Diode feedback.

Discussion in 'General Electronics Chat' started by geoffers, Jul 5, 2012.

  1. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Hi All,
    I was hoping someone maybe able to explain how the 'diode feedback' in a circuit I'm using works? I know it does but not how? Its a RFID reader working in the 125-134khz range using fdx-b protocal. I'm using appliction 2 on page12 of the data sheet(without the transistor, its all running at 5v) I tried to attach just the schematic but it wouldn't play the game! I would like to drive the coil at a higher voltage to increse read range using a H-bridge, looking at the circuit it appears that the 68k resitor and the 43k resistor form a potential divider? (pin rf is 1k to ground according the data sheet) If I've worked it out right, that means the first two diodes have 1.76v (running the circuit at 5v) above ground across them? As coil1 and coil2 alternate between gnd and 5v, how do the diodes increase the range? If I use my H-bridge to drive the coil (taking its input from coil1 and coil2) should the diodes have a seperate pdiv to put the same proportion of the voltage across the h-bridge at the head and tail of the first two diodes?
    Thanks Geoff
     
  2. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Hi Again,
    I was wondering if I've asked the question in the wrong way? If anyone could point me in the right direction to find out more myself it would be handy. A quick search for diode feedback doesnt throw up to much.
    Perhaps no-one else is to sure whats going on?
    Thanks Geoff
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,748
    4,796
    Patience.

    It's not unusual for a new thread to stew for a few days without getting a response; my first post went three weeks before getting the first response.

    This question might be better asked in the Communications forum, but since it is here, let it sit a while before you go asking the same question elsewhere (which is frowned upon).

    Part of the problem is that, unlike most questions asked here, you are asking something that looks like it would require some amount of reading just to understand what it is that is being asked. That's quite a bit of time invested for folks that are providing info for free. There are a number of folks here that are more than willing to do so, just for their own education or entertainment, but it has to fit in with their schedule.
     
  4. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Sorry, your right. Most of my other questions have been answerd very quickly! I saw my post disapering into the second page and thought no-one would see it! This forum has been a great help to me.
    Thanks Geoff
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Not just reading, but also opening of a PDF file, many people don't like opening user PDFs as PDFs can themselves automatically open web files and be a possible risk of virus or trojan infection etc.

    I apologise too for being off topic and not having an answer for your diode question.
     
  6. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    I didn't realise that! :eek: I can quite see why somone wouldn't want to open a pdf in that case. To upload a image does it have to already be on a web page? When I click that option I get Image URL? I would have just posted a schematic of the circuit otherwise.
    Thanks Geoff
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,748
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    Just attach the image file the same way you did the PDF.
     
  8. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Hi all,
    After a bit of farting around there should be a jpeg of the scematic for the circuit I'm using?
    Thanks Geoff
     
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