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.

Step 1: The LM317

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

Step 2: Calculating the Values

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


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


I chose the following power values for my power supply:

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

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

Step 3: The Parts

Barrel Jack--------------------------------Salvaged
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

Step 4: The Tools

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

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

Step 5: The Schematic

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

Step 6: Build It!

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

Step 7: Cutting the Breadboard Strips

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.

Step 8: The Board Layout

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

Step 9: The Barrel Jack

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.

Step 10: Build It!

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

Step 11: Marking the Parts Placement

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

Step 12: Soldering the Resistors

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.

Step 13: Soldering the Capacitors

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.

Step 14: Soldering the Diodes

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.

Step 15: Soldering the Power Switch

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.

Step 16: Soldering the Barrel Jack

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.

Step 17: Soldering the DIP Switch

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

Step 18: Soldering the Regulator

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

Step 19: Breadboard Connections

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.

Step 20: Connecting Everything Together

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.

Step 21: Test It

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

2 People Made This Project!


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64 Discussions


2 years ago

i have to make a variable power supply ranging from -12v to +12v dc output from 240v ac wall input... i am using LM317 and LM337 ... please help me out with the transformer ratiing to be used and which rectifiers diode to be used and values of capacitors and resisters...


6 years ago on Introduction

I have couple of questions. It's obvious that he used AC current at input, but how much voltage is on input ? I made this project with same resistor values but I power it with adjustable DC adapter (12V 1500 mA). So my problem is that I don't get the the voltages I suppose to get on output ( they are smaller). Also if I put smaller voltage on input (for example 9V) output will be even smaller. So final question is: how much voltage should power this circuit so I can get proper voltages on output? Help would be appreciated.
By the way, very practical project.


9 years ago on Introduction

Great job on this! I made one for myself and it works great! I altered it a bit though.I made my own PCB board for it. Also, I added a fuse and a diode to be on the safe side and I replaced the 4 rectifying diodes with a bridge rectifier. I also added the little wire clip thing instead of placing it directly into the breadboard. I learned alot while making this. Thank you very much! One last note, when the switches on the DIP-8 aren't turned on, the output power 35 volts. I don't know if its supposed to do that or its my board. But, other than that, it works like a charm. Thanks!

1 reply

I found the same with mine in regards to the output voltage when no switches are on. I think it's because you use a larger resistor for R2 to raise the output voltage, so when none of the switches are on, it effectively raises the value of R2 to infinite resistance, putting out the max voltage possible. Since your output in that situation is 35V, I would assume that your input is somewhere around 37VDC :)


8 years ago on Introduction

looks like the voltages are a little bit off. Why not use presets and calibrate so that you get the right voltages


8 years ago on Step 5

I like the switch idea, once set up, its a simple matter of selecting the voltage, without having the hassle of connecting up your volt meter, all in all its a good instructable!


8 years ago on Step 5

Works great thanks man, I used a dc input source so i got rid of all the diodes and didnt bother with the switch, I wish they made a much larger 8 rocker switch


10 years ago on Introduction

There are 3 of us guys who tinker around doing electronics projects and we watch the youtube video by Kip Kay about getting Free Electricity from your phone line which is between 40~75 Volts ac and Kip showed useing a Bridge Rectifier as the input then the voltage goes to the Lm317 voltage regulator.

So why couldn't you use this input voltage to power your projects once you know that value that the phone line produces, as in this example by useing the method he memtioned and adapting it to be a varabile power source by useing a 5k Trimmer pot and adding a volt meter to the circuit so you could fine tune it to a voltage of 3v, 5v, 6v, 7.5v, 9v, 12v ect.

heres the link the the Jpeg image i came up with

E-mail Address:

Please Comment on this circuit if you think it would work
by E-mailing me.


2 replies

Reply 9 years ago on Introduction

I saw that earlier, on the make podcast, and I tried measuring the power from the phone line, but we ended up having to replace all of my phone modules due to them frieing from the energy draw that my multimeter created.


Reply 8 years ago on Introduction

Also that is Illegal, and if the phone company notices what your doing they will shut off your phone and maybe sue you. If your want a cheap supply to power this circuit buy an old ATX supply from ebay they are about $10 and work great. There are instructables that show how to convert them to work outside of a computer Or you could go to consignment stores and look around for an old wall-wart power supply that will meet your needs, You can get a whole printer at Goodwill for $5 and their are lots of extra goodies inside


Reply 8 years ago on Introduction

It gives a maximum voltage about 2 volts below what you put in, so yes it would. You would then have a 10 volt power supply.


10 years ago on Introduction

i went to radioshack today, and they were all out of adjustable v-regs!!! I was a little upset....

1 reply

I've made this and it works great, nice job. There is one thing, I think is weird though, the LM317 heats up very fast. Even when it is powering a standard low power LED (10mA) it gets hot enough to melt plastic bags.

2 replies