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32400B Xbee-USB-Adapter - Vdd pad as +5V output — Parallax Forums

32400B Xbee-USB-Adapter - Vdd pad as +5V output

circlemecircleme Posts: 4
edited 2014-08-28 23:54 in Accessories
Great little board, my XBee 900HPs are happy. I am powering them with battery packs that supply over USB cables (+5V only). Now I need to operate a relay that needs +5V on its coil. I was hoping to pull +5V off the Vdd pad of the adapter. This doesn't seem to have +5V on it however, but about +1V.
The schematic shows the Vdd pad directly connected to the +5V IN of the FAN chip, so I'm confused why I see only +1V.

Thanks.

Comments

  • PublisonPublison Posts: 12,366
    edited 2014-08-26 08:27
    circleme wrote: »
    Great little board, my XBee 900HPs are happy. I am powering them with battery packs that supply over USB cables (+5V only). Now I need to operate a relay that needs +5V on its coil. I was hoping to pull +5V off the Vdd pad of the adapter. This doesn't seem to have +5V on it however, but about +1V.
    The schematic shows the Vdd pad directly connected to the +5V IN of the FAN chip, so I'm confused why I see only +1V.

    Thanks.

    Welcome to the forums!

    Looks likes you should get a +5 volt off of the VIN or VDD. What measurement device are you using? When using a DVM I forget to switch between AC and DC measurement.

    If you do get it sorted out, don't forget to put a diode across the relay. I hope the relay doesn't more current than the battery can handle. A link to the relay in use would be helpfull.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-08-26 08:34
    Hello,

    In the schematic there are also diodes designed to prevent voltage from one source or the other from bleeding across. Basically voltage at Vdd cannot be seen at Vusb and voltage at Vusb cannot be seen at Vdd. Since the Vdd is an input terminal you would only be able to get voltage from it if the voltage was being fed into that pin.
  • PublisonPublison Posts: 12,366
    edited 2014-08-26 09:00
    Chris,

    Confused.
    Are we looking at the same schematic?

    http://www.parallax.com/sites/default/files/downloads/32400-XBee-USB-Adapter-Documentation-v1.0.pdf

    I do not see diodes except for LED's

    I'm not sure what the OP means by 3400B.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-08-26 09:28
    Perhaps not. That documentation has the Rev A schematic, however the OP specified Rev B in his message, at least that's how I took 32400B <--. I looked at the Rev B schematic from the product page.

    Tip: Always check your board revision against the docs/schematic. =)
  • PublisonPublison Posts: 12,366
    edited 2014-08-26 10:37
    Chris Savage wrote: »
    Perhaps not. That documentation has the Rev A schematic, however the OP specified Rev B in his message, at least that's how I took 32400B <--. I looked at the Rev B schematic from the product page.

    Tip: Always check your board revision against the docs/schematic. =)

    Duly noted. That's why people should like to the particular board. I didn't notice the Rev B.

    You guys are always ahead of me. :)
  • circlemecircleme Posts: 4
    edited 2014-08-26 22:01
    Publison wrote: »
    Duly noted. That's why people should like to the particular board. I didn't notice the Rev B.

    You guys are always ahead of me. :)

    Most definitely you both are ahead of me by miles! I also was using the rev A schematic. The diode explains it.
    I will use a different +5V source for the relay. Problem solved. Thank you.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-08-27 08:19
    The other option is to connect you existing 5V supply to the Vdd pin rather than using the USB jack. In saying this of course I have to ask, how are you communicating with the 900HP module using 32400? Typically this would be done via the host PC. Since the DIN/DOUT lines are connected to the FTDI USB chip they would not be available to an external microcontroller (at least not DIN).
  • circlemecircleme Posts: 4
    edited 2014-08-28 00:40
    Hi Chris, I appreciate that you have to ask. These are remote boards, no PC. In normal operation, the USB port is solely a convenience to connect +5V via an external phone cell battery. Only the hub radio needs a PC in my particular application. Here's a video on what I'm implementing, https://www.kickstarter.com/projects/107313729/distance-music-at-lake-eola-project?ref=nav_search.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-08-28 09:07
    Interesting project, however my concern was that if you're talking to the XBee module from a microcontroller there would most likely be contention between the DIN/DOUT lines connected to the microcontroller and the ones connected to the FTDI chip on board. The XBee USB Adapter was intended to connect an XBee module to a PC only for either configuration or communication. The lines were all brought out for testing or so you could still access the analog pins or use pin passing, etc. I guess I am curious what you have connected to the adapter and how.
  • circlemecircleme Posts: 4
    edited 2014-08-28 23:54
    Hi Chris,
    Most of my XBEEs are standalone. I configure them with via USB and a laptop, but once configured they need not be connected again. Only the hub needs the serial USB connection.
    The XBEE remotes use a Digital out to a relay, and maybe a couple of analog inputs to report on batteries. Very simple (a 3.3 to 5V level shift was the only challenge). Not much interesting going on, really, but I'm very glad it is so straightforward. I can concentrate on the application on the laptop. If I have questions I'll be sure to ask you. Thanks for being so supportive to this technology. I plan on using it in the future for interesting sensors, and IoT in general.
    k
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