DC offset of a sinewave

Discussion in 'The Projects Forum' started by cade007, Apr 18, 2006.

  1. cade007

    Thread Starter Member

    Apr 14, 2006
    14
    0
    Is there a way to create an offset voltage for a sinewave output from the NTE864? I want the sinewave to oscillate at 60 Hz from about 1.1 V to 3.1 V. I could probably adjust the amplitude with a simple voltage divider and I was thinking I could create the offset using an op amp as a buffer with the rails at 1.1 and 3.1. Is there any op amps that would work for this job or is there a better way to do this? Any suggestions?


    http://pdf1.alldatasheet.com/datasheet-pdf...NTE/NTE864.html
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    I put a schematic of an 8038 circuit on this message. Increasing the size of the timing capacitor will get you into the 60 Hz range pretty easily. The sine output is very current limited, so the total 100k load is about right. Just about any old op amp will do for the buffer. The one trimmer will adjust the waveform amplitude, and the one on the non-inverting input will let you set an offset.
     
  3. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
    You could pass it through an OP amp and set the input bias to 2.1V. That would make the O/P swing around 2.1V. I would use a supply of +5V as trying to do it with 2 rails of 1.1 and 3.1 would be a bit difficult. You would need a very good rail to rail OP amp.
     
  4. cade007

    Thread Starter Member

    Apr 14, 2006
    14
    0

    Thanks that looks like it will work perfectly. The only question I had was why is the resistor R8 there? Doesn't the variable pot act like a voltage divider anyway? R5 as well? Thanks for the schematic.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    R8 is there to keep up the load resistance for the weenie sine output. I was interested is setting the level to 1 volt, and used parts available. A 100K pot would work just fine by itself.

    The modulation voltage range is from Vcc to some fraction of Vcc, so R5 limits the lower voltage you can get to with the trim pot.

    If you use 1 mike for the capacitor, you will probably be able to get down to 60 Hz.
     
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