct 17, 2012, 11:50 pm

So...if those resistors are already in place...Don't I just need 8 33ohm resistors for each of the lasers?

Thought you said they were 130R?

#### jnighlight

#28
##### Oct 18, 2012, 12:05 am
I believe so. When I used my multimeter on 200 for resistance, it showed a steady 130. Does that mean 130R? Or does it mean 130 ohms? or both?

#### jnighlight

#29
##### Oct 18, 2012, 02:35 am
Oh, I see the confusion. The resistors in the lasers are 130. However, since they're built in, I just need to make sure that 4.5 volts with 15 mA gets to them! So, I can use the built in resistors and just use 8 33ohm resistors to limit the 5 volts from the arduino to each laser (along with each laser's built in resistor) so that each laser/resistor combo is getting 4.5 volts at 15 mA, which is what they'd be getting from the 3 batteries.
The "replacing the resistors already in the lasers" was adding an extra step I didn't need. I think I'm gonna get some friends together and finish this project this weekend. Any suggestions, criticisms, thoughts?
Thank you all for your help! If we get it done, I'll be sure to post pictures!

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