The Power Supply

You will definitely need a regulated 5-volt power supply to work with TTL chips. As mentioned previously, neither Radio Shack nor Jameco seem to offer a standard, inexpensive 5-volt regulated power supply. One option you have is to buy from Jameco something like part number 116089. This is a 5-volt power supply from an old Atari video game. If you look in the Jameco catalog, you will find that they have about 20 different surplus power supplies like this, producing all sorts of voltages and amperages. You need 5 volts at at least 0.3 amps (300 milliamps) -- you need no more than 2 amps, so do not purchase more power supply than you need. What you can do is buy the power supply, then cut off the connector and get access to the 5-volt and ground wires. That will work fine, and is probably the easiest path. You can use your volt meter (see below) to make sure the power supply produces the voltage you need.

Your alternative is to build a 5-volt supply from a little power-cube transformer. What you need is a transformer that produces 7 to 12 DC volts at 100 milliamps or more. Note that:

  • The transformer MUST produce DC voltage.
  • It MUST produce 7 to 12 volts.
  • It MUST produce 100 milliamps (0.1 amps) or more.
You may have an old one lying around that you can use -- read the imprint on the cover and make sure it meets all three requirements. If not, you can purchase a transformer from Radio Shack or Jameco.

Radio Shack sells a 9-volt 300-milliamp transformer (part number 273-1455). Jameco has a 7.5-volt 300-milliamp model (part number 149964). Clip the connector off the transformer and separate the two wires. Strip about a centimeter of insulation off both wires. Now plug the transformer in (once it is plugged in, NEVER let the two wires from the transformer touch one another or you are likely to burn out the transformer and ruin it). Use your volt meter (see below) to measure the voltage. You want to make sure that the transformer is producing approximately the stated voltage (it may be high by as much as a factor of two -- that is okay). Your transformer is acting like a battery for you, so you also want to determine which wire is the negative and which is the positive. Hook the black and red leads of the volt meter up to the transformer's wires randomly and see if the voltage measured is positive or negative. If it is negative, reverse the leads. Now you know that the wire to which the black lead is attached is the negative (ground) wire, while the other is the positive wire.

Using a Volt-Ohm Meter
 A volt-ohm meter (multimeter) measures voltage, current and resistance. It has two "leads" (wires), one black and one red. What we want to do with the meter right now is learn how to measure voltage. To do this, find a AA, C or D battery to play with (not a dead one). We will use it as a voltage source.

Every meter is different, but in general, here are the steps to get ready to measure a battery's voltage:

  1. Take your black test lead and insert it in the hole marked (depends on the meter) "Common," "Com," "Ground," "Gnd" or "-" (minus).
  2. Take your red test lead and insert it in the hole marked (depends on the meter) "Volts," "V," "Pos" or "+" (plus). Some meters have multiple holes for the red lead -- make sure you use the one for volts.
  3. Turn the dial to the "DC Volts" section. There will usually be multiple voltage ranges available in this section -- on my meter, the ranges are 2.5 volts, 50 volts, 250 volts and 1,000 volts (fancy auto-ranging meters may set the range for you automatically). Your meter will have similar ranges. The battery will have a voltage of 1.25 volts, so find the closest voltage greater than 1.25 volts. In my case, that is 2.5 volts.
Now, hold the black lead to the negative terminal of the battery and the red lead to the positive terminal. You should be able to read something close to 1.25 volts off the meter. It is important that you hook the black lead up to negative and the red lead up to positive and stay in the habit of doing that.

Now you can use the meter to test your power supply, as well. Change the voltage range if necessary and then connect the black lead to ground and the red lead to what you presume to be the positive 5-volt wire. The meter should read 5 volts.