Christmas Ornament with 650nm laser

[alessnilsen]

Hi! I'm interested in make a different Christmas Ornament, this time with a 650nm laser!

My aim is to produce many dots of light using a rotative difraction grating and a astable oscilator to make the laser blink and rotate the diffraction grating.

I decided make the astable circuit with two relays, one SPDT and one DPDT, the circuit is:

This works like a charm, generating a switching frequency with aprox. 50% duty cycle, but when I connect my driver on it, the LD dies! :yabbmad:

I've been thinking, my driver have a 33uF protection capacitor in parallel with the LD, I've put protection diodes in parallel with each relay coil. My LD runs in 400mA. Why are my LD's dying?

 

[Cyparagon]

You know you can make an oscillator more cheaply, reliably, and efficiently with solid state, right?

Is the driver rated for 12V? I doubt it. I don't think relying on that 25 ohm is good enough here. What are you using for a 12V source?

 

[alessnilsen]

Yes, my oscilator died too, maybe because charging a big capacitor 3x per second cause excessive sparking.

25 Ohms is the value to the LED work in the simulator, the driver is a LM317, rated as 415mA (3 Ohms). The 12V supply is standard outlet adaptor.

So, I will start all from scratch using a LM555.

 

[Cyparagon]

Get rid of the 25 then. The LM317 will drop the extra voltage as needed. Try powering it directly from 12V to verify it works without the switching. What is the voltage across the 3 ohm?

 

[alessnilsen]

No, forget the 25 ohms resistor! I put it into the scheme to see if the led blinks, really worked, but my DPDT relay stopped switching one of the poles, resulting in the SPDT relay to stop.

The voltage across the 3 Ohms resistor is 1,25V.

What is better to switch? Relay or transistor? It will make any difference since is a LM317 driver?

 

[Leodahsan]

@alessnilsen
In your application it won't matter at all, I'd personally use transistor because they won't... "click"?


a good reference regarding 555s (calculators, click to see astable timers):
LM555 Timer Circuits

Regarding the link above:
Just adding a transistor (base) to pin 3 (with a resistor of course), I would build the whole thing like:

1 - Using a small value resistor, so the transistor behaves like a "relay" like you said, and limiting current to the laser diode with a resistor (no driver). This would work fine if the diode is well heatsinked and the power supply is fixed voltage (ie. no batteries)

2 - Transistor in amp. mode, calculating Ic = Beta*Ib, would behave as a rudimentary driver. The main drawback, is that the Beta (transistor gain) would vary with temperature, so it would need to stay COOL.

If you're not into electronics, just want the whole thing working as simple as possible, use the double relay schematic + lm317 DDL driver.

If you want more help (portuguese) or didn't understand my post at all, I can translate all of this and PM you.

:beer:

 

[alessnilsen]

Thanks! The click click sound of my astable is like a clock, tic tac tic tac ... Only 5 min listening this and i'm getting crazy! :na:

I must check if the LD is well heatsinked, I'll use a dead laser module as housing, remember, the laser will be on only 50% of the time.

 

[Leodahsan]

Yeah solid state would be better than relays then. BUT you must check the laser operating temperature...

 

[alessnilsen]

My test of the LD temperature failed, the module becomes too hot. But the bad news is that my module is pressfit, so, there's no simple way to extract it without damage.

 

[Leodahsan]

The module, or the diode is pressfit? I've removed long open cans from pressfit modules without issues, using an antenna + vice.

 

[alessnilsen]

I extracted the LD successfully using the metal brackets of the DVD sled. I don't know, this LD heats up more that others that I used, maybe because is from a 18X burner, so I putted it into a bigger heatsink.

I assembled the 555 astable using a DPDT relay, with 20% duty cycle, so, each time the laser is on, it projects a different pattern.

 

[alessnilsen]

All working! Thanks for the help!