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Overview The project uses an Atmel ATtiny85 AVR microcontroller and a coil to build an RFID tag. Explanation The AVR is being powered by the coil through two of its I/O pins. The voltages on the pin are prevented from rising above the chip’s supply voltage by the clamping diodes on the I/O pins since they are useful for capturing static discharge. The chip has no power and the supply voltage is zero when the RFID tag is first held up to a reader. The two I/O pins are presented with a sine wave with amplitude of a few volts when the coil starts to pick up power from the RFID reader. Some energy is diverted from the coil to the chip’s supply rails through the clamping diode when the sine wave exceeds the supply voltage. This results to truncating the coil’s sine wave as the chip is powered. The sine wave will look a lot more like a square wave by chopping off the top and bottom of the sine. Specified for operation at voltages as low as 2.5V is this particular ATtiny45 chip. The AVR’s die capacitance is used for power filtering purposes. Rest of the project
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