The Radioshack, Adjustable, Breadboard Power Supply.

This Instructable will show you how to build an adjsutable breadboard power supply entirely from Radioshack parts. It can provide multiple voltages directly to the power rails on a prototyping breadboard. This could be useful for people on a low budget, who don't like to order parts online, or who need a good weekend project.

The LM317, according to Wikipedia, is
an integrated three-terminal adjustable linear voltage regulator. It supports input voltage of 3V to 40V and output voltage between 1.25V and 37V. It has a current rating of at least 1.5A although lower current models are available. Its output voltage is controlled by a resistor or a potentiometer. The LM317 also has a built-in current limiter as a safety feature. LM317 is manufactured by many companies, including National Semiconductor and Fairchild Semiconductor. The LM317 will automatically reduce output current if it gets too hot under load. The use of a heatsink is recommended to extend the part's power-handling capability. LM317 is a positive voltage regulator. Its negative complement is the LM337

This will provide the Power in our Power Supply. It can also be found at a well-stocked Radioshack.

National Semiconductor's page

The following formula will allow you to calculate the resistor values to set the LM317 to any voltage that you need:

R2=R1((V/1.25)-1)

A standard R1 Value is 240 Ohms, so the final formula is:

R2=240((V/1.25)-1)

I chose the following power values for my power supply:
1.5
3
3.3
4.8
5
6
9
12

So my resistor values are the following(some have two for greater precision):
47
330
390
680
330 390
820 100
1500
1800 270

All of these resistor values can be found in the Radioshack 500 Piece Carbon Film Resistor Assortment.

Barrel Jack--------------------------------Salvaged
Switch--------------------------------------275-409
Rectifying Diodes-----------------------276-1653
100uf cap----------------------------------272-1044
LM317T Voltage Reg.------------------276-1778
10uf cap-----------------------------------272-1025
.1uf cap------------------------------------272-135
Header Pins-----------------------------Salvaged
Prototyping Board----------------------276-0149
500 Piece Resistor Assortment---271-312A
Heat Sink--------------------------------276-1363
8 Position DIP Switch----------------275-1301B
Scrap PCB------------------------------Salvaged

These tools are common hobbiest items, most people should have:

Soldering Iron
Solder
Solder Wick
Wire (RS # 278-1221)
Multimeter
Various Pliers
Big Scissors
Duct Tape

This is your basic LM317 Schematic, with the DIP switch and the resistors added(Look at Notes!!):

The Following steps will detail the construction of this power supply.

Take your scrap PCB, and mark outside a 7x8 rectangle. Use your large scissors to cut inside this rectangle. You should now have a 6x5 box. Cut this down the middle of the short side, finishing with two 6x2 strips. These will connect the power supply to the breadboard. Set these aside.

If you have followed my parts list, you should be able to copy this layout for your board.

The Following pictures detail the steps of marking and drilling for the barrel jack. I used a 7/64 drill bit for the mounting holes.

The following Instructions will detail the construction of this power supply.

After you have the board layout completed, mark every part hole with a permanent marker so you can easily stuff the board.

Remove all of the components except for the resistors. Place a piece of Duct tape over all of the resistors, holding them to the board. Turn it over, and solder each of the leads to the board. Finally, cut all of the component's leads off and remove the tape.

Place the capacitors in their positions, noting polarity, and put the tape over them. Flip it over, solder the components, clip the leads, and remove the tape.

Mostly the same as the last step, and remember to note polarity. LOOK AT THE PICTURE NOTES. Put them in their places, put tape over them, solder, clip, and remove the tape.

Put the switch in place, it shouldn't need to be taped. Flip it over, solder, cut the leads, and flip the board back over.

This is probably the hardest part to solder, because the jack required me to drill out the pad, You have to solder to a nearby pad. You shouldn't need tape for this, and all the soldering steps are the same.

Again, more soldering. Tape the DIP switch in place, solder, remove tape.

Final Part!! Put the regulator in, tape it, solder it, cut the leads, And your done!

To connect the power supply to the breadboard, use 8 header pins and your 2x6 strips. Solder 2 sets of 2 header pins to the board where it will plug into the breadboard. Solder the strips to these, then solder the other header pins onto these strips, upside down. The pictures help explain the concept better. Also, I used resistor leads to connect the two header pins.

The following schematic shows which connections are to be intentionally bridged and which are to be connected with jumpers. The other pictures show my connections.

Your Done!!! Now that you have the power supply assembled, test every voltage to see if it is close enough to your desired voltage.