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Laser Scanning Display Project

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 ;D (I hope you had some fun!)
It is a coded string, that is converted into the image array during setup.
It could be passed by serial. maybe we add a second interrupt. When a message is coming we stop the laser and do first the conversion of the string and continue afterwards with the laser.

There is a next challenge for the software, to find a smart way to pass the message. Twitter? Email? website (pass the input thru php to the arduino over a free port of the router)? 
Any ideas?

I ordered a green laserdiode (we will see). I make also a new design for the mirrorholder. I want to use true glasmirrors - this is better than my polished mirrors.  And the angle mirrors can be finetuned in the new holder.


Dear ElectroNick,
I have a problem with my circuit. My new laser needs 2.2V and aprx 400 mA - too much for the Arduino. Therefore I added a transistor 2N2219.
If I exchange the Laser with a LED (or my small Laser), the LED is on. If I add the new laser, the LED goes off, ampere is a little bit higher (aprx 40mA) and nothing happens with the new laser.
The new laser itself is also working, if I connect directly to GND.
What is my mistake? Thanks for help...

Are you talking about just the laser diode itself or a laser diode module (as in a laser pointer) - the latter being the diode and the driver in one package?

There are a couple of issues with this circuit.  The supply voltage is probably 5V coming from Arduino, right? You have 2.2V up on top, not sure what would supply that. Also, if you need 2.2V exactly, make sure you account for approx 0.7 V drop in the silicon-based transistor.  So, to have 2.2V across the laser, you would need at least 3.5V from your supply. Since your more convenient supply is probably going to be Arduino's 5V (I might still use it for 400mA in a pinch although the 7805 regulator on Arduino may get very hot, just don't run it for a long time) - you will need a 3.75Ω - 4Ω (I think there's a 3.9Ω standard size) current limiting resistor.

Note that if you have a laser diode module, you don't need a current limiting resistor because the driver regulates the current by itself. But then the voltage will have to be higher due to losses in the driver.

400mA is a SERIOUS POWER laser diode! Be extra very careful with it! I would find out the least amount of current it starts lasing on and only use this much for testing / troubleshooting the circuit. Only when I need to project the image onto a building or something that that requires this much power, I would crank it up to full.

And last but not least, I've never used such powerful laser diodes without drivers, so I'm not sure how it's going to work. If it does work, you probably will get just a couple of hours of useful life out of it if it's run at the max current. So, just in the name of saving an expensive diode, I would drop the current requirement to 100-150mA   (15Ω current limiting resistor @ 5V)

I am curious, how much is a 400mA green laser diode these days? Green is the color I'm missing in my collection, perhaps it's time I should go buy it   :)

It is a laser module. I thought to use a separate powersupply for the Laser and to realize the separation from Arduino's 5V with the transistor circuit - so use the arduino only to control the base of the transisitor.
Do you see a mistake in the circuit?

The circuit is working - I was irritated, because the green laser itself is too slow. I removed the module (by luck it was just a connector) and controlled directly the diode. Just to find out, that the green laser needs some time to start lighting. I estimate that the maximal frequency is aprx 10Hz.
I ordered also a stronger red laser. So I wait for that one!!


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