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How Electronic Gates Work

Assembling Your Equipment
A resistor and an LED
A resistor and an LED

In order to play with TTL gates, you must have several pieces of equipment. Here's a list of what you will need to purchase:

  • A breadboard
  • A volt-ohm meter (also known as a multimeter)
  • A logic probe (optional)
  • A regulated 5-volt power supply
  • A collection of TTL chips to experiment with
  • Several LEDs (light emitting diodes) to see outputs of the gates
  • Several resistors for the LEDs
  • Some wire (20 to 28 gauge) to hook things together

These parts together might cost between $40 and $60 or so, depending on where you get them.

Let's walk through a few details on these parts to make you more familiar with them:

  • As described on the previous page, a breadboard is a device that makes it easy to wire up your circuits.
  • A volt-ohm meter lets you measure voltage and current easily. We will use it to make sure that our power supply is producing the right voltage.
  • The logic probe is optional. It makes it easy to test the state (1 or 0) of a wire, but you can do the same thing with an LED.
  • Of the parts described above, all are easy except the 5-volt power supply. No one seems to sell a simple, cheap 5-volt regulated power supply. You therefore have two choices. You can either buy a surplus power supply from Jameco (for something like a video game) and use the 5-volt supply from it, or you can use a little power-cube transformer and then build the regulator yourself. We will talk through both options below.
  • An LED (light emitting diode) is a mini light bulb. You use LEDs to see the output of a gate.
  • We will use the resistors to protect the LEDs. If you fail to use the resistors, the LEDs will burn out immediately.

This equipment is not the sort of stuff you are going to find at the corner store. However, it is not hard to obtain these parts. You have a few choices when trying to purchase the components listed above:

  1. Radio Shack
  2. A local electronics parts store - Most major cities have electronics parts stores, and many cities are blessed with good surplus electronics stores. If you can find a good surplus store in your area that caters to people building their own stuff, then you have found a goldmine.
  3. A mail-order house like Jameco - Jameco has been in business for decades, has a good inventory and good prices. (Be sure to download their PDF catalog or get a paper catalog from them -- it makes it much easier to traverse the Web site.)


  • *Jameco also has "assorted LEDs" (or grab bags) that are much cheaper on a per-LED basis. Look around and see what's available. This is one place where a surplus electronics shop will have much better prices.
  • If you are shopping at Jameco, you may want to get two or three of each chip just in case -- they only cost about 30 cents each. You might also want to purchase an extra 7805 or two.
  • You will also need a pair of wire cutters and wire strippers. In a pinch, you can use scissors and your fingernails, but having the proper tool makes it easier. You can get wire cutters and wire strippers at Jameco, Wal-mart, Radio Shack, and tons of other places. I also find that a small pair of needle nose pliers is helpful at times.