Making TTL driver for DX 200mW greenie

Would it be possible to use this driver for strobing DX 200 mW greenie fast enough to get a decent picture/animation with any 30kpps scanner?



I just put in an order for 2 of those DX modules and I hope that I don't have to figure out a driver of my own (wish I could but I thought I'd ask here first...)
I've tried search function but it really doesn't give me any useful answers.
Btw, laser driver will be powered by +24V so that's why I got interested in this solution with LM317 as VOLTAGE regulator.

Your scematic does not provide current regulation, only voltage regulation. Search the forum for schematic of LM317 current regulator. For 24V operation, I would use 2 LM317. The 1st to provide voltage regulation to approx 4V, the second to provide current regulation to suit your LD.

Also, it is not wise to switch the LD like you show, instead use the NPN transistor to shunt (short) out the LD. The current reg will barely see a difference.

Since the DX module already has current regulation I wouldn't need any current regulation on the switching driver.
It only needs voltage regulation down to 3V for the DX module and laser module takes care of the rest. But as you mentioned shorting out LD with NPN would probably be the easiest way of achiving strobing.

I guess I will only use LM317 as ordinary voltage regulator since for example 7905 voltage regulator doesn't seem to like as high voltages as +24V (it only regulates it to abt. 8V or so...)

Thanks for the answer!

Freitsu said:

Since the DX module already has current regulation I wouldn't need any current regulation on the switching driver.
It only needs voltage regulation down to 3V for the DX module and laser module takes care of the rest. But as you mentioned shorting out LD with NPN would probably be the easiest way of achiving strobing.

I guess I will only use LM317 as ordinary voltage regulator since for example 7905 voltage regulator doesn't seem to like as high voltages as +24V (it only regulates it to abt. 8V or so...)

Thanks for the answer!

Click to expand...

I killed a 10mW green last night, that had it's own current regulation by TTL modulating the 3V input... It did not like it for some reason...

Those modules are not planned for become drived with pulsed input, especially at high frequencies.

You need to draw the schematic of the driver, and modify it for add a TTL input.

Do you have any schematic of the driver ? ..... or, at least, decent pics of these drivers, front and back, for see if is possible to take the schematic ? ?

I took the schematic of the driver from a 100mW DX module some months ago:


P.S.: I was working on a PWM enabled version of this schematic but the drawings are buried somewhere. I'll try to find them.

FYI, the full part numbers of the semis are:

LM358 op-amp
2SD882 NPN transistor

Good circuit!

lazerov said:

I took the schematic of the driver from a 100mW DX module some months ago:

P.S.: I was working on a PWM enabled version of this schematic but the drawings are buried somewhere. I'll try to find them.

Click to expand...

I would appreciate it very much if you found them and posted them!
Others might have some use of the drawings aswell...

This is a standard current source schematic.

You can add a TTL modulation to it in 2 ways ..... placing a transistor between the ground and the point where the 20K (R2) resistor and the 10K (P) trimmer are connected together ..... not the better, but this is the more easy way for do this ..... if you can also substitute the 10uF capacitor with a more low value one (like 100nF ceramic), is also better.

You can use the transistor inside the optocoupler, without any other component from this side, for so low currents ..... the emitter go at the ground ofcourse.

Another way is also better, but it require that you rewire the other op-amp inside the 358 chip, and this is too much complicate for a hobby-level work.

EDIT: remember that this is a "turn-off" modulation ..... when you give the TTL signal, the module turns off.

This is the conceptual schematic:


Red graph is the input signal, orange - output.

D882 (or 2SD882) wasn't in the component database so I substituted it for BCP68.
BC847A could be substituted for any general purpose NPN transistor.

There probably should be added some capacitors. There were 2 in the original schematic, but I had to remove them because they were causing problems.
As I said, this is only a conceptual simulated design, so any input from somebody more knowledgeable is appreciated.

EDIT: Connecting the Q2's collector to the point between the 20K resistor and the trimmer, as HIMNL9 said, is the better option.

@ lazerov: the concept is good but the application can cause some problems, if the current is low ..... taking away the Vref from the source point is better, at this level, cause it grant you a more "zeroed" output, when triggered (also if this can also not be important, with a green module)

But also this solution can work.

Thanks alot, lazerov!
I will do some experimenting with your schematics once the module arrives.

+rep for you!

Just as suggestion, place a 100K resistor between the base of the transistor and the ground, for avoid that some disturbs can turn off your module when the TTL input is left opened

Freitsu said:

Thanks alot, lazerov!
I will do some experimenting with your schematics once the module arrives.

+rep for you!

Click to expand...

Thanks!

I strongly advice you to use a test load (2x 1N4001-1N4007 diodes) in case something goes wrong.
An oscilloscope, if you have one, would be very useful for monitoring the output waveform.

HIMNL9, pulldown resistor isn't that bad idea actually...

I will check the output signal with my vintage 20MHz o-scope before connecting LD

lazerov said:

This is the conceptual schematic:

EDIT: Connecting the Q2's collector to the point between the 20K resistor and the trimmer, as HIMNL9 said, is the better option.

Click to expand...

Actually, connecting Q2 over the TL431 is an even better option in terms of 'lowest off current' achieved. You always have the C-E voltage drop of the transistor to consider, which is a few 100 mV typically in saturation. If you connect it over the voltage reference, that would result in a difference between on and off currents by a factor of 10 or so.

This is more then sufficient to get below the pump diode treshold, and surely below what the crystal set needs to provide any green light.

I'd also suggest running the whole thing with a 5 volt power supply so the LM358 has some more room to work with, substituting R6 with a slightly larger resistor (2k2 or so).

Also: put some decoupling capacitors on the power rail, so the current draw from the laser diode doesnt mess with the reference voltage. I'd suggest 100 uF and 10 nF in paralel or something similar.


The concept in gerenal will surely work - i've build several very similar drivers, but used ttl to pull up on R6 instead of using a transistor to shut down the voltage reference. This results in reversed behaviour, in the sense that the laser will then turn on only when a TTL signal is applied. Most laser show software allows invert-blanking so both solutions will work in real applications.