MDFLY V-level translator

Discussion in 'The Projects Forum' started by Andreas, Jan 9, 2015.

  1. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    Hi,

    I recently purchased a 2-ch MDFLY voltage level translator which is a device that can up-shift or down-shift voltages depending how one configures it (see attached spec sheet).

    Please could someone tell me why I get voltages on both transmit and receive pins with nothing connected. That is, I get 3.3V on the TXA and RXA pins and 5V on the RXB and TXB pins.

    So when I feed in a 100Hz, 5V square wave on BNC-A (TXA) I see a very jaggedy 1.7Vpp square wave on BNC-B (RXB) and not a nice clean 3.3Vpp square wave as I was expecting. Why?

    Am I missing something fundamental here in concept?

    P.S. Another pic is attached showing the complete cct incl a 3.3V / 5V PSU. Not sure whether it will extract as I had to compress it as for some reason AAC would not accept a JPG. Only a PNG which my camera does not do. And please don't tell me to convert it to a PNG, 'cause I already tried that (on max compression) and the file size grew from 1.6MB to 8.5MB

    ;-)
    Tnx
     
    Last edited: Jan 9, 2015
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I post JPGs here all the time. There is a max size limit which you are exceeding. Your camera should be setable to smaller (fewer pixels) image. I will not open a .Zip.

    MDFLY needs to learn how to spec its products. I can see why you are confused.

    Can you read the chip part number off the actual pcb? If we knew what chip that was, we could figure out how to connect it up by looking at the data sheet for the chip(s).
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello Mike,

    I unpacked and resized the image.

    [​IMG]

    Bertus
     
    Andreas likes this.
  4. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    Thanks mate.
    Andreas
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    I have taken a part of your picture to show the SMD markings:

    [​IMG]

    Unfortunately, I could not find any info using the codes.

    Did you power the module correctly?
    5 volts on the one side and 3.3 volts on the other side?
    Are you loading the 3.3 Volts side to much, as you say you have a to low output?

    Bertus
     
  6. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    Firstly thanks for taking interrest in my post Mike and yes, taking a lower res photo was on my mind but Bertus has come to the rescue.
    On the two 6-pin SOT-23 packages is printed CT1F which compares favourably with the SN74LVC1T45 that the clever chaps at TI produce.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    After seeing the partial data sheet, the only thing that comes to mind is to ask: is the neg. side of the 3.3V supply tied to the neg. side of the 5V supply?
     
  8. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    Hi Mike,
    The supply lines are all connected to 0V from the PP3 9V battery which powers the PSU. I should say at this point that my jagged (noisy) output signal is now showing a clean 3.3V square wave after I swapped my (dodgy) BNC lead with a quality CRO lead. Though it still doesn't answer my initial question as to why I get voltages on TXA, RXA, TXB and RXB with nothing connected. I guess these pins float high unless forced to ground by the incoming pulse...
     
    Last edited: Jan 10, 2015
  9. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    MDFly Logic Level Converter 2 Channel, 2.5V/3.3V/5V (Man SKU CV0035).

    I do not understand why I get 3.3V on the TXA and RXA pins and 5V on the RXB and TXB pins with NOTHING CONNECTED to them...?

    I would have thought these should be either High impedance or 0V. If they are sitting at a logic high, won't this affect the incomong signals?

    Please can anyone explain this.

    P.S. I've attached the full data sheet from TI which has the relevant chip info.
    Thanks
     
  10. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    Pull up resistors that's why!
    Looks like I'm answering my own questions here.
    I think we can put this one to bed now.
    Thanks for all previous replies.
    ;-)
     
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