Connecting a Sensor to an RFID Chip: A Mechanical Engineer's Guide

[volican]

Hi,

I have an internet of things project and I am wondering how you would cheaply go about connecting a sensor to an RFD chip? I am a mechanical engineer by training so this is a bit of a learning curve, apologies if it is a really basic and obvious question. I have found this chip:

http://uk.farnell.com/nxp/sl3s4011f...2?MER=bn_level5_5NP_EngagementRecSingleItem_3

It makes reference to something called I2C. A quick googling give me the gist that it is for I/O.

Basically what I am trying to achieve is this:

1. The reader transmits a signal
2. The RFID chip receives this signal to provide power (this project requires a passive tag)
3. The sensor value at that point in time (which will actually just be the voltage value of a variable resistor) is logged
4. The ID of the RFID chip and data value that was just saved is sent back to the reader

Have I understood correctly that this I2C pin will allow me to do this? From what I read in the technical documentation I think so. If so would I have to build extra circuitry or could I connect it straight up? I want to use power that is transmitted from the reader. If I am totally wrong would you be able to point me in the right direction. Much appreciated for your help :)

 

[berkeman]

Hi,

I have an internet of things project and I am wondering how you would cheaply go about connecting a sensor to an RFD chip? I am a mechanical engineer by training so this is a bit of a learning curve, apologies if it is a really basic and obvious question. I have found this chip:

http://uk.farnell.com/nxp/sl3s4011f...2?MER=bn_level5_5NP_EngagementRecSingleItem_3

It makes reference to something called I2C. A quick googling give me the gist that it is for I/O.

Basically what I am trying to achieve is this:

1. The reader transmits a signal
2. The RFID chip receives this signal to provide power (this project requires a passive tag)
3. The sensor value at that point in time (which will actually just be the voltage value of a variable resistor) is logged
4. The ID of the RFID chip and data value that was just saved is sent back to the reader

Have I understood correctly that this I2C pin will allow me to do this? From what I read in the technical documentation I think so. If so would I have to build extra circuitry or could I connect it straight up? I want to use power that is transmitted from the reader. If I am totally wrong would you be able to point me in the right direction. Much appreciated for your help :)

Can you Upload a schematic of your uC I2C connections, and a drawing of the overall system please? It's not clear if the I2C connection is in your head-end Master system device, or you slave passive RFID device to the sensor. At least it's not clear to me yet.

 

[jim hardy]

Have I understood correctly that this I2C pin will allow me to do this? From what I read in the technical documentation I think so. If so would I have to build extra circuitry or could I connect it straight up? I want to use power that is transmitted from the reader. If I am totally wrong would you be able to point me in the right direction. Much appreciated for your help :)

No takers yet ?

I wouldn't have believed it before looking at that datasheet , but it looks to me like you're right - it just might work...

The UCODE based label/ tag requires no external power supply for contactless operation.
Its contactless interface generates the power supply via the antenna circuit by propagative energy transmission from the interrogator (reader), while the system clock is generated by an on-chip oscillator. Data transmitted from the interrogator to the label/tag is demodulated by the interface, and it also modulates the interrogator's electromagnetic field for data transmission from the label/tag to the interrogator.
A label/tag can be then operated without the need for line of sight or battery, as long as it is connected to a dedicated antenna for the targeted frequency range. When the label/tag is within the interrogator's operating range, the high-speed wireless interface allows data transmission in both directions.

To read the value of that resistor will require an analog interface to digitize it.
and i don't know how you'll power that. If i read right you might get a few microamps from the VDD pin but I'm at a loss what they mean by "I²C on VDD pin". Seems unnatural to use same pin for power and communication.
Here's a snip from the datasheet http://www.farnell.com/datasheets/1996754.pdf section 13

Must be somebody here more current than i am on these things.
I've only used I²C once twenty years ago with a traditionally powered 5 volt microprocessor. Used a Maxim DAC to produce analog voltage from a digital value i handed it via I²C from my microprocessor.
You need to go the other way, digitize with an ADC then hand the value to RFID processor via I²C.

I never tinkered with RFID so can't help, sadly - looks like fun..
maybe this will prime the pump, though.Request a sample and try it out ?

old jim

LATE EDIT I'm out of my depth here
but food for thought...
micropower ADC
http://www.ti.com/lit/ds/symlink/ads7924.pdf

 

[volican]

Thanks very much for your reply. I decided to go down the route of using an ATtiny10. From what I have read if you connect it up to an inductor you can mimic an RFID tag. I will be experimenting to see if I could also connect up the sensor.

 

[jim hardy]

I'm continually amazed at what powerful devices you young folks have available, and how quickly you become adept at using them.old jim.