Hall Effect sensor stops detecting magnetic field when using seperate battery

Discussion in 'General Electronics Chat' started by Jayvin, Mar 23, 2015.

  1. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    Hello guys, i am building a small project on cable location where i have a transmitter and a receiver which works on 1kHz. When i was testing the system, i was receiving my signal on the hall effect. Now when i connected the hall effect sensor and transmitter to the different sources, the hall effect sensor stopped capturing the signal.
    Could you please help me understand why this is happening?
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Which HAll sensor (model number)?
    Please post your circuit diagram.
     
  3. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    Actually its an Allegro 1302 http://www.allegromicro.com/~/media/Files/Datasheets/A1301-2-Datasheet.ashx

    I was testing the output directly from its output pin. When the transmitter and receiver were working using the same source, the signal was present and when i separated the source. It stopped.

    The transmitter circuit is something like this where the load is in series with a small cable.
    [​IMG]
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    I don't get the transmitter/receiver part. We are not talking RF right, or do we? How do you transmit? Light, wireless 1kHz on a carrier? with wire? What's the power supply? What voltage etc. As many details as possible, otherwise we are guessing. You can also post a photograph of your setup.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    if you are scoping the signal, then it may just be the fact your two power circuits have no 'common' in common.
     
  6. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    Let me explain the project. My goal is to design a cable locator. Cable location normally works by injecting a signal with a unused frequency (in this case 1kHz). Now i have to design a receiver that detects the 1kHz signal and compares it on a microcontroller. My problem is on the signal side.

    I have designed the transmitter being a low side mosfet switch which is powered by a 12V battery. I have a current limiter resistor in parallel so that i can adjust the current flowing in the cable, thereby controlling the Electromagnetic field generated around it. ( This part seems to be working fine)

    Now the receiver should have a sensor that can detect the field and send it to an Arduino. When i was doing the preliminary tests, the hall effect sensor captured the signal and gave me a 1v pk-pk with a dc offset of 2.5V which is fine. Now for the test both the transmitter circuits and the sensor was powered from the same power source along with 5V regulator for the sensor. On seperating the transmitter using a 12V battery and the hall effect from the previous power source. I seem to have lost the signal.
     
  7. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    How can i common two power sources which should be isolated and would be far from each other. Even if the ground is the common, shouldnt a hall effect sensor just measure the magnetic field?
     
  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Must be some kind of wiring problem. The Hall sensor detects a magnetic field due to the current through the cable, right? Are you sure there is still a current path through the load, i.e. cable?
     
  9. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    I checked it. When i used the same power source, it detected the frequency, on removing the two wires and connecting to the battery. No signal detected. Seems fishy.
     
  10. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    So your transmitter circuit didn't change, right. The "load" represents the cable to be verified. The Hall sensor is brought near this cable anywhere along the length of the cable .

    Does it work if you just connect the 2 commons of the different power sources together?
     
    Last edited: Mar 23, 2015
  11. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    I tried connecting both the grounds and the signal was still not present.
     
  12. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Sounds like your circuit is not detecting magnetic fields at all? This signal that you see maybe just coupling through the power supply via voltage drops?
    I am totally guessing here - post a schematic of the entire system so we can understand what you are doing.
     
  13. DickCappels

    Moderator

    Aug 21, 2008
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    It might be picking up the electric field in the wire and maybe without a common return the detected field is not as strong as when there was a return path.

    May we see your receiver schematic?

    How many amps are you passing through the wire?
     
  14. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    I believe that may be the case. I am passing about 2 amps on the wire. Innitially, i was getting the signal so i only used and non inverting amplifier along with LC filters to increase its amplitude and now that i am not even sensing the signal i do not know if it would work anymore.
     
  15. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    my initial proposal was to use an antenna to obtain the signal, however i was not able to capture much of the signal from same transmitter circuit. I am not really sure if i use a step up transformer in the transmitter and step the voltage to about 100V would make the antenna more receptive . Do you think the antenna might detect the electric field around it? I am only interested in detecting the frequency and following that path.
     
  16. DickCappels

    Moderator

    Aug 21, 2008
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    Electric fields? Soil conductivity might be a significant problem.

    Have you calculated the output of your hall device? I come up with .004 Gauss (2 amps @ 1 meter). With the Hall-effect device's sensitivity of 2.4 mv/G and the CA3140's gain of X 24 the microcontroller would only see 230 microvolts. Does that sound about right?

    Online calculator with which I calculated the flux density:
    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c2

    Have you looked at any commercial buried cable location systems?

    You might do much better to make a search loop that is resonant at 1 kHz or use a fluxgate magnetometer to detect a weak magnetic signal.
     
  17. Jayvin

    Thread Starter Member

    Mar 8, 2015
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    Actually i am not even getting an output out from the circuit. How do i make a search loop? Is it like the AM antennae?
     
  18. DickCappels

    Moderator

    Aug 21, 2008
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