io devices barcode reader it shines a light, then more light reflects from the white than the black, then it uses that to read a string white is 0, black is 1 barcodes have a product number on the right and a manufacture number on the left the right hand side codes are writen through a not gate (inversed) qr codes the same as a barcode but 2d digital cameras they look at how much light enters the lens then depending on its color and brightness it will output a different value each pixel the camera outputs must have its own small light/color sensor lazer printer a negative static charge is put on paper puts ink down thats atractive to the negative charge rfid it sends some radio waves out, then reads the radio waves sent back some devices require active power, while other can get power from the incoming radio waves