Cannot get TTL modulation to work on flexmod

[DLProcessor]

Im having a bit of trouble getting TTL modulation on the flexmod n2. I applied 5 volts from a regulated ps to the driver. Using my function generator I set a 0-5v square wave signal and applied it to the mod+ and mod- terminals. I hooked up the output terminals to an oscilloscope and observed that there was no square wave modulation at the output (i used a 5 regular diodes in series as a test load). The output is just a regular DC signal.

I tried searching for an answer but came up with nothing. Maybe you guys can help.

[polishedball]

Im having a bit of trouble getting TTL modulation on the flexmod n2. I applied 5 volts from a regulated ps to the driver. Using my function generator I set a 0-5v square wave signal and applied it to the mod+ and mod- terminals. I hooked up the output terminals to an oscilloscope and observed that there was no square wave modulation at the output (i used a 5 regular diodes in series as a test load). The output is just a regular DC signal.

I tried searching for an answer but came up with nothing. Maybe you guys can help.

What is the current on output doing? These are current controlled not DC voltage controlled.

[DLProcessor]

What is the current on output doing? These are current controlled not DC voltage controlled.

The current seems to be constant. I set the curent to 90mA and it doesn't change.

[MisterWilling]

Are you sure you have the solder jumper to select either HIGH or LOW current?

[DLProcessor]

Are you sure you have the solder jumper to select either HIGH or LOW current?

yes I do, its on the high setting.

[catalanjo]

Im having a bit of trouble getting TTL modulation on the flexmod n2. I applied 5 volts from a regulated ps to the driver. Using my function generator I set a 0-5v square wave signal

Just a thought, but maybe your function generator is only for high impedance inputs.
Have you looked to see if your signal is still alive AFTER connecting.

Also you don't mention the frequency of the square wave.

Cheers

[DLProcessor]

Just a thought, but maybe your function generator is only for high impedance inputs.
Have you looked to see if your signal is still alive AFTER connecting.

Also you don't mention the frequency of the square wave.

Cheers

Now that you mentioned that, it could be possible. My output is very small (several mV's). My frequency is at 1khz.

Is there any other way to apply a modulation signal?

[polishedball]

Now that you mentioned that, it could be possible. My output is very small (several mV's). My frequency is at 1khz.

Is there any other way to apply a modulation signal?

Just use some 1.5v batteries series them and you should see current rise as you add a battery.
Why don't you just tie the 5v supply line to the modulation and set peak current with the gain pot?

[catalanjo]

Now that you mentioned that, it could be possible. My output is very small (several mV's). My frequency is at 1khz.

Is there any other way to apply a modulation signal?

I assume you mean mA's since you said it was 5v.

You can buffer it with an op amp (requires PSU), a simple transistor, or use my personal favourite a sensitive opto-coupler. (I like keeping my bits and pieces separate.)

Optocouplers, for some reason don't seem to go down too well on PL so probably best to use a FET transistor.

Good luck !

Cheers

[DLProcessor]

Just use some 1.5v batteries series them and you should see current rise as you add a battery.
Why don't you just tie the 5v supply line to the modulation and set peak current with the gain pot?

If I connect the mod input to a 5v line wouldn't that disable modulation? The oscilloscope that I use only measures voltage. I measured the output using a multimeter and it reads constant current.

Also what is the difference b/w the 0bias and gain pot? Do they have to be set equal to each other? Im kinda new to this. I have to modulate lasers as part of a school project and was recommended to use this driver.

I assume you mean mA's since you said it was 5v.

You can buffer it with an op amp (requires PSU), a simple transistor, or use my personal favourite a sensitive opto-coupler. (I like keeping my bits and pieces separate.)

Optocouplers, for some reason don't seem to go down too well on PL so probably best to use a FET transistor.

Good luck !

Cheers

Well the oscilloscope is measuring output voltage, which is only a few millivolts. Exactly what would be the purpose of adding a transistor? Can you clarify?