Function Generator Project

Discussion in 'The Projects Forum' started by Axel23, May 8, 2010.

  1. Axel23

    Thread Starter New Member

    Mar 27, 2010
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    Hello all,

    I was hoping someone could help me with a project I'm interested in starting.
    I am looking at building this function generator circuit-
    http://www.free-electronic-circuits.com/circuits/function-generator.html

    I have a couple questions-
    1.It doesn't say anything about this transformer besides the windings. Is this supposed to be used with a 120V AC supply? Can you recommend a transformer?
    2. I would like to use a BNC for the High output and 1/4" for the low output, are there any issues with this?
    3. I also had a hunch to build a counter right after this circuit, would it be best to just use the "high" output into the counter circuit?

    Thank you!
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    I think you will have a hard time finding the 8038 chip.
    It is obsolete and the price is rising.

    Bertus
     
  3. ELECTRONERD

    Senior Member

    May 26, 2009
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  4. Axel23

    Thread Starter New Member

    Mar 27, 2010
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    I did find one chip online, cant tell ya were tho :cool:
    But thanks though.
    Do you have any other recommendations for this though?
     
  5. ELECTRONERD

    Senior Member

    May 26, 2009
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  6. Axel23

    Thread Starter New Member

    Mar 27, 2010
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    I had a harder time finding the MAX038. But I would really rather stick to the schematic, just because I do not have the experience to do the moding.
    But I do not need a real accurate waveform, I am working the in 20-20kHz range, and mostly just need a relatively clean sine wave.
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    The transformer is to make the a lower voltage of the line voltage and provide isolation.
    As stated the transformer has an output voltage of 2 X 6 Volts @ 500 mA.

    If you want to connect a counter, the output signal also goes negative.
    If the counter can not handle this negative part, take care of it.

    Bertus
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Most of, if not all function generator ICs are out of production. Sad but true
    Maybe the XR2206 is still in production
     
  9. Axel23

    Thread Starter New Member

    Mar 27, 2010
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  10. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    You could also go for a wall wart with a dual output.

    Radio Shack has the transformer, though it is 12.6 with a center tap (same thing).

    [​IMG]

    If you can get more than one of those chips I would, you never know when a spare or two can come in handy.

    12V CT 450ma Standard Chassis-Mount Transformer w/ Leads
    Model: 273-1365 / Catalog #: 273-1365 $6.29

    12.6V CT 1.2A Standard Center Tap Transformer with leads
    Model: 273-1352 / Catalog #: 273-1352 $8.39

    The first is a bit under spec, but I think it would work OK.

    To answer your questions:

    1. It is the primary component in a ±5VDC power supply. It can be as shown or an external module.

    2. Sounds good to me.

    3. Yes.

    ******************

    Opps, forgot to mention those were Radio Shack part numbers. Thanks Wookie.
     
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  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    I concur with Bill's recommendation.
    Here's Radio Shack's page on that 12.6v 450mA CT transformer:
    http://www.radioshack.com/product/index.jsp?productId=2103732
    You might find one cheaper online, but the shipping will jack the price up.

    The 7805/7905 regulators should have 0.1uF caps on the outputs to ground, placed right next to them (as close as possible). The inputs also should have 0.33uF caps on them if more than an inch or so away from the filter cap.

    100uF is a bit excessive for the output caps. 10uF should be fine.

    The LF351 is a single-channel version of the LF353, which is electrically the same as a TL082, which Radio Shack carries.

    However, using the LF351/LF353/TL082 will mean that the negative swing of the signal will be limited to -2v. If you want more of a negative swing, you will need to increase the voltage on the negative rail for the opamp, or use a different opamp.
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I seem to remember that the 8038 used in this mode has a non linear frequency v rotation for the set frequency pot.

    Have you considered how you will calibrate this?

    I also seem to remember you could linearize the scale using a constant current into the timing caps.

    I also built one of another approach where the frquency determining pot was replaced by several decade switched resistors. The unit was then linear in terms of period rather than frequency and quite fine resolution could be obtained.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    If he uses a freq counter as the display it shouldn't make much difference.
     
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