Fixme.ch:OldWiki/Magnetic Cards

Raspberry pi (CMOS <- TTL level voltage attenuation)

The "level converter" in this case is only needed to convert from 5V to 3V3 levels, and can consist of a simple voltage divider. the 3V3 level from a CMOS output needs no conversion for most 5V inputs.

You can create a simple attenuator to 3V by using a top 2K2 (2.2k) and a bottom 3K3 resistor, it will work even at high speeds, because the GPIO input is high impedance and its capacitance is relatively low, so the signal isn't degraded much.[1]

           2K2
  5V in ——/////—+— 3V out
           3K3  |
   GND  —–/////—-

Liens divers

http://bit.ly/lf1XQY

http://bit.ly/lE5NaZ