Need help with my US circuit!

Discussion in 'The Projects Forum' started by deng1028, Aug 5, 2011.

  1. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    Hi there,

    I'm currently building the circuit for a MB1010 LV-MaxSonar®-EZ1 US, I copied the circuit from the datasheet here http://www.maxbotix.com/documents/MB1010_Datasheet.pdf

    but it seems the circuit is not working properly. I compared the output from the US using my built circuit and the US bought with breakout board and got different output on oscilloscope. Any idea what's wrong with my circuit? Thanks in advance.

    Please find the attach for my circuit design:p

    Cheers,
    Allen
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Well, the most obvious things that jump at me is that you've left the inputs of one of the LM324's channels disconnected. Not so good. Connect the output of the unused channel to its' inverting (-) input, and the non-inverting (+) input to ground.

    The other thing is you're using a different uC, and we have no way of knowing what it's supposed to be doing.
     
  3. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    Thanks I will try if connecting the unused channel would solve the problem~ for the micro controller it just sends out the pings at desired frequency and I've verified that it generates very similar pings as the breakout board. I even tried using the US input from the breakout board to drive the US on my circuit and the output is still different.
     
  4. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    BTW the problem being the output doesn't change at all regardless of position of the US..
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    Is this a 42kHz ultrasonic circuit? Then a lousy old LM324 quad opamp won't work because it has trouble above 2kHz.
    Use an MC34074 quad opamp instead. It has good response up to 100kHz and works fine with the 5V supply.
     
  6. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    but the same LM324 opamp is specified in the datasheet and the US with original breakout board works...unless the datasheet is long out of date lol
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    Maybe a school kid designed the circuit using an old LM324 but without building it or testing it.

    The datasheet shows that at 42kHz an LM324 has a "typical" gain of only 12, and a max output level of only 2.7V p-p. Some weak LM324 opamps are worse.
    But the resistors in the circuit have the first opamp trying to have a gain of 22.3 and the second opamp trying to have a gain of 38.

    The diodes limit the signal to 1.4V p-p so the small output level of an LM324 will be fine but then there is not enough signal to allow the rectifier to function.
     
  8. DickCappels

    Moderator

    Aug 21, 2008
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    When the LM324 came out, I was as thrilled as the next guy, but this is nearly 40 years later, and the we have much better devices now. Please look at more recent devices, and save yourself a lot of trouble. I never really believed that the LM324 was useful past a few hundred Hz.
     
  9. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    Thank you for such detailed info, I'm getting the MC34074PG hopefully it will work :p
     
  10. deng1028

    Thread Starter New Member

    Aug 5, 2011
    8
    0
    Hi there,

    I've tried all the methods mentioned above and still no luck...any help?

    Cheers,
    Allen
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    Do you believe that you problem is confined to the hardware?

    Can you post the program source code?

    hgmjr
     
  12. hgmjr

    Moderator

    Jan 28, 2005
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    Did you post the ultrasonic sensor (US) circuit? If so, I can't seem to see it. All I can see is the ultrasonic detector and the parts list.

    hgmjr
     
  13. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    0
    Here are pics of my circuit:p
     
  14. deng1028

    Thread Starter New Member

    Aug 5, 2011
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    0
    Any help???
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Your photos really don't help much; all of the wires are black, and are all crisscrossing in different directions. it looks like a plate of licorice with "sprinkles" (caps and resistors) on it. About a third of the wires run off the edges of the photos, going to who-knows-where.

    The lighting is not even. The high portion is over-exposed, so there is glare. The lower portion is slightly underexposed, which makes the resistor bands very, very hard to read. Taking good photographs of electronic boards is quite difficult to do indoors. The best possible lighting that you can get is outdoors on an overcast day; as there are no shadows to create harshness; the light is very soft and even.
     
  16. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Could you please update your schematic ? It's confusing. You used the opamp pins 5,6,7 instead of 12,13,14.

    Also, your bypass capacitor C36 is supposed to be connected directly to the IC with short leads. It's not. From capacitor to VEE of the chip it seems to be a long way.

    And
    Can you post the oscillographs?
     
    Last edited: Sep 2, 2011
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