AD7689 Circuit

Hello,

I'm trying to interface and AD7689 to a Raspberry Pi but for some reason, I am not succeeding. I have fried a Raspberry Pi in the process so I'd like to make sure that the circuit I am using is ok. The smoke came out near the power port of the raspberry pi. If anyone could have a look at the attached image and let me know if they can spot any reason why it would break the Raspberry Pi I would be very much thankful.

Thanks



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[edited by: @skowalik at 5:10 PM (GMT 0) on 6 Feb 2020]
  • 0
    •  Analog Employees 
    •  Super User 
    on Feb 6, 2020 5:08 PM

    Tomas,

    Can you please comment on what the A1931 is as this may help us understand the fault mode a bit better.  From a first glance there isn't much that is fundamentally wrong with the AD7689 circuit connection but I would recommend you do the following.

    1) Short IN1-IN7 to a known potential, maybe ground just to ensure the inputs are in a known state.

    2) Add a 10uF decoupling capacitor from REF to GND. 

    Note:  I assume you intend to use the internal reference and buffer and that you've enabled it through software.  

    3) If you can I would put some sort of control on the sleep pin of the AD1931. In fact are you sure that that device isn't always powered off?  

    I would also recommend looking at what device failed on the RASPPI.  My guess is something got hot because of some short circuit current and from there we can work back to a hypothesis of what might be wrong.

    Regards

    Sean

  • Hi Sean,

    Thank you for your answer. 

    The A1931 is a Hall Effect sensor (datasheet: https://documentcloud.adobe.com/link/track?uri=urn%3Aaaid%3Ascds%3AUS%3A0094365f-923c-4fbc-abc3-73e88ab153fe )

    I will do the first two points you mentioned. About the third one I will put some control on the sleep pin of the AD1931, but at the time I was just hoping to read some data from it.

    Also, do you know how I could look at what device failed on the RASPI? I've been trying to figure it out but I haven't managed a way of doing it.

    Thanks

  • Thanks for your answer, Sean

    The A1931 is an analogue Hall effect sensor from Alegro. I will address your two first points. About the third one, I can and will at some point add some control to the sleep pin of the sensor, but at the time I'm just trying to read some data from it.

    Also, do you have a suggestion on how to look at what device failed on the RASPI? I have been trying to figure it out but I haven't managed to find a way of doing it.

    Thanks

    Regards

  • 0
    •  Analog Employees 
    •  Super User 
    on Feb 7, 2020 4:22 PM in reply to tomasveiga

    Tomas,

    I made an assumption that your using the Raspberry Pi 3 and that you're using the GPIO expansion port 3.3V rail.  Looking at the schematic it's likely something in the regulator that is generating the supply rail which is U3.  I would start there.  

    Sean