Page 1 of 4 1234 LastLast
Results 1 to 10 of 33

Thread: Cannot get TTL modulation to work on flexmod

  1. #1
    Join Date
    Sep 2010
    Posts
    14

    Default Cannot get TTL modulation to work on flexmod

    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.

  2. #2
    Join Date
    Apr 2010
    Location
    Grand Rapids, Mi
    Posts
    2,433

    Default

    Quote Originally Posted by DLProcessor View Post
    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.
    leading in trailing technology

  3. #3
    Join Date
    Sep 2010
    Posts
    14

    Default

    Quote Originally Posted by polishedball View Post
    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.

  4. #4
    Join Date
    Jul 2009
    Location
    Dallas, Tx
    Posts
    372

    Default

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

  5. #5
    Join Date
    Sep 2010
    Posts
    14

    Default

    Quote Originally Posted by MisterWilling View Post
    Are you sure you have the solder jumper to select either HIGH or LOW current?
    yes I do, its on the high setting.

  6. #6
    Join Date
    Aug 2010
    Location
    London or Spain depending on the weather
    Posts
    1,381

    Default

    Quote Originally Posted by DLProcessor View Post
    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

  7. #7
    Join Date
    Sep 2010
    Posts
    14

    Default

    Quote Originally Posted by catalanjo View Post
    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?

  8. #8
    Join Date
    Apr 2010
    Location
    Grand Rapids, Mi
    Posts
    2,433

    Default

    Quote Originally Posted by DLProcessor View Post
    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?
    leading in trailing technology

  9. #9
    Join Date
    Aug 2010
    Location
    London or Spain depending on the weather
    Posts
    1,381

    Default

    Quote Originally Posted by DLProcessor View Post
    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
    Last edited by catalanjo; 09-14-2010 at 04:07. Reason: FET = less current required.

  10. #10
    Join Date
    Sep 2010
    Posts
    14

    Default

    Quote Originally Posted by polishedball View Post
    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.

    Quote Originally Posted by catalanjo View Post
    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?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •