How to pulse a laser?

I find a fairly simple explanation:
How to Increase the Power of a 555 Timer Circuit | eHow.com

co0l video, stickying the thread

scopeguy20 said:

I am hopeful to get pulse rates from 120Hz to 1200 Hz with a lot of interest near 530Hz the current w/b about 650ma as with the 635nm 300 mW it is about the limit. -Glenn

Click to expand...

No problem with the frequencies, this circuit can do 2Hz to 2Mhz. You set the frequency range with R1, R2, R3 (pot), and C3.

rhd said:

I find a fairly simple explanation:
How to Increase the Power of a 555 Timer Circuit | eHow.com

Click to expand...

I don't use the 555Timer to directly power the driver - a 555 can only source/sink 200mA tops, and you're going to run it in to the ground that way. You feed it in to a switching transistor which bears the load of your load. The 2N222A can handle 600mA tops. Basically if you stick to any NPN BJT or MOSFET this will work, you just select your transistor by the Ic max for your load.


I'm writing up the schematic now. I'm throwing in some bells and whistle such as variable pulse frequency, because I want this to be an all purpose and easily modified schematic. Obviously my protoboard one was restricted by what I had on hand.

When it is done I will reply/edit it in the thread.

---

Update: Finished up the schematic, feel free to ask any questions.



High res version:
http://www.box.com/files#/files/0/f/93282141/1/f_1459799287


Video with fog:


Edit: I noticed and errant trace in the 555Timer IC's Thr to Dis resistor string. It has been corrected. Make sure you get rid of the incorrect files - file names are the same.

You can pulse the laser by goung to the on seitch and rapidly hit on and then off

^.^ thanks Sigurthr, cant wait to try this out later tonight

One question I have -

We get a square wave out of the 555, but does that translate into a square wave after the DDL ?

EDIT: Two questions -

Why does the VCC need to be: Vf + V Drop Out + 3V ?
Is the NPN dropping 3V? Because the 555 itself shouldn't be dropping anything in the diode's path (should it?).

You need a resistor in between the 555 pin #3 and the base
of Q1. The 2N2222 is not a FET.
Diode D1 is not required...

@RHD the 555 is not in the load circuit. It is only turning Q1
on and off. The only thing in line with the LD is the LD Driver
and Q1..


Jerry

rhd said:

One question I have -

We get a square wave out of the 555, but does that translate into a square wave after the DDL ?

Click to expand...

That depends on any capacitance you have in the DDL driver. The transient protection caps can often spoil your ability to modulate very fast since these caps act to smooth out the waveform.

It had occurred to me in the past to try directly modulating an LM317 either via the input as you see here or by modulating the adj. pin but I never did try it.. don't know why I didn't actually. Maybe I'll try it out yet.. who knows?

The filtering caps for the DDL do smooth out the waveform, I'd recommend a smaller value filter cap for higher frequencies, and even then it may be more sine than square. Since it is still constant current protected it shouldn't cause any real problems as long as the voltage is high enough, which is part of why I went for 3V extra. True TTL squarewave modulation has to be done directly to the output stage of the LM317 and not it's input power or done without filter caps and with other transient suppression. You don't want to cut the power to the diode though because it will unload the LM317 and potentially fry things.

The NPN does appear to drop voltage, but I haven't determined how much yet - 3V extra solves it though. My breadboard is fed with 8.2V, which is 3V (LM317) + 0.7V (1N4003) + ~2.75V (LD Vf) + NPN drop out (maybe 1.5V? two junctions, makes sense) + maybe a few decivolts extra. I don't have an incrimentally variable power supply so I can't test the input lasing threshhold voltage to determine the NPN dropout curve. I can't measure the NPN drop out across it like you would a passive device because my multimeter isn't fast enough to respond, I would need an oscilloscope. The 555 does not drop any voltage and only consumes a few mA.

Yes, it would probably run better with a 1k Ohm resistor between the Base of Q1 and the OUT (pin 3) of the 555, but it isn't 100% needed at low frequencies as the input impedance of the 2N222A is pretty high. You could add a small value series nonpolar capacitor as a DC blocking cap as well. You can also reverse the Collector and Emitter connections on Q1 and it wouldn't affect the performance. I left this semi-barebones for simplicity and cost. I can modify it further if needed for any particular goals.

I always put series protection diodes in my drivers for reverse protection and to help reduce over-voltage chance. I dislike parallel shunt reverse polarity protection because if the diode ever gets destroyed by overflow it will leave the rest of the circuit vulnerable. Placing it in series effectively cuts off the rest of the circuit should it fail. Sacrificial diodes FTW. Also, I tend to run my modules off 12V (or 13.8V) so they need extra voltage sinking if they aren't 450s or 405s (5V Vf + 3.7V DDL and Series Diode + NPN drop + more diode shunts/clamps if needed). I left the DDL driver seperated from the pulse circuit on purpose for this reason, it isn't a mandatory part, just a bonus for anyone who might need. This circuit should work for all drivers at low pulse rates, high pulse rates may interfere with boost/buck drivers (I don't know if it will though!).

I was bored so I drew up the 555 pulse circuit (I hope that Sigurthr won't mind) in Eagle and designed a pretty SMD board for it - it is 1.5x0.7 cm and the pot is 5 turn.




Eagle BRD and SCH
pld-01.brd
pld-01.sch

Oh wow! Very nice, I don't mind at all, in fact I'm honored!

Is anyone else getting an "invalid data" error for both the SCM and BRD files?

I made them using Eagle 6 (new XML data format), so if you are opening them in 5, you are probably gonna get an error. I'll try to reupload them in a new format.

Johnyz said:

I was bored so I drew up the 555 pulse circuit (I hope that Sigurthr won't mind) in Eagle and designed a pretty SMD board for it - it is 1.5x0.7 mm and the pot is 5 turn.

Eagle BRD and SCH
pld-01.brd
pld-01.sch

Click to expand...

You might want to correct that...
just the SMD 555 wouldn't fit on a board that size...


Jerry

I'll correct it right away...
Maybe the bare chip from inside the package could fit...

You can pulse it using an Arduino and a 2N2222.
it has been discussed in this Forum. Here is the link:
http://laserpointerforums.com/f67/how-drive-green-laser-using-arduino-70770.html
There are some easy schematics down the post.
Also you can program the Arduino to pulse at the rate you want.
I would be happy to help if you want.