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-- More Hacking and Stuff
-- Page: 1 2 3 4

   An opening note:

   Please don't try to build this if you have never tried anything of the sort and are unwilling to accept a $20 loss. It is possible that you will not be able to make this circuit work at all, and you wont be able to return the parts afterwards. If you are completely willing to lose 20 bucks and are able to pay close attention to detail, then this shouldn't really be that hard for you. Don't jump to the final schematic unless you know something about electronics or have some experience building this kind of stuff. It can be very intimidating at first glance.

   At the end of this guide I have included several building and troubleshooting tips. However, I cannot possibly foresee every problem that every person will have. Therefore, if you can't get yours to work, feel free to post on the GideonTech Forums about it. It'll probably get around to me anyway. Do not try to email me or call me or visit me or whatever. Especially do not hold me responsible for any losses you may incur by trying to build this.

   In fact, I'm just gonna say it. YOU CANNOT HOLD MYSELF, GIDEONTECH, OR ANY OF THE EMPLOYEES OF GIDEONTECH RESPONSIBLE FOR ANYTHING THAT HAPPENS AS A RESULT OF YOU READING THIS GUIDE OR TRYING TO BUILD THIS CIRCUIT. Sounds kinda glum, but I just don't want any angry messages saying that I said it was easy and that anyone could do it. Just follow directions, take your time, and be safe (NEVER make any changes or touch any components when the power is turned on) and you should be okay. Have fun with it!

   Parts List

   First of all, keep in mind that if you can't find the exact value for a resistor, you can buy several resistors and hook them in series. This way, their total value is equal to the sum of each resistor. e.g. if you need 5k and the store doesn't have it, you could buy 5 1k resistors and hook um in series to make 5k. You can do the same thing with pots. You CANNOT do this with capacitors. Caps must be hooked in parallel for this to work.

   Make sure that every part has at least a .15-watt rating I used .25 watts just to be safe. However, don't go over .5 watts even .25 is overkill, and higher tolerance parts are more expensive.

   Also, make sure that you know that you are operating at 5V, so if any parts come up that have a voltage rating (i.e. the caps) you get one that wont fry.

   Resistors:

  • 220 ohm X 3
  • 360 ohm
  • 1k ohm
  • 3k ohm
  • 5k ohm
  • 8.2k ohm
  • 10k ohm
  • 15k ohm

   Make sure all resistors are accurate to within 5% (i.e. the last band in the resistor color code is gold)

   Capacitors:

  • 4.7 uf
  • 47 uf
  • 100 uf

   Potentiometers (pots):

  • 10k ohm
  • 20k ohm
  • 30k ohm

   Note: you'll pay an arm and a leg if you don't get trimmer pots. Shoot for something in the .25 watt tolerance range and you should be ok.

   ICs:

  • 555 timer IC X 3
  • 7400 digital logic IC (AND gates)
  • 7486 digital logic IC (XOR gates)

   Misc supplies:

  • Soldering iron
  • Solder
  • Wire
  • Sockets for the ICS
  • Molex Connector
  • An AT or ATX power supply (or any other 5V supply)
  • Circuit board (not really required, but makes life about 8.4 X 10^42 times easier, I recommend using a circuit board with a little dot of metal around each hole- this way the solder will bond with the board)
  • Prototyping equipment (also not required, but recommended- a breadboard allows you to build the circuit quickly and troubleshoot it easily)

   Important URLs:

   Please note that data sheets are very technical. Don't worry about them unless you want additional data on the chips. Also, I copied and modified the pinouts from these sheets, and in no way try to take credit for their creation.

Click to Enlarge

   Note: All of the information below can be found on the various data sheets listed above and at the 555 timer tutorial page. I recommend you visit the 555 page, but it isn't necessary. I tried to include everything you NEED to know to build the circuit in this text. You can build the circuit without knowing this stuff, but it helps to know this when it comes to troubleshooting.

   555 circuit:

Click to Enlarge

   The 555 is an IC that, at least how it's used here, produces a square wave with a frequency that is determined by the resistors and the capacitor that are in the circuit (in case you want to know, the formula is f=1.44/[{Ra+2Rb}*c]). For more on square waves, see the next section.

   Preliminary simulation: Be forewarned, this is kind of a stream of thought - I was trying to describe how I thought while I designed it while giving some info useful in building, and I think I might have failed.

Click to Enlarge

   This is the first simulation I did of the circuit. The bottom window shows the signals produced by the 555, some of the intermediate signals, and the final output. Each of the rectangles with a square wave on it represents one 555 circuit, which is a bit more complex than a box. The basic idea is that I use one 555 timer to sample another that is working at a different frequency, and the resulting signal is kinda random (not random cryptologically speaking, but it looks random enough). The third oscillator is to make it that instead of staying on for a bit and then turning off, the light flickers for a bit and then turns off. I used three logic gates- two XOR gates and one AND gate. When the wave is high, at the point being monitored the voltage is at its high point, which in my design is 5V- this is 1. When it's low, the voltage is zero and so is the state- this is 0. If and only if (iff) both inputs to the AND gate are 1, the output is 1. In all other cases the output is zero. Iff the inputs to an XOR gate are different, the output is 1. If the inputs happen to be the same (either 1 and 1 or 0 and 0) the output will be off. Therefore, I use the XOR gates to compare the 555's to each other. If just the short timer were there, the light would always blink at the same rate and would never turn off. The medium timer can turn off the light, but again this interval wouldn't be random. The long timer can be used in conjunction with the medium timer to simulate a random signal- actually, I could have just used the medium and long timers to determine when the signal would be off or on, and eliminate a logic gate from my circuit. However, I found that this didn't produce as random a flicker pattern, so I left it as it is (it doesn't really matter anyway, since the 7486 IC has four gates on it).

   Final schematic:

   The final schematic shows all three 555 circuits and the logic gates. However, it does not show the ICs and their pin outs as you will need to assemble them. In order to help clarify this, I will include the pin layouts for all of the IC's used in this project in addition to links to data sheets for each IC.

   7400 Pinout:

Click to Enlarge

   7486 Pinout:

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