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-- How it Works
-- Page: 1 2 3 4

   PT: Phototransistor
   IRED: Infra Red Emitting Diode

   The circuit is powered with 12V, use the yellow and black wires of any of your molex connections.  The circuit in charge of reading the code contained in the coded card is a PT that works together with an IRED, these two are matched to work together.  The PT and IRED are connected to 12V by their resistors.  A 4106 was used between the 4015 and the PT because the PT is NPN. The 4106 was used as well with an RC circuit because the signal has a lot of noise that needs to be filtered.

   When the coded card is inserted and one of its perforations faces the PT and IRED, the PT receives the light coming from the IRED. When this happens, the PT sends a “0” from its collector which passes trough the 4106, the 4106 inverts that “0” and sends it to the 4015’s input as a “1”.  When the card isn’t inserted the 4015 is in “Reset” mode because the PT in charge of “Reset” is receiving the light coming from the IRED.  When you insert the coded card, the light going to the PT in charge of 4015’s “Reset” is blocked, enabling “Clock” and “Data” functions.

   The data is inserted in a serial way by “Clock” pulses.  When a perforation faces the PT and IRED in charge of 4015’s “Clock”, the 4015 represents at its “Q0” output the “Data” that existed at that moment, this can be “0” or “1” depending if the card’s sector that corresponds to “Data” is perforated or not. If there’s a perforation “Data” will be “1”, if there isn’t a perforation “Data” will be “0”.  As new “Clock” pulses are given, the data at the 4015’s output shift from “Q0” passing through its other outputs until it reaches “Q3”. The 4015’s outputs are directly connected to the 4082, or passing before through the 4049 depending on the combination you have previously chosen for the coded card.  When one data at the 4015’s output is “0”, we have to use the 4049 before we reach the 4082, so at the 4082’s input we are going to have a “1”.  When the previously chosen combination is the correct one, a “1” will be represented in all 4082’s inputs, representing a “1” at its output.  The outputs of the 4082 are connected to another AND gate but this time one of only two inputs and one output. Connected to the last AND gate’s output we have an optoisolator that is going to work as a switch, shorting or not the power pins of your mobo.  When the AND’s output is “1” the optoisolator will be shorting your power pins, when the AND’s output is “0” the optoisolator won’t short your power pins.  This basically will just turn your computer on or not.

   The clear "LEDs" are the PTs.  The bluish / greish "LED" is the IRED.  I've put a LED on the protoboard to show when the circuit was enabled or disabled.

   Sorry for the blurry pic, I couldn't use my camera's flash, it's too powerful, the LED's light wasn't visible and the flash also disabled the circuit when the Reset IRED detected the flash.

< Electronic Lock with Key Card

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