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Topic: RFID - RC522 voltage problem/solution (Read 376 times) previous topic - next topic

gordonw

Attached this module to an UNO or Leonardo SPI interface and measured the voltages on the pins.

For some reason, the 3.3V line to the module had been raised to about 4v by this module.

I removed the 3.3v input connection AND THE MODULE STILL WORKED. It appears that the 5V SDA (chip select) and/or the reset pin from the arduino provides all the voltage needed to get this module working and the 3.3v input is not actually required. This over-voltage on the 3.3V line was affecting other devices on my SPI bus which also need 3.3V. Bad design but it is a very cheap module. In fact removing the 3.3V from the device means that the red light on the device only comes on when the device is polled rather than being on continuously. Thought others might benefit by knowing this.

Not sure what affect a voltage >3.3v going back into my arduino 3.3v pin would have :-( is that 3.3V supply line diode protected in some way ?

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