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By Dave Morales
#64166 Hello.

I'm using a Nodemcu v1.0 ESP-12E and a NFC Module V3 from Elechouse connected by I2C using pins D1 as SCL and D2 as SCL and power to 5v. Also, i have connected an LCD 16x2 by I2C too.

I'm using the following library:

https://github.com/elechouse/PN532

And running the I2C Scanner form the next URL:

http://playground.arduino.cc/Main/I2cScanner

When I run the I2C scanner whitout the PN532, I easily get the address of the LCD (0x27). But when I plug the PN532 I start to get the next output:

Code: Select allScanning...
Unknown error at address 0x01
Unknown error at address 0x02
Unknown error at address 0x03
Unknown error at address 0x04
Unknown error at address 0x05
Unknown error at address 0x06
Unknown error at address 0x07
Unknown error at address 0x08
Unknown error at address 0x09
Unknown error at address 0x0A
Unknown error at address 0x0B
Unknown error at address 0x0C
Unknown error at address 0x0D
Unknown error at address 0x0E
Unknown error at address 0x0F
Unknown error at address 0x10
Unknown error at address 0x11
Unknown error at address 0x12
Unknown error at address 0x13
Unknown error at address 0x14
Unknown error at address 0x15
Unknown error at address 0x16
Unknown error at address 0x17
Unknown error at address 0x18
Unknown error at address 0x19
Unknown error at address 0x1A
Unknown error at address 0x1B
Unknown error at address 0x1C
Unknown error at address 0x1D
Unknown error at address 0x1E
Unknown error at address 0x1F
Unknown error at address 0x20
Unknown error at address 0x21
Unknown error at address 0x22
Unknown error at address 0x23
Unknown error at address 0x24
Unknown error at address 0x25
Unknown error at address 0x26
Unknown error at address 0x27
Unknown error at address 0x28
Unknown error at address 0x29
Unknown error at address 0x2A
Unknown error at address 0x2B
Unknown error at address 0x2C
Unknown error at address 0x2D
Unknown error at address 0x2E
Unknown error at address 0x2F
Unknown error at address 0x30
Unknown error at address 0x31
Unknown error at address 0x32
Unknown error at address 0x33
Unknown error at address 0x34
Unknown error at address 0x35
Unknown error at address 0x36
Unknown error at address 0x37
Unknown error at address 0x38
Unknown error at address 0x39
Unknown error at address 0x3A
Unknown error at address 0x3B
Unknown error at address 0x3C
Unknown error at address 0x3D
Unknown error at address 0x3E
Unknown error at address 0x3F
Unknown error at address 0x40
Unknown error at address 0x41
Unknown error at address 0x42
Unknown error at address 0x43
Unknown error at address 0x44
Unknown error at address 0x45
Unknown error at address 0x46
Unknown error at address 0x47
Unknown error at address 0x48
Unknown error at address 0x49
Unknown error at address 0x4A
Unknown error at address 0x4B
Unknown error at address 0x4C
Unknown error at address 0x4D
Unknown error at address 0x4E
Unknown error at address 0x4F
Unknown error at address 0x50
Unknown error at address 0x51
Unknown error at address 0x52
Unknown error at address 0x53
Unknown error at address 0x54
Unknown error at address 0x55
Unknown error at address 0x56
Unknown error at address 0x57
Unknown error at address 0x58
Unknown error at address 0x59
Unknown error at address 0x5A
Unknown error at address 0x5B
Unknown error at address 0x5C
Unknown error at address 0x5D
Unknown error at address 0x5E
Unknown error at address 0x5F
Unknown error at address 0x60
Unknown error at address 0x61
Unknown error at address 0x62
Unknown error at address 0x63
Unknown error at address 0x64
Unknown error at address 0x65
Unknown error at address 0x66
Unknown error at address 0x67
Unknown error at address 0x68
Unknown error at address 0x69
Unknown error at address 0x6A
Unknown error at address 0x6B
Unknown error at address 0x6C
Unknown error at address 0x6D
Unknown error at address 0x6E
Unknown error at address 0x6F
Unknown error at address 0x70
Unknown error at address 0x71
Unknown error at address 0x72
Unknown error at address 0x73
Unknown error at address 0x74
Unknown error at address 0x75
Unknown error at address 0x76
Unknown error at address 0x77
Unknown error at address 0x78
Unknown error at address 0x79
Unknown error at address 0x7A
Unknown error at address 0x7B
Unknown error at address 0x7C
Unknown error at address 0x7D
Unknown error at address 0x7E
No I2C devices found


To make it even worse, I don't know why but when I switch the SDA with the SCL and then switch them back, suddenly it works and the I2C scaner finds both, the PN532 (0x24) and the LCD (0x27).

Does anyone have any clue on why is this happening?

Please help me, I've been struggling for days now and can't find the answer