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Analog domain problems

Discussion in 'Microcontrollers, Programming and IoT' started by saurabh17g, Apr 26, 2010.

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  1. saurabh17g

    saurabh17g

    72
    0
    Mar 8, 2010
    Hello, I used AD9833 to generate waveforms. I have created 3 types of waveforms and they are selectable by a switch. It worked fine for one week and I was getting sine, triangular and square waves upto 5MHz comfortably. Now, I am facing strange problem.I am able to get square wave but sine and triangular waves are not comming.
    I have not changed the microcontroller program that generated the all the waveforms since 7 days. I am debugging the hardware since yesterday. Not able to find the exact reason.
    I have checked the voltage at pin no.1(comp) of AD9833. It is 5V. Is it correct?
    I have attached screen shots of DSO. first is square wave and 2nd is sine and triangular wave(same output for both the waves). Third ts circuit diagram.
    Pls help me.
     

    Attached Files:

    Last edited: Apr 26, 2010
  2. saurabh17g

    saurabh17g

    72
    0
    Mar 8, 2010
    the IC requires 20mW power.

    according to datasheet

    i have a powersupply of 5V

    transformer rating-> 1 A

    so, 7805 output will be in maximum current i.e 1A according to datasheet

    i connected this supply as i have to drive multiple applicatoions

    so it should not get loaded

    currently, i have microcontroller, LCD and Ad9833

    running on that power supply

    20mW = 5 x ?

    so max current requirement is 10mA

    my powersupply will provide much more than 10mA

    i saw some tantalum capacitors becoming BROWN

    so, is it the reason that sinewave and triangular wave not comming?
    but these capacitors are connected between powersupply and ground. So, still do not know as how much critical aspect do they play in actual circuit. And there are disc ceramic capacitors as well doing the same function.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,305
    2,738
    Jan 21, 2010
    Check that they have a sufficient voltage rating and are not connected backwards.

    Are you confident that you have the experience to complete your project?
     
  4. saurabh17g

    saurabh17g

    72
    0
    Mar 8, 2010
    I am not able to trace the exact reason as to why the sinewave and triangular waves are not comming. This should not happen after I complete the project and it stopped working after a week. Doesn't it look strange. also, the fact is these capacitors are connected between powersupply and ground. So, still do not know as how much critical aspect do they play in actual circuit. And there are disc ceramic capacitors as well doing the same function attached parallel to tantalum capacitors. Pls check the circuit diagram in the first post.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,305
    2,738
    Jan 21, 2010
    Can you tell me:

    (1) what the voltage rating of the tantalum capacitors is, and
    (2) how you determined which lead is the +ve lead, and
    (3) can you confirm it's connected the right way around?
     
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