SOLVED Laser diode has 3 wires = confusion

[JimboZA]

Can anyone tell my why this laser diode has three wires?

To power up the laser I'm guessing I need to put some VDC across pins 1 and 2? But what's the other diode on pins 2 and 3 for?

http://www.mantech.co.za/Datasheets/Products/ADL-65055TL.pdf

I guess the datasheet does actually explain this somewhere but it's a tad arcane for me and I'd appreciate it if someone can tell me how to wire this sucker?

Also, that operating voltage of 2.2 to 2.5 seems a bit awkward.... wondering if it would be ok to drive it at 3.3 from the Uno which can supply the necessary current.


(This one has two wires which makes more sense to me. But apart from being 3 times as long and twice as wide, it's also twice the price: http://www.mantech.co.za/Datasheets/Products/VLM65001-V43.pdf )

[retrolefty]

Can anyone tell my why this laser diode has three wires?

To power up the laser I'm guessing I need to put some VDC across pins 1 and 2? But what's the other diode on pins 2 and 3 for?

http://www.mantech.co.za/Datasheets/Products/ADL-65055TL.pdf

I guess the datasheet does actually explain this somewhere but it's a tad arcane for me and I'd appreciate it if someone can tell me how to wire this sucker?

Also, that operating voltage of 2.2 to 2.5 seems a bit awkward.... wondering if it would be ok to drive it at 3.3 from the Uno which can supply the necessary current.


(This one has two wires which makes more sense to me. But apart from being 3 times as long and twice as wide, it's also twice the price: http://www.mantech.co.za/Datasheets/Products/VLM65001-V43.pdf )

Ok, the first device is a 'raw' laser diode. It has both a laser diode and a photodiode mounted internally. This kind of 'raw' device requires special driver circuit to control the laser diode current so as not to destroy it. The photodiode is there to give a feedback signal to the driver circuit to help maintain laser current to desired amount. You DO NOT power this laser by just applying a DC voltage to it, it will self distruct. You need to control the DC current to the laser diode to it's safe operating range. You could probably power this led with just using +5vdc and a proper sized series connected resistor to limit the current draw of the laser diode to at or less then it's safe maximum current, say around 110 ohms and just not use the photodiode lead.

The second device is a laser module. This has both a laser diode and a built in laser driver module. This kind of device is powered with just applying the proper  DC voltage to it.

See the difference?

Lefty

[JimboZA]

Which explains why the second one is bigger and more the point, more costly.

Thanks Lefty.

Edit.... I see, alas, that it's over the current limit for an Uno I/O pin so I guess I'd need to switch it with a small transistor like a BC548.

[retrolefty]

Which explains why the second one is bigger and more the point, more costly.

Thanks Lefty.

Edit.... I see, alas, that it's over the current limit for an Uno I/O pin so I guess I'd need to switch it with a small transistor like a BC548.

Well I read the datasheet as saying typical forward operating current is 25ma, that would work fine directly with an output pin if you size the resistor in series to 110 ohms as I said.

Lefty

[JimboZA]

Bought one of the pointer thingies this morning.

Now my daughter and I will mount it on the pan / tilt bracket and do a Star Wars thing with two servos.

Just think.... we can now tease the cat without even being in the house. Always knew this science stuff would come in handy....