I2C communication - VCC over NFC antenna, the rest (SCA, SCL and GND) over wires

Using Arduino General Electronics
1

Hi there,
I'm working on a project involving NFC tags.

I am interested in providing VCC over NFC antenna and SCA, SCL and GND via wired connection.

Could this allow the I2C communication?

Thanks!

2

It depends on how you hook them up. If any of the I2C wires are over 25cm / 10" expect problems. There is also more then what you are stating post a simple schematic showing all of the connections and note any wire connects over 10" / 25cm.

3

What does that mean?

4

I think it means it wirelessly powered. NFC is not wireless power, its near field comms, but I can understand the confusion as they both use near-field magnetic induction.

5

We assume you mean a DC voltage that can power something connected to a terminal called VCC. Is that close? First all RF that an antenna uses is AC, and cannot be DC without rectification.
Second, the RF voltage at any antenna is measured in MICRO VOLTS. That is millionth of a volt. Power at that antenna is in MICRO WATTS. That is millionth of a watt. How much power does your VCC device need?

6

Hello,
so I'm using NTAG5 from NXP Semiconductors, specifically NTA5332 NTAG 5 boost - NFC Forum-compliant I2C bridge for tiny devices. The tag has energy harvesting which means it can harness the power over NFC antenna and provide up to 30 mW on Vout pin. I meant Vcc in terms of I2C, on Wikipedia its also mentioned as Vdd, the positive wire of I2C (SDA, SCL, +, -), there should be a pull-up resistor between Vdd and SDA and Vdd and SCL, but it should be only once on the I2C network, not on every device.

The tag also has a function command called STAY QUIET which I would send to the tag via I2C when the tag would be inserted in the holder where the contacts for I2C wires would connect. When the tag receives STAY QUIET command it becomes invisible on the NFC side, so it doesn't respond to NFC requests. Contrary the tag would leave the STAY QUIET mode when disconnected from the I2C wires and would again work as a NFC enabled tag.

(In the context of NFC (Near Field Communication), "stay quiet" refers to a specific state in which an NFC device remains silent or inactive to conserve power and avoid interfering with other NFC devices in the vicinity. When an NFC device is in the "stay quiet" state, it does not transmit or respond to NFC communication requests. - source ChatGPT)

So to refine my question: I am asking if i could connect SDA, SCL and GND via a connector and then use an NFC antenna which would automatically power the NTAG5 (also in STAY QUIET mode) and the I2C communication would be able to work in this way without physical Vdd connection?

I have added some schematics to the reply.

Schematics
Schematics1008×510 44.7 KB

Thanks!

7

The SDA and SCL are idle high. You can not make them low, because then the I2C bus does not work anymore. If a device on the I2C bus has no power, then the I2C bus stops working.

Since SDA and SCL have a pullup resistor, they might give power to chip, via the internal ESD protection diodes in the chip.

Can you tell what your project is for ?
If you have already three wires, why not add a fourth wire with VCC ?

Let's do some math:
Suppose the Master is a 5V Arduino board and there are 4k7 pullup resistors for SDA and SCL and the chip starts working at 2V, and the internal ESD diodes in the chip have a forward voltage drop of 0.5V.
(5-2.5)/4k7 = 0.5mA
Then SDA and SCL combined can give 1mA to the chip.

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