Increasing RFID range.

Discussion in 'Wireless & RF Design' started by geoffers, Jun 9, 2013.

  1. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    Hi all,

    I've been thinking recently about trying to increase the range of my RFID reader system, I'm stuck with the lf type of RFID 127~134 kHz used for id in livestock. I've a reliably working system using the Atmel U2270b front end chip.

    Range of these tags is quite short and as far as I can see there are two ways to increase range, a bigger reader coil or pushing more current through a given size coil?

    I've got pretty much as big a coil as practical for my hand held reader so am now thinking of ways to get more current through. I think I'm going to have to use a MOSFET H-bridge and drive it with the PWM module on my pic as I think I've reached the limit of supply on the Atmel.

    This is where I could do with some help, the reader at the moment uses a 9v battery and also has to detect a HDX transponder (which means the field is turned off to wait for the HDX to respond).

    Is it practical to use a step up boost converter to charge a capacitor to a higher voltage, say 30v while the field is off then use the 30v to supply the H-Bridge and hence drive the coil at a higher current? All be it briefly!

    I've been doing a bit of reading up and read that a capacitor used for storage is about 50% efficent? Is this correct? Anyone have any idea what sort of losses I might experience with the boost converter etc? I've a funny feeling they might be quite high.

    Thanks Geoff
  2. LDC3

    Active Member

    Apr 27, 2013
    Since you can't create power from nothing, the output from your boost circuit cannot be more than what you start with.
    9 V x 100 mA = 36 V x 25 mA.
    Then when you discharge your capacitor, how much current are you going to utilize? 100 mA, 500 mA or even 1000 mA? That would mean your minimum charging time would be 4, 20, or 40 times the discharge time. How often do you need to send a pulse? Is your receiver capable of separating multiple RFID transmissions?
    I think your project got a lot more complicated.
  3. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    Thanks for the reply, I've been doing a bit more reading up, (I should have done before I posted, sorry!) If I've understood things right and require 1000mA for say 50mS it would take 2s to recharge? As tags are read one at a time multiple reads shouldn't occur.

    Some sums if I've got them right say I need roughly 330uF to give me that sort of current for 50ms at 36v.

    This all seems reasonable at the moment, the atmel can deliver 200mA at 7 volts so a capacitor would certainly get more power through the coil.

    My other option is more batteries in series which does seem simpler! Although it would add weight and cost?

    Sorry if my questions seem basic I've no formal teaching!

    Cheers Geoff