We have something a bit more advanced for you today to work on for you computer.  This guide will allow you to replace your power button with a perforated coded card, giving the possibility to “lock” your computer.  People won’t be able to turn it on nor off via hardware. 

If you want to power up or shut down your PC, all you have to do is insert the card and take it out.  The size of the coded card depends on the size of the materials and you.  I’ve chosen to use an optic reading circuit together with a perforated card containing a code because all you’ll see is a little slit wherever you put the reading circuit.

The reading circuit can be away from the circuit that is in charge of the lock.  With a coded card you don’t need to remember or type numbers compared to a numeric pad.  Having only some ICs you can have a huge number of possible combinations.  The circuit I’m about to describe has 255 possible combinations, I’ve asked in the forums and this is what most people requested.

   This is an “Advanced” guide, you may not be able to get the same parts as I did. The locking circuit has already been tested and works with all the parts listed. If you cannot get the same parts, I recommend having a multi-tester, although an oscilloscope is going to be the best choice since you’re going to be able to see exactly what’s happening.  It’s important to read everything in this guide, so if you’re having some troubles you may be able to check what’s wrong. Knowledge about electronics and digital logic will definitely help you.  You will also have to find an optoisolator that fits the circuit and your motherboard (Voltage and Amperage), since the original project I did used a relay and I couldn't test it with an optoisolator.  Don’t be scared by all you’ve just read, keep reading.

   Materials:

• 1 14015
• 2 14049
• 1 14081
• 1 14082
• 1 14106
• 5 Resistor 1K2O 1/4W
• 4 Resistor 100KO 1/4W
• 1 Experimental PCB
• 2 IC Socket 14 Pins
• 2 IC Socket 16 Pins
• 3 Capacitor 1nF
• 4 Phototransistor Brand: Kingbright – Model: L-32P2C
• 4 Infra Red Emitting Diode Brand: Kingbright – Series: L34
• 1 Optoisolator (You might also need a resistor for it)
• Ruler
• Pen or Pencil
• Soldering Iron Kit
• Drill
• Saw
• Hot Glue or any Epoxy
• Plastic Box
• Piece of Wood
• Card, you can use an old credit card or a phone card.
• Screws, Nails, or anything to make a rail for the card.