cryptoarticles:

(via OPTO Contactless Payment Technology Is A FinTech Game Changer)

All of the encrypted payment data is transmitted through colour-encoded light signals, which use different frequencies to broadcast information to an optimal reader within the vending machine itself. This still requires merchants to upgrade their vending machines, but it removes the burden of obtaining the latest technology for the consumer.

From http://kianorshahmohammadi.com/post/148544415040

From https://dentaleconomicsus.wordpress.com/2016/08/06/cryptoarticles-via-opto-contactless-payment-technology-is-a/

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