Laser Scanning Display Project

[Georg]

  (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.

Bye

[Georg]

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...
Bye

[ElectroNick]

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   

[Georg]

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?
 

[Georg]

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!!

[ElectroNick]

Yeah, 10Hz isn't going to work for sure  I have a nice driver that does approx 10kHz (or in other words, 100µs pulses) - and even that was too slow, so I had to ditch the driver.

I would guess that if there's a capacitor in the driver's circuit, it's the culprit. Nevertheless, I would advise you to set the more expensive and harder to get green laser diode aside and play with reds first until you're absolutely confident about the circuit/hardware/software.

[Georg]

I got a new idea: to switch between different levels of volt. I addad 2 Ohm parallel to my circuit. I thought the laser may switch between dark and bright. As you see atleast something can be seen now... Also more dots after the other results in a brighter laser light. But is not really nice, because the lines in dark mode a still visible and the brightness of the dots is different.
Red laser is ordered ...
BTW: the 30mW green laser needs aprx 300mA - the 10mW red laser needs 35mA!! Strange - there must be a different physik behind it!

[ElectroNick]

Looking at your last picture, I just had an idea - it may actually be beneficial to show empty lines as dimmer bands of light so that the eye can follow them on the wall and probably better pick up the actual characters on those lines. Perhaps not  as important if the picture is static, but if the text will be changing, and I hope to get to that point eventually, if may be easier to follow.  I don't know, gotta try though.

As far as specifics of green laser diodes (modules?) current - I haven't got one one yet but I would presume that there's not all that much difference between green and red, as in LEDs. (unlike between red and blue / UV - those have different voltage). I think it's just different drivers have different efficiencies. 

[ElectroNick]

Happy New Year to everyone following this thread! 

There has been some progress lately, thanks to the free time afforded by the holidays, so I decided to post an update.

I think I have found the best way to spin that HDD motor! The solution was there all along, I just put it off thinking that others may be easier to implement. The practice, however, showed that quite the opposite was the case. I decided to use the dedicated sensorless BLDC  controller chip that was right there on the PCB of one of the HDDs which I broke apart to get the motor. It was a slightly older, circa mid-late 90s Quantum (I think) HDD, and the IC  Philips TDA5143T was right on its controller PCB, free for the taking. I actually almost thrown it away, I'm glad I decided to look at the PCB second time before throwing it away.

TDA5143T (see attached photos) is a 20-pin SOIC IC. It is very easy to handle because SOIC, although surface mount, is still large enough of a footprint to easily use soldering iron on. I just happened to have a 20-pin SOIC-to-DIP adapter, so I guess you might want to get one if you are using TDA5143T - will make breadboarding easy.

It is very easy to control, only 4 external parts needed - the small ceramic or poly capacitors, value of which defines the RPM and the length of the spin-up period. It starts extremely reliably using its own built-in algorithm and works all the way down to approx 3.5V - important for me because I want to power the entire device from a 5V adapter. Using a 2.5" laptop HDD drive motor you can see on the picture draws about 150mA @ 5W - perhaps it could even be possible to power from USB?

So, anyway, now that I think I got the spinning part of the project done, I got encouraged and created myself yet another 3D model of the mirror holder, this time with surfaces at 1/10° to each other (0.25° surfaces created lines too far apart on the wall 10 feet away). As usual, the model is available from Shapeways here : https://www.shapeways.com/model/1605919

I will continue working on the project as soon as my new mirror holder arrives.