The readers works with 13.56Mhz tags and cards that support ISO14443A, MIFARE and NTAG.
I have mine reading and writing to cheep blank cards I found on ebay and programmed through the UIFlow environment.
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Just a caveat guys, beware that some vendors of the grove cables have the yellow and white wires switched so if you find your units aren't functioning correctly remember to check the cables first.
I tested a hub device attached to port A with a few 100cm grove cables and I was able to successfully read the i2c address of the ENV sensor and also others. I tested with the i2c_tester arduino program https://github.com/m5stack/M5Stack/blob/master/examples/Advanced/I2C_Tester/I2C_Tester.ino perhaps its just an isolated incident.
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