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I'm looking to follow up on a question (asked by another) that wasn't answered to my satisfaction in another question. RFID Antenna Array

I am successfully using the ID Innovations ID-2 chip to read 125kHz RFID tags. Furthermore, I have sucessfully tested connecting antennas with RG-58 coaxial cables with SMA connectors up to 8' in length. I now need to use need to use multiple antennas to scan in different locations using the same ID-2 reader IC.

I hesitate to use traditional analog multiplexers because the signal sent from reader to antenna is extremely analog, and ranges from a few mV to over 100V and I'm worried that the properties of MUX ICs will destroy the signal to/from the antenna.

I basically need a "2-pole,4-throw selector switch" that i can control with some I/O pins from an Arduino or other microcontroller.

Can anyone point me in the right direction? someone suggested using mosfets in comments on the other question? Thanks in advance!

I will make whatever board i develop to do this available as open source hardware.

ID-2 Datasheet

Update: I would use something like an analog switch IC if it didnt seem like the signal would exceed the maximum voltage of the IC. Am I wrong?

Update2: Found some Solid State Relays that look like they might be the best of both worlds. Im going to go ahead with these for now. http://www.mouser.com/catalog/catalogusd/646/1981.pdf

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anarnold
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  • 100V seems suprisingly high? That IC claims to be good up to 15MHz; I would try it in a test rig and see. It will effectively be a set of neatly packaged MOSFETS. – pjc50 Jun 12 '13 at 21:21
  • I will experiment running a single antenna channel through mosfets and report back. – anarnold Jun 12 '13 at 22:32
  • @anarnold, any progress? I am also interested in this! – lucidgold Jun 04 '14 at 19:59
  • Yep, an array of the relays mentioned in Update2 worked just fine without noticeable reduction of antenna signal. – anarnold Jul 08 '14 at 00:28
  • Anarnold, please can you post more details about your solution using solid state relays? I want to do something similar using a 134kHz system (Priority1 RFIDRW-E-TTL) and a Raspberry Pi. Thanks -- Lawrence – Lawrence Moon Jul 03 '16 at 21:02
  • See this Texas Instruments TRF7960A RFID Multiplexer: http://www.ti.com/lit/an/sloa167/sloa167.pdf – smorgan Apr 14 '17 at 03:49
  • @anarnold did you ever post this as open hardware somewhere? – DannyThunder Nov 13 '18 at 10:25

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No, that analogue switch won't do given your signal requirements. Because of the need to keep integrity as high as possible I'd use relays. You'll need a relay that is 5V logic driven and has decent contacts. You'll need to switch both legs of the circuits unless of course you can make a decent claim for one of the legs being a solid 0V.

For the relay type I'd strongly consider using a sealed reed relay.

I'd use this type here. It's features are

  • standard footprint
  • single pole single throw (two needed per antenna)
  • 200V contact
  • 500mA switching
  • 500 ohms coil (10mA to drive direct from logic)

There are two pole versions but unless space was a big issue I'd work with these. You'll need two per antenna meaning a drive capability of 20mA from your logic. This should not be a big issue.

Remember, if you use transistors to drive the relay coil, add an anti-parallel diode across the coil.

user2943160
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Andy aka
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  • Thanks so much for the clear and concise answer I was looking for. I think i will build the board with these as a reference, then try an approach with mosfets and perhaps the analog switch ic, and compare their performance to the relays. As soon as I have the minimum rep, I will upvote it. =) – anarnold Jun 12 '13 at 22:30