TRF7970A: Multiplexing the DLP-RFID2 external antenna output

Hello Ken,

Have you read through our Antenna Multiplexing guide? That would provide you more technical background on antenna muxing: www.ti.com/.../sloa231

Regarding the application issue you have, if you use the RF430FRL152H with just a normal reader setup where you aren't muxing antennas, does it work exactly as you want? It almost sounds to me like the RF430FRL152H is only coded to communicate with the sensor when it is powered on.

I can't comment if the DLP is freezing up as while it uses the TRF7970A, I am not experienced with it to comment how it would act in the application you are doing (though I believe DLP did some sort of mux setup which should work...)

Hello Ralph,

I read SLOA231. It pointed me to SLOA167, TRF7960A RFID Multiplexer Example System, which is much closer to my project.

In SLOA167 Section 4 System Host Commands, there are references to turning off/on the RF Transmitter. Studying that section to see if I need to incorporate those commands into my project.

When I disable muxing and "stare" at a single antenna, the project works exactly as desired.

We're using a Peregrine PE42440 mux. The DLP external antenna (pin 13) is connected to mux RFC (pin 11). I'm controlling V1 and V2 to select between 4 external antennae.

Do you see any fundamental problems with how we're attempting to mux the DLP external antenna output?

Thank you,
Ken

Hello Ken,

You may need to monitor with an o-scope if the antennas from the DLP are emitting an RF field continuously after switching to it. You can do this by making a loop with the scope probe and the ground clip, and then hover that loop over the antenna. You can see the RF field this way.

If the field is turning off too soon, then you know the issue is on the DLP side, but if the field holds continuously for each antenna that is switched to it, then something is amiss on the RF430 boards.

Hello Ralph,

With our TI RF Spectrum Analyzer, measured -45 dBm at the Pulse/Larsen W3579 when the antenna is selected by the mux, -75 dBm when not selected.

It would be great if TI could provide some hints or suggestions concerning what actions I need to take for muxing to work, or what steps for me to research along the path of making muxing work.

Thank you for your help!

Regards,

Ken

Hi Ken,

I have no experience with Muxing unfortunately, but I know someone who does although he is out of office until next week. I'll see if I can loop him in when he returns.

Hi Ralph,

OK, I'll keep exploring muxing on my end, until we could get some muxing feedback next week, early in the week I hope.

Thank you for your help.

Ken

Josh,

SLOA167 is the most complete write up I've encountered, very helpful.

Here's my attempt at something similar to your Figure 6:

Start Init
0108000304FF0000 // ping the dlp
010A0003041001210000 // from 7970A GUI app Set Protocol cmd
010C00030410002101020000 // ditto
0109000304F0000000 // agc toggle from 7970A Inventory cmd
0109000304F1FF0000 // am pm toggle from same
01080003042B0000 // enable external antenna
010A0003041000010000 // turn off RF, from SLOA167
End Init

Main Loop
Select antenna 1 via PE42440 mux
delay 1 mSec
010A0003041000210000 // turn on RF, from SLOA167
delay 1 mSec
01130003041802210001007000010100000000 // initiate sampling

// my smart tag code initiates i2c comm with LIS3 magnetometer

010B000304180220000000 // check status for sampling complete
010B000304180220090000 // get magnetometer results
delay 1 mSec
010A0003041000010000 // turn off RF, from SLOA167
delay 1 mSec

Select antenna 2 via PE42440 mux
same sequence as for antenna 1

repeat for antenna 3 then 4
end Main Loop

Please advise if I've misunderstood the commands and/or sequences.

Thank you for looking at my post.

Ken