Need to amplify this

[FireMyLaser]

OK, two things:

To prove my ignorance: I can't download the file and what is "Line in"?

 

[rog8811]

I will have a look at the download page when I get in from work tonight.
Most sound cards these days have 3 jack sockets
speakers,
microphone,
Line in

Line in is for connecting other audio devices.......

Regards rog8811

 

[Zom-B]

I think your setup is not going to work.

I think the only way is to convert PWM to a variable voltage using a simple Low-Pass Filer (LPF ) and using a precision power voltage-to-current converter with slope limitation to drive the laser. (I can give you a schematic once I get home, but I can say it will involve over a dozen parts including a CA3140 opamp IC and a power darlington with heatsink) Or just use a current limiting resistor as poor-man's voltage-to-current converter.

Do you think you're up to it?

 

[FireMyLaser]

I think your setup is not going to work.

I think the only way is to convert PWM to a variable voltage using a simple Low-Pass Filer (LPF ) and using a precision power voltage-to-current converter with slope limitation to drive the laser. (I can give you a schematic once I get home, but I can say it will involve over a dozen parts including a CA3140 opamp IC and a power darlington with heatsink) Or just use a current limiting resistor as poor-man's voltage-to-current converter.

Do you think you're up to it?

Please continue.

 

[Zom-B]

Sorry , I did not have time yesterday, and today is the same story. The only thing, I realized the current limiting resistor idea is never going to work because the LPF can never supply more than a couple of mA. It would need a power voltage follower, consisting of an opamp (any cheap one) and a power transistor with heatsink. With this, one might as well built the before mentioned converter with only a few extra basic parts.

I found some time to draw a schematic at school. No guarantees.
If both circuits are supplied by the same source, or if your gadget is powered by batteries, no opto coupler is necessary.

 

[FireMyLaser]

Hey nice, I'd like to give it a try! I have some questions fore you:

Are you sure that this circuit (times three) will work with my RGB-IC? It has common anode, the pulse is on the cathode(s).

I have no experience with OP-amps so I need to know how to identify one on scrap circuit boards because that's my only sourse of components atm. The same for the darlington.

 

[Zom-B]

I think this curcuit should work. It is a slightly modified version of my adjustable DVD laser driver.

It was hard finding a solution to the common anode outputs. I inherited the opto coupler idea.

Just build the supply once (upper part) and the driver three times.

Depending on the PWM frequency of the rgb chip, you might have to change the filter cap.
Depending on the laser, you might have to change the 180k divider resistor to get maximum output current right. Always use a test load when adjusting or replacing things. (your amperemeter is a good test load, no diodes/leds required )

Identifying the CA3140 is easy, it is an 8-lead DIL with CA3140 written on top.
The Darlington is a bit trickier, as you'll have to look up all the part numbers of heavy transistors you scrapped, and check the properties.

 

[FireMyLaser]

OK this is hard, but I'll try to find the parts and see what happens. I don't even have a breadboard!

Thank you very much for the schematic.

 

[rog8811]

*has noted the circuit and is looking for the parts to build it*

 

[FireMyLaser]

Amazing! I found a CA3140 OP-amp in a matter of minutes!

But how do I know if the transistor is a darlington, there are so many of them on the boards/junk boxes! Too many.

 

[FireMyLaser]

I have a bunch of TO-126 packages too. Any chanse that any of them will work?

I've tried ~30 (I have more) different TO-220's and not even one of them was a darlington. *ARG!*

 

[phenol]

look into TIP110; it is a commonly spread darlington NPN in TO-220 package.

 

[FireMyLaser]

Ok this is all I got that might work. Unfortunetly I can't read the datasheets with my loan computer.
I also failed to the find LM7808 reg, but I have all the OP-amps I need + some CNY17-3 optoisolators.

1x TIP42A m8601 (no data sheet)

2x 4x BD645 http://www.alldatasheet.com/view.jsp?Searchword=BD645

2x BF869 http://www.alldatasheet.com/view.jsp?Searchword=BF869

8x BUX86 (TO-126) http://www.alldatasheet.com/view.jsp?Searchword=BUX86

1x 2x IRF520 http://www.alldatasheet.com/view.jsp?Searchword=IRF520

1x BD679A http://www.alldatasheet.com/view.jsp?Searchword=BD679A

1x SEC E13009 http://www.alldatasheet.com/view.jsp?Searchword=E13009

 

[Zom-B]

The BD645 looks usable. A BD679A with TO-126 packakage is far too small. (as depicted in my image, even the totally plastic TO-220FP package will proably be inadequate)

Another thing, I don't know if the 4.7K resistor for the opto coupler is the right value, and if the voltage it creates is linear to the input PWM. I guess the resistor depends on both the h[sub]FE[/sub] of the opto coupler and the input voltage.

 

[FireMyLaser]

Well, in that case I have all the parts I need except from the regulator. I have some 5V's (in TO-220 packege) but that isn't enough, right?

I'm going to try it anyway tho. Stick around, this won't take long.

 

[FireMyLaser]

Nothing happens. I've double checked the circuit and it looks ok. I don't know what the pot does, but nothing happens when i turn it.
The only different thing with the my circuit is that I use a 5V regulator and instead of a 180Kohm I use a 220Kohm. The ddl driver drives a red high power LED, but it doesn't light up at all. I get 0V at the ddl driver, I use 12V to power everything, I get 5V to the OP-amp, and the RGB circuit works.

Dead end...