Question about NFC

Dear All,

I have a project which is using PN532 Seeedstudio NFC Shield. And i have several questions to ask:
1.
I am going to connect it with a device which also transmits an RF as much as 868.3MHz.
So i am wondering if this RF will interference the radio frequency from the NFC shield?
Or the NFC shield has already an EMC filter that can reject all surrounding noises?
If there is any possible interference, how can i prevent the noises interfering the RF of NFC?
I have been thinking about making low pass filter of 14Mhz or bandpass filter of 12-14Mhz.

I am going to attach the device through I2C connection. But the device which i am going to attach outputing as much 7-12V,
While the NFC has 5V. Will the voltage be tolerated or this situation requires logic level converter?

Let me know what is your suggestion to this…

Thank you in advance.

Best Regards,

Stella

If there is any possible interference, how can i prevent the noises interfering the RF of NFC?

Yes there is a possibility of interference but it is small because the frequencies are far apart. The effect will be to make any receiver less sensitive that it otherwise would be. The solution is to put a notch filter on the input of one device that is tuned to the frequency of the other.

Will the voltage be tolerated or this situation requires logic level converter?

You require some sort of logic level conversion, often a pair of resistors will do.

Hey, Mike!
Thanks for the respond!

You require some sort of logic level conversion, often a pair of resistors will do.

I have been thinking about using TXB0108, since, it converts from any voltage to any voltage. However, it doesn’t work well for i2c (due to its strong pullups that confuse the auto-direction sensor). Meanwhile, BSS138, converts from 3.3V to 5 V and vice versa (I wanted to convert from 7V to 5V).
Is there any suggestion of logic level converter that suitable for my case?

Thank you in advance.

Best Regards,

Stella

But the device which i am going to attach outputing as much 7-12V,

Are you sure of that?

An I2C interface should not output any voltage, it should only pull down to ground. Having an I2C buss pulled up to 12V would be unique as far as I know.

However a simple pair of transistors will do like this:-

AN10441.pdf (52.4 KB)

Are you sure of that?

I was even surprised too with the device specification that i read. see it on the picture i’ve attached. Sorry i cannot attached all of the document, it is confidential document. So, i was pretty sure about it, unless if i misunderstood it. Or i can ask the writer to confirm this. (i hope this is a mistake, so i don’t have much effort on converting sigh)

However a simple pair of transistors will do like this:-

Thank you, captain! This is helpful! :slight_smile:

pin.png

So, i was pretty sure about it, unless if i misunderstood it.

Well if I was reading that I would not assume that it meant the I2C signals were at 12V. To me this reads as an unregulated input voltage, and the board has a built in regulator to take it down to 5V or 3V3 and the I2C bus is not internally pulled up. There are very few ( well I don't know of any actually ) digital ICs that take anything over 5V so it is highly unlikely they are going to signal at 5V.

However as a test, power it up and measure the voltage on the two signal lines. When there is no traffic these lines sit high so if you measure them with the device just powered up and there is an internal pull up you might see a voltage. However, my guess is that you will not measure any voltage on these lines just on power up.

Ignoring the CD4000 series then :) I suppose that's understandable by now.

MarkT: Ignoring the CD4000 series then :) I suppose that's understandable by now.

Yes, never did use them at anything other than 5V and never saw an I2C interface on any of them. :P

Ignoring the CD4000 series then smiley I suppose that's understandable by now.

Sounds like it is not actually 7V-12V. Well, I'll check it by multimeter just to ensure it. :)

Anyway, I need to come back to the question about the interference

Yes there is a possibility of interference but it is small because the frequencies are far apart. The effect will be to make any receiver less sensitive that it otherwise would be. The solution is to put a notch filter on the input of one device that is tuned to the frequency of the other.

I have been thinking to use a longer cable, so it gives distance between both transmitting RF devices. Can it be effective too to prevent interference?

Can it be effective too to prevent interference?

Yes to some extent increasing the distance between a transmitter and receiver will reduce the decrease in receiver sensitivity but the only way to know if you have trouble is to try it. This is because the manufacturers of both transceivers will not have characterized the response so far out of band.