Introduction: 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.


abzza made it!(author)2017-07-17

Fantastic! I made a similar design, then discovered yours and tweaked it to suit my needs. I made an instructable on my remix here:

Sunnyhiht made it!(author)2016-11-02

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...

russ_hensel made it!(author)2015-03-14

Just a note to let you know I have added this ( a year ago ) to the instructable:

Comprehensive Guide to Electronic Breadboards: A Meta Instructable


Take a look at a bunch of project involving breadboards.

Olivierh made it!(author)2014-03-11

if you don't want to build it yourself, there is cheap power supplies on the internet and I think that would be cheaper

charge11595 made it!(author)2014-02-09

Awesome! Built this over the week end with a few additions, including a heat sink, wire terminals, and a 14 pin ic socket so that I could change the resistors. I'm hoping to add a trimmer potentiometer some project enclosure later as well.

BTW, the resistors in the image are only place holders until I find the ones I need.

alien9999 made it!(author)2012-08-10

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.

F-zero made it!(author)2009-06-23

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!

Radioactive_Legos made it!(author)2011-04-18

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 :)

oldskooldawgz made it!(author)2011-02-16

y are there two 240 ohm resistors slot 22 n 23

beehard44 made it!(author)2011-01-03

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

jomac_uk made it!(author)2011-01-02

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!

hokie88 made it!(author)2010-09-01

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

David_C made it!(author)2009-05-04

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.


dagenius made it!(author)2009-11-10

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.

wkuace made it!(author)2010-08-25

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

Minifig666 made it!(author)2009-12-05

 Would a 12v 2000mA power supply be capable of powering this unit?

kikiclint made it!(author)2010-08-25

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.

geeklord made it!(author)2009-01-18

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

beehard44 made it!(author)2010-04-18

grab a free sample from ti

Artificial+Intelligence made it!(author)2008-05-30

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.

Derin made it!(author)2008-08-20

seems like a short

Artificial+Intelligence made it!(author)2008-08-20

It can't be, cause it works fine and I've checked the circuit board.

kersny made it!(author)2008-08-20

Make sure that your input voltage is not insanely higher than your output voltage(12v in for 3.3v out). Also, a heatsink helps if you don't already have one.

Artificial+Intelligence made it!(author)2008-08-20

That could be the problem. I supply it with 24 volts.

dagenius made it!(author)2009-11-10

yes, that would be it. voltage regulators regulate by turning the excess power into heat, and 24 volts to 3 volts would mean it would be dissipating 21 volts into heat. bad.

beehard44 made it!(author)2010-04-18

use a heatsink
i used the TO-92 package from Texas instruments. best of all, it was FREE!

Minifig666 made it!(author)2009-11-28

 Can I ask what the diodes are for and why do you need two?

Minifig666 made it!(author)2009-11-28

 Sorry I meant 4. Are they for AC/DC Conversion

beehard44 made it!(author)2010-04-18

i think he was using ac, so he needed to convert it

thestyrofoampeanut made it!(author)2010-03-08

 the tape is a great idea
i always used to put in components and bend the wires down so they would stay still

Xellers made it!(author)2009-11-11

An excellent project - but I would personally prefer to use a potentiometer to regulate the voltage coupled with an analog voltmeter.

reaman4ever made it!(author)2009-04-26

how do you make connections from one point to another on a board like this (where none of the points are connected)? Do you drag the solder somehow? is there some kind of trick? I bought a whole bunch, but dont know how to use them. thanks

dagenius made it!(author)2009-11-10

yeah, you creat solder bridges, use jumpers, and wires on the bottom as well.

MrNintendo made it!(author)2008-12-04

Sweet instructable man. I've needed one of these for a good while, just now decided to see if anyone made these. One question though, on step 14, in the main pic, you said that 2 of the diodes were facing the wrong direction, but does it really make any difference? It might be a stupid question, but I'm still in high school, so I dont know much of this stuff, mind helpin me out?

Swishercutter made it!(author)2009-11-09

That might help explain the current flow in a bridge rectifier for you.  Basically, it converts the AC signal to a pulsating DC signal (the capacitor on the bridge output smooths the pulses).

rcguymike made it!(author)2008-12-22

It does matter because diodes allow current to only flow in one direction. It comes out the end with the stripe and in the other. If you hook it up backwards it won't allow the current to flow.

ElectronMad made it!(author)2009-08-12

Yea umm Nice... May i give a tip? Instead of using 8 pins just get 4 But how? simple Get a needle nose plier and you no the black part make it go to the very top! Put it through And solder it then take of the black thing and put it on the front if wished keep on the top..

agis68 made it!(author)2009-02-02

Nice job and well done. U mean the Radishack Console that one costs 70$? I was ready to order it but thanx to u i got it

FreeBaseBuzz made it!(author)2009-05-24
huitlacoche made it!(author)2009-04-24

What is the purpose of using 4 rectifying diodes instead of one and what is the advantage of having them in parallel? I'm not sure I really understand how they are wired by looking at this schematic.

huitlacoche made it!(author)2009-04-24

Okay, thats a full-wave rectifier. I should've done the research *before* asking the question. Oh well.
I figured this was just accepting a DC voltage source. But the rectifier will allow for AC now?

bombmaker2 made it!(author)2009-03-03

wat is the imput?

the+judge made it!(author)2009-02-08

I accidentally reversed the power supply pins and blew up a capacitor :( what are the upper and lower limits on the capacitor voltages (I'm assuming 24v) and capacitance for this to work? I can't find a ceramic disk capacitor that has enough description on it for me to find spec on them ( I get most of my components from old tech like stereos). the most description I could find on any of them was a 3 digit number or a voltage rating, but no capacitance rating, but I did find a film capacitor that has .1 uf, could I use that?

sarahsyakirah made it!(author)2009-01-27

what would be the resistance of the device that connected to the output terminal of voltage divider?? please answer me..

rinthesun made it!(author)2009-01-17

Problem: If the power supply is in circuit and all switches are turned off almost the full wart voltage is connected to the breadboard. It would be safer to have the resistors in series with a shunt. Of cause the resistor error would be more of a problem.

Barney+Watches+You made it!(author)2008-08-30

this is an awesome idea! I'm going to make one.

Unit042 made it!(author)2008-07-17

Clever stuff! Using a series of switches to vary the voltage divider. Usind a dipswitch is fine, but what's wrong with a 10k pot? <br/>My power supply is a mystery transformer outputted to a heavy duty overkill full wave bridge rectifier which goes to a <a rel="nofollow" href="">LM2937</a>.<br/><br/>I get 12-15v from transformer, and regulated 5v from, well, the regulator. Oh, and don't forget GND!<br/><br/>PS: It may be common knowledge among 'iblers (people who make 'ibles), but is there any way I can see a higher resolution and larger size version of the images i.e. schematics?<br/>

lifelong-newbie made it!(author)2008-08-15

You can see some different size scalinngs of the pictures by clicking the i in the top left corner of the pic and selecting the image size you want.

Unit042 made it!(author)2008-08-19

Cool. Thanks!

Unit042 made it!(author)2008-07-17

Nice soldering! Did you do it nice and pretty just for the 'ible? Mine isn't pretty but it gets the job done.

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