Instructables

The Radioshack, Adjustable, Breadboard Power Supply.

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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.

 
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Step 1: The LM317

Picture of 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

Picture of Calculating the Values
DSCN0559.JPG
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.

Step 3: The Parts

Picture of The Parts
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

Step 4: The Tools

Picture of The Tools
DSCN0578.JPG
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

Step 6: Build It!

The Following steps will detail the construction of this power supply.
Olivierh5 months ago

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

http://voltatek.com/en/home/27-breadboard-power-su...

charge11595 made it!6 months ago

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.

photo.JPG
alien99992 years ago
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-zero5 years ago
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!
0623091519.jpg
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 :)
y are there two 240 ohm resistors slot 22 n 23
ernie6663 years ago
why do u need capacitors?
beehard443 years ago
looks like the voltages are a little bit off. Why not use presets and calibrate so that you get the right voltages
jomac_uk3 years ago
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!
hokie884 years ago
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_C5 years ago
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.

http://www.youtube.com/watch?v=WoaLGvJkoP8

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

http://i247.photobucket.com/albums/gg149/davidmann007/LM317withBridgeRectifierCircuit-1.jpg

E-mail Address:
Treasurehunterenterprizes@yahoo.com

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

Sincerely
Dave
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 dagenius4 years ago
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
Minifig6664 years ago
 Would a 12v 2000mA power supply be capable of powering this unit?
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.
geeklord5 years ago
i went to radioshack today, and they were all out of adjustable v-regs!!! I was a little upset....
grab a free sample from ti

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.
seems like a short
It can't be, cause it works fine and I've checked the circuit board.
kersny (author)  Artificial Intelligence6 years ago
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.
That could be the problem. I supply it with 24 volts.
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.
use a heatsink
i used the TO-92 package from Texas instruments. best of all, it was FREE!
Minifig6664 years ago
 Can I ask what the diodes are for and why do you need two?
 Sorry I meant 4. Are they for AC/DC Conversion
i think he was using ac, so he needed to convert it
 the tape is a great idea
i always used to put in components and bend the wires down so they would stay still
Xellers4 years ago
An excellent project - but I would personally prefer to use a potentiometer to regulate the voltage coupled with an analog voltmeter.
reaman4ever5 years ago
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
yeah, you creat solder bridges, use jumpers, and wires on the bottom as well.
MrNintendo5 years ago
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?
hyperphysics.phy-astr.gsu.edu/Hbase/electronic/rectbr.html

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).
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.
ElectronMad5 years ago
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..
agis685 years ago
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
huitlacoche5 years ago
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.
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?
bombmaker25 years ago
wat is the imput?
the judge5 years ago
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?
what would be the resistance of the device that connected to the output terminal of voltage divider?? please answer me..
rinthesun5 years ago
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.
this is an awesome idea! I'm going to make one.
Unit0426 years ago
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="http://www.solarbotics.com/products/lm2937/">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/>
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.
Cool. Thanks!
Unit0426 years ago
Nice soldering! Did you do it nice and pretty just for the 'ible? Mine isn't pretty but it gets the job done.
wbornor6 years ago
what tool do you use to draw your schematics?
kersny (author)  wbornor6 years ago
I use cadsoft eagle from cadsoft.de. Its hard to get started, but once you get used to it, it works really great. Sparkfun.com has some great tutorials on the subject.
dean-1016 years ago
can some one please help me. i need a power supply (a uk adopter) for running all the projects i make but i have a lot of adopters laying around and i dont no if they are safe to use. would a 5.2v 100ma be safe to use if i cut the end off and use croc clips? or a 3-20 v 3000ma bench top power suply? if none of these will be safe can anyone tell me one that will be safe plus could they do damage or shock you if i touched the ends by mistake?? please help thanks
I took two 9V batteries and connected them in series for a super-bright LED flashlight. Their drawing about 36 mA 100 mA wont shock you, im not sure wether the other one will, better to be safe than sorry what is that charger for? i cant find one that outputs less than 1000mA
it was off an old drill battery charger. weird thing is that the 5v charger was used to charge a 9.6v drill, but it worked fine. the 3000ma one is a desktop power supply i can get for £20 and it has different voltages that you can change
dfowler74376 years ago
I did a simular power supply design with the bridge rectifier. I did not put a dip switch to select the ouput voltage but I did bring out the adjust pin so that it could be done on the breadboard.

http://www.uchobby.com/index.php/2008/02/19/bread-board-power-supply/
gschoppe6 years ago
If you build this project for use with any sort of sensitive electronics, you may need a VOLTAGE REGULATED input... most cheap wall-worts' voltages will vary wildly depending on the load placed across them... using an unregulated wall-wort as input could fry your delicate (read: expensive) components, depending on the specifics of the LM317.

It looks like your minimum input is 28v (from the Nat-Semi diagram)... How well does the LM317 turn that into smooth power, over varying loads? does it internally regulate, or will output vary based on input voltage?

sorry, my Spidey Sense is tingling... or I'm being electrocuted... its always one of the two.
kersny (author)  gschoppe6 years ago
The Lm317 is just like a 7805, only with a voltage output dependent on the Resistor values(as shown in the schematic). From what I understand, it would be as reliable as a 7805, which is used to charge sensitive USB devices. I have been using it frequently since I first built it, and I have seen no problems with many different wall-warts on many different projects.
fjr1227 years ago
This is a really incredibly good instructable, the instructions and photos are properly detailed and every step is clearly layed out. Additionally this is a project I've always wanted to build (but didnt have the design skills). :)
kersny (author)  fjr1227 years ago
Thanks, but I don't think it's popular enough to win the laser cutter.
eh, good enough. all us geeks know the REAL useful stuff, most wannabe-electronics hobbyists attention is cought by the word 'LED" or "easy project" or "...for beginners" lol.
deva7 years ago
Euhm, am I missing something here, or ... When you add a load to your voltage divider, you'll change the overall resistance of the circuit (R1*R2/(R1+R2). This will change your voltage, or am i wrong ?
kersny (author)  deva7 years ago
I'm not sure what you mean? To change the output voltage, you have to connect resistance between The output and the adjust, or between the adjust and ground. You should be doing neither of these things by adding load to the circuit.
deva kersny7 years ago
What I mean is: You have 2 resistors, both of 100k for example you put them in series (voltage devider). when you put a circuit in parallell with one of the resistors, the resistance of that part will (most likely) have a resistance wich is less than 100k example: 100 K in paralell with 100 K gives a resistance of 50 K. Put this in your voltage devider, and you'll get: 100 and 50K in series, thus your output voltage between the terminals of the network has changed
Myself7 years ago
Nice design, I love the bridge rectifier feeding the regulator! Kinda idiot-proofs it. It's a shame you can't get nice pushbutton rotary switches (like the old SCSI ID switches) at RS these days! It'd be fun to mechanically click the voltage up and down a step at a time. So hey, with the DIP switches, I guess you unplug the supply before changing voltages? If you engage two rockers at once, that lowers the resistance which lowers the voltage, right?
kersny (author)  Myself7 years ago
You can change the voltage while the supply is on, but you must remember that when no switches are on, it will output the voltage of the Wall-Wart.
coil10027 years ago
You know I have been soldering for years and never once has it dawned on me to tape the components to the board. Thanks