Help replicating signal

Discussion in 'The Projects Forum' started by eetjd, Jun 2, 2015.

  1. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    Hello everyone! This is my first time posting here, my name is Justin.

    I need help replicating a signal on a system I'm currently working on. The line, when idle, sits at +8VDC; when the line is active, the system transmits data on the line by modulating it and creating a very rough sin wave. The voltage swings from about +5.5V to about 9.7V when it's transmitting. The wave has a period of about 8uS so that gives it a frequency of 125k HZ. I've included two pictures of the line when it's active; the data was captured using a logic analyzer that can do analog.

    What circuit could I use to replicate this signal? Should I use transistors, OP AMPS or something else? I'll admit I'm somewhat weak in analog circuits, so this is a learning process for me.

    Thanks for you time!

    signal_snip.PNG
    signal_snip2.PNG
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The basic circuit is dirt simple. Keying the 125kHz on/off without introducing a "thump" is where the fun begins. This shows that the load resistance at the far end must be high, or the 8V source must be adjusted. See the slight offset between green and violet?
     
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  3. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    Hi Mike, Thanks for the reply!

    They are running the signal through a series of OP AMPS and then some Comparators before going to the microprocessor.

    Is there a way of doing this without introducing an AC generator? In the circuit they seem to using only transistors, caps, diodes (schottky and zener) and MOSFETs. I've tried replicating the circuit in Multisim but didn't get no where near the same wave pattern.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    What is the load imedance, circuit type, etc? Is the 8 V delivering power as well as data? If so, how much. What power is availale for your replication, +12 V only, +/- 12V, etc? The signal looks like on/off keying of a 125 kHz carrier, riding on DC. Depending on the load, this can be done with a power opamp summing the keyed carrier with a DC offset.

    ak
     
  5. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    Hi AnalogKid, thanks for the reply!

    The line is delivering power to the external component. I should have mentioned it delivers +10VDC and that is idles at when the component is not selected. When the component is selected but idle (not transmitting data) the line idles at +8VDC and then it's transmitting, the voltages swing from about 5.5V to 9.7V. I would like stay with the +10VDC power only. I attached a schematic of the circuit generating the signal. Power comes in on the J1-1 pin and this is also the pin the data comes out on.

    CIRCUIT.PNG
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Can you show us the existing circuitry? The "AC generator" as you call it, is the oscillator, clock source or whatever makes the 125kHz carrier. I was assuming you already had that. What exactly are you asking for?
     
  7. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    I'm looking to replicate the signal that is generated by the circuit drawn in the schematic I posted in reply to AnalogKid.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What type of signal does the micro-controller put on U5-19 and U5-11?

    The output is J1-1? What connects to the other end of that line?
     
  9. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    Yes, power comes in J1-1 and the data also comes out J1-1. The line connects to the collector of a PNP transistor. I'm not sure what signal the micro controller is putting on U5-19 and U5-11, I haven't used the logic analyzer on those yet.
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    This is hopeless unless you know what is externally connected to J1-1 (presumbably, that is what your home-brew circuit has to drive), and what the microcontroller does with those other two signals.
     
  11. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    Here is the entire circuit as given to me (I didn't draw it out, someone else did). On page 4, U45 is the microprocessor it goes back to.
    circuit 1.PNG circuit 2.PNG circuit 3.PNG circuit 4.PNG
     
  12. eetjd

    Thread Starter New Member

    Jun 2, 2015
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    Bump to the top. Anyone have any ideas or suggestions?
     
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