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Laser Driver TTL confusion.

StuartB

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Hi.
May be it's my age but I'm a bit confused with a laser diode driver I just bought.

This is the one:
enhance


In the image on the left it shows "TTL -" on the bottom right pad of the board next to the Laser Diode "-"

In the image on the right it shows the back of the board and shows "TTL -" that appears to be shared with the GND connection of the power input (5Volts + and GND).

What I don't understand is why are there 2 connections for the "TTL -"

When I connect a multimeter set to continuity, the 2 different pads are not connected.

Any ideas about this would be really helpful.
 



paul1598419

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This looks like a cheap Chinese driver used mostly to drive pump diodes in 532nm DPSS lasers. It is likely a typo. I would check to see that the +5 volt supply and the positive LD pad are continuous. They should be if I am right. If not, check to see if the negative supply side and the negative for the LD are continuous. If that is the case, then the driver is not to pump 808nm diodes for 532nm lasers. Regardless, the negative supply should be the negative for TTL. Forget about what else they claim it is.
 

diachi

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Hard to know for sure, but my guess is that one of the images is rotated 180 degrees. So the "top" on one image is the "bottom" on the other.
 

lasersbee

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Try using a DMM and check for continuity
between the pins. The (-) indications may
be tied together. Hards to tell just by the
pics.

Jerry
 
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paul1598419

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Hard to know for sure, but my guess is that one of the images is rotated 180 degrees. So the "top" on one image is the "bottom" on the other.

That was my impression when I first saw these two together. I'm pretty sure this is correct.
 

StuartB

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Hard to know for sure, but my guess is that one of the images is rotated 180 degrees. So the "top" on one image is the "bottom" on the other.

That's correct but irrelavent really. As I am more concerned about why there are 2 "TTL -" pads, and not the orientation of the images.

I would check to see that the +5 volt supply and the positive LD pad are continuous.

They are continuous, but the "-/gnd" for the supply and the "LD -" are not.

I also found the description for the Board:

Laser diode driver board
Voltage: 5V
Current: 50-300mA (Can only drive power at 20-200mw, less than 10mW will burn the pipe)
Suitable laser Diode: 50-300mW 660nm 780nm 808nm 850nm 980nm
Tips: if you do not need TTL function, you need to short circuit power"+",and TTL"+"
 

paul1598419

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Since the positive supply is continuous with the diode's anode connection, my first idea of what this driver is was correct. It is used to pump 808nm diodes for cheap 532nm DPSS lasers. I have never know these drivers to have a TTL input and am skeptical that this one does now. If it does use a TTL input, it will likely have two pins for it. A negative one and a positive one. Since the regultaion takes place one the negative driver side, you likely can't use that as you negative pin for TTL. I still doubt the TTL input on this driver, but if it does exist, you will need to use the two pins to make it work.

It seems they are saying the - TTL is the positive source for the driver. Then, you will need apply an additional +5 volts to the +TTL with respect to the +5 source for the driver. In other words, you can't borrow +5 volts from the driver to activate the TTL.
 
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StuartB

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Ok Paul, thanks very much.

I was thinking it would just connect to an Arduino running GRBL with the TTL+ connected to pin 11 on the Arduino which would supply the 0 to 5v PWM signal,
and the TTL- connected to a Ground on the Arduino, using the seperate TTL- pad on the driver board and not the one shared with the GND of the supply for the board.

I may just give it a miss, as I'm not so sure now..

Thanks for the help.
 

10fenny

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Looks like an aixiz driver clone! Ide check the pinout on those
 

Benm

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This is a really odd board. Putting one side rotated 180 degrees doesn't help make things easier to understand, but looking at it it seems:

GND and TTL+ are the same pad on opposite sides of the board but probably connected by a via.

TTL- is connected to the feedback photodiode pin of the laser diode, which is likely to be just a 'not connected' pin.

I can't really make out the traces from the photos, but looking at the components this is a low side driver (i.e. the driver is between the laser diode cathode and ground) based on a LM358 opamp, and some power transistor on the opposite side of the board.

But there a lot of stuff on there that would not make any sense if there was no TTL or modulation input. There seem to be 3 small signal transistors or (dual) diode packages on there, which would not be needed without modulation input. One of them may be just a polarity protection, but the other 2? Perhaps 1 is used in a darlington configuration between opamp and power transistor, but that should really be all for a driver with no modulation input.

Perhaps they've designed it in a really odd way where you can modulate it, but not with a signal that shares ground with the laser power supply. This would be very impractical, but possible if the laser runs off a separate power supply or batteries independent of the control signal.

By why they'd use the feedback diode pad as an input boggles me - i'm afraid this is chinese creativity and i would not trust it as far as i could throw it.
 




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