NFC Business Card [V2]

I did this project to see whether or not I would be able to effectively use SMD components to incorporate an MCU onto a small footprint whilst maintaining aesthetics.

ATMega328 PINOUT

The ATMega328 was chosen for this project as it's a low power chip that I am quite well versed in. The project did not require a lot of processing power and thus this MCU would suffice to flash a few LEDs and maybe a few extra additions in the future.

VCC: Digital voltage supply

AVCC: Analog voltage supply for the ADC. (Should be connected to the VCC pins, regardless of whether or not the ADC is active)

GND: Ground

PB | PD | PC: These are bidirectional I/O pins with internal pull-up resistors. B and D are 8-bit whilst C is 7-bit. Additionally, some of the pins serve other purposes and may need to be designated as an I/O pin in the IDE.

• PC6: It is by default used as the RESET pin and should not be used for I/O purposes. A low level on this pin will initiate a reset.
• PD1(TX): Primarily used as the transmission line for UART/USART communication. Connect RX line of other component if being used for this purpose.
• PD0(RX): Primarily used as the receive line for UART/USART communication. Connect TX line of other component if being used for this purpose.
• PB3(MOSI)/PB4(MISO): By default an I/O line, but can be used as an SPI transmission/receive data transmission line. Usually used for burning the bootloader onto the chip.
• PB5(SCK): By default an I/O line, but can be used as the clock line for SPI. Usually used for burning the bootloader onto the chip.

AREF: Analog reference pin for the ADC. [Capacitor is acting as a decoupling capacitor to reduce noise.]

ADC6/7: Serves as the analog inputs to the ADC. These pins are powered from the analog supply (AVCC) and serve as 10-bit ADC channels.

NT3H1101/NT3H1201 (NFC Chip) PINOUT

This chip is what powers the NFC aspects of the business card. NFC (Near-field communication).

1. LA: Antenna connection LA.

2. VSS: Ground.

3. SCL: Serial clock for I2C communication.

4.FD: Field detection.

5. SDA: Serial data communication line for I2C.

6. VCC: External power supply.

7. VOUT: Output voltage. Voltage is sourced from the NFC device which taps with the NFC reader.

8. LB: Antenna connection LB.

ANTENNA

This square antenna design was sufficient for our purposes and works well.

DO NOT PLACE ANY GND COVERING ON OR BELOW THE ANTENNA

MOLEX C134092 (USB-C) PINOUT

USB-C was chosen for the card as it was an easy way to power the chip with a stable 5V voltage source. No external voltage regulation was required.

GND (A1, A12, B1, B12):Ground connections.

VBUS (A4, A9, B4, B9):Power supply pins (Up to 5V by default, but can be higher with Power Delivery).

D+/D- (A6, A7, B6, B7):Differential data lines used for USB 2.0 data transfer.

TX+/TX-(A2, A3, B10, B11): High-speed differential pairs used for USB 3.1 data transmission.

RX+/RX- (A10, A11, B2, B3): High-speed differential pairs used for receiving 3.1 data.

CC1/CC2 (A5, B5):Configuration Channel pins used to determine the orientation of the connector and to negotiate power levels. In one orientation the CC1 on the host will be connected to the CC pin on the plug, and CC2 will be connected and vice versa

SBU1/SBU2 (A8, B8): Sideband use pins that can be used for alternate modes such as audio or video so as not to interfere with standard USB data lines. These pins for example in DisplayPort Alt mode can be repurposed to carry auxiliary DisplayPort signals.

SHIELD (S1, S2, S3, S4): Protection pins. Connect to GND, although there are a few differences with our setup.

TERMINOLOGY:

Differential Data Line:A transmission line that carries digital or analog signals as a voltage difference between two conductors is typically referred to as a differential pair. This configuration enhances noise immunity by cancelling out common-mode interference, which affects both conductors equally, and reduces the impact of ground offsets. Electrically, these signals are equal in voltage but inverses of each other.

When these two signals are processed by the receiver, they are subtracted from each other, as the receiver acts as a summing amplifier, leading to two possible outcomes. If the first voltage (V1) and the second voltage (V2) are not inverses of each other, they cancel out, resulting in a signal of 0. However, if V1 and V2 are inverses, the output voltage is twice the magnitude of the original signals: V2 - (-V1) = V2 + V1. The common-mode inference in each line will not be inverted, so it is removed.

PCB:

Final PCB assembly. V2 and V1 (Top and bottom respectively)