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Bread Board Power Supply

OnBreadboard uCHobby’s first electronics kit is a handy breadboard power supply. The power supply design is simple but just what I needed for my electronics projects. I have seen several similar power supply boards but none had all the features I wanted. This design was also a good first project to help me learn about Kicad.

The board and parts are available as a kit from Curious Inventor now. I also plan to give away some of these kits as I have done in the past with the Arduino boards. There are more options in the giveaways specified at the end of this article as well.

I have been working on this power supply design for a short while. I wrote about the PCB pre-order check and the adjustable current sink I used to test the design in previous articles. I used Kicad for the schematic capture and PCB layout work and ordered the boards from Gold Phoenix as I had done with a previous project. During the design phase I used Octopart to locate the parts, data sheets, and prices.

Design Phase

I wanted a power supply that would be simple to build, inexpensive, and easy to use on a solderless breadboard. There are several similar modules available but none had all of the features I felt were important. While they are all very good designs, I wanted a few special features. To start my project I made a short list of requirements.

  • Headers plug into both power rails of the standard solderless breadboard with dual rails on both sides.
    • Some boards have different spacing so I went with a common version.
      • 1.65 inch spacing between inside power rails.
  • LED power indicator
  • Power Switch
  • Adjustable regulator so that I can set the desired voltage.
    • Must support 3, 3.3, 5, 6, 9, and 12V outputs
    • Adjustable at time of construction by selecting resistors
    • Short Circuit Protection
    • Overload Protection
    • LM317 regulator seems like the right choice given the requirements.
  • Design must be all through hole components
    • This module should be easy to build as a first project.
  • Have a screw terminal for power connection
    • Allows the use of any wall wart power supply
      • No concern about the matching connector, just cut the unnecessary connector off and insert the wires.
  • Full wave bridge input
    • No concern for power polarity
      • Can not be damaged by connecting power backwards
      • Works regardless of how power is connected.
      • Only concern is that your power source output at least 3V more then you want the module to output.
        • Need 8V to output 5V.
    • Accepts AC or DC power input
      • Again, just about any wall wart can be used.
  • Ground test point
    • A convenient location to clip your probe ground.
  • Inexpensive
  • Make use of open source design tools
    • Use Kicad for schematic capture and PCB Layout
    • Use Octopart for the parts selection

PartsPileThe module does include all the features listed above so I did meet the design goals. The picture here shows the board and parts ready to assemble. All through hole parts, bridge rectifier, screw terminals etc…

 

Kicad

Kicad was very easy to use for this project. I did have to create many of the PCB footprints and at least one schematic symbol but the process was very straightforward. The only problem I had was figuring out how to make the bottom layer into a ground plane. There is a great Kicad-users mail group and a quick search located the answer. Actually Phil, a uCHobby regular found this post with the answer and passed it on.

Schematic

The schematic below shows the bridge rectifier which allows for AC or polarity independent input connections. The regulator is an LM317 and input power is switched by SW1. I added two internal connections for the rectified but unregulated input supply and for the regulator adjust pin. A table showing the resistor pairs for various common voltages is included.

Unregulated power tap

The unregulated power connection is ideal for powering up devices that need a lot of current but are not sensitive to the exact voltage. Things like motors and relays can be connected here to keep the power dissipation in the regulator down. You could also connect another voltage regulator here to make a secondary supply.

Regulator adjust tap

If you need to make a current source or a variable supply then the adjust pin will be very handy. You can leave off one or both of the adjust resistors and adjust the supply voltage output from your breadboard.

Sch

PCB Layout

The layout work in Kicad was easy and straight forward. As you can see in the picture below, routing the board was simple. I wanted the bottom layer to be a ground plane but did end up running three traces in this layer. Kicad has a great feature that lets you fill a layer with copper after specifying which net you want connected to the fill. Just select the ground net and fill. Each connection to ground is thermally relieved as specified. All the other pads and traces are protected with a gap in the fill. The gap/relief and thermal relief are specified in an easy dialog before the fill is complete.

PCB

 

Octopart

I used Octopart to do my parts research. They have a fantastic search tool which gets you easy access to data sheets, pricing, and availability. Every time I use this tool, I like it more. I can not recommend it enough.

One nice feature for open source hardware projects is the ability to publish a parts list. The embedded version of my parts list is included below.

Performance

In this picture you see the assembled power supply mounted on my current sink breadboard. For input power I am using the wall wart from a scrounged Glade Light Show air freshener. I learned about this scrounging gem from an Instructable article and picked up a few. The Wall wart used to power the air freshener RGB LED and heater is rated to output 9VAC at 350mA. I cut the wires, stripped them and used the handy screw terminals to connect it to the power supply module. To test the module I set my current sink to draw about 300mA. At just above 300mA there was some ripple on the 5V output but this was due to the wall wart output dropping to below 8V under this load. I ran the module at this load for an hour or so. The regulator got very hot but did not shutdown.

Soaking300mA

Power Dissipation

The module should supply up to the maximum power specified by the LM317 regulator. The module is designed to allow for a heat sink as the regulator is mounted flush with the edge of the PCB. I recommend that you do use a heat sink if your need more then about 1/2 watt of dissipation in the regulator.  Power dissipation can be calculated easily, just multiply the voltage dropping across the regulator times the current used. In the example above, 9V input, 5V output is 4V drop. Actually the wall wart only output about 8V while loaded so the drop was 3V. At 300mA the 3V drop is about 1 Watt, (3 x 0.3 = 0.9 Watts).

Giveaway!

I will give away several of these modules. The same rules as specified in the original giveaway program apply as well as a few new ideas I want to try. In addition to the option of receiving one of these for a link to or an article published at uCHobby, I will send one to anyone who is credited with tipping another site about this article or to the first person that reports an error/typo in this article.

These new giveaway options are experimental and I might not be able to keep it up. If you have any doubt you can ask with a comment here or send me an email at dfowler@uchobby.com Please read the text below for some details before you post a comment or ask.

Reporting an error/typo:

Do not comment here with the typo! To get credit for the typo you must email me at dfowler@uchobby.com. I promise to give at least one module away to the first error/typo report but may give out several. Don’t hesitate to report anything you find that is actually an error. I don’t write perfectly and am not planning to give away kits due to poor grammar. I’m looking for errors and typos here.

Tipping a site to uCHobby:

This is another interesting experiment. I want to see uCHobby mentioned at other sites such as Make, who does watch this site. But there are other sites I may have not heard of or don’t know about uCHobby. Basically I will give away a few of these kits to people credited with tipping other sites about uCHobby. This is like paying you to help me get the word out and is similar to giving away kits in exchange for incoming links. As with the incoming links the tipped sites must be related to electronics hobby and you must claim the tip first. It must be easy to tell who did the tip and you must have sent the email with the link showing that the tip was posted before someone else does. I know this is a pain, I don’t know how to make it easier. For example, say you tip this article at Make, they will post up a note saying something like "David @ xyz tipped us to…" You send me an email, dfowler@uchobby.com, claiming that tip. I will reply letting you know if you got credit.

This is scary and I am trusting you to be fair and understanding on this one. I can see how this could be very bad as ten people might claim to be "David" You just have to trust that you will be first with the right combination to get the credit. If for some reason you are not first, please do not be upset. I will have no way to know for sure and will have to go with the first one to make the claim.

Receiving the kit:

If you are selected to receive a free kit, I will let you know by replying to your email message. You will need to send your mailing address at that point, you do not need to send your address prior to knowing that you will receive a kit. This is not a ploy to get your mailing addresses, email or home. I plan to update this area of the post with the selected winners names as well.

Again. these giveaway options are an experiment. Check back here or send an email to see how it progresses. If things don’t go well, I will delete this part of the article and the related comments. I will try to erase all evidence of the crazy idea…

Updates and more rules:

I will try to update the information as necessary. Of course you know all the legal mumbo jumbo that should be placed here. The most important thing is that I am doing the giveaways as a way to help promote this site, not to collect your personal information. I am not making any guarantees and may change the rules of this giveaway at any time. Again, check back here to check for updates. If you have any questions or suggestions please either post a comment or send me an email.

Update 1, 5:30 2/20/08

Five (5) typos/errors found so far. Joan, Brandon, Wayne, Daniel,  and another Wayne have all found errors or typos, kits will be shipping soon. So far "kits for errors" has been great. I wonder how many more errors will be found. Maybe this will teach me to do better proof reading.

Update 2, 1:30AM 3/1/08

Wow! a ton of typos and they keep coming in. I have to cry uncle at this point. Please do not stop sending messages with any flaws you find but I can not promise to give out more kits.

We have shipped out the typo giveaway kits. Please post a comment here when you get your kit. Let everyone know what you think about the kit etc…

The lesson learned here is that I need to do a much better job of proof reading. I
will work on my writing skill and I do plan to try the typo giveaway again. I wonder if it could work as a contest. Maybe with a higher value item, given away randomly each week to people that submit a typo or error report on any article. What do you think?

Posted in Parts, Projects, Workshop Tools.


47 Responses

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  1. aaa says

    Thank you for the nice article, but is there any chance you could repost the schematic without the background grid of points on it? It makes the schematic very difficult to read (especially considering the ultra-thin fonts it uses). Thanks!

  2. Bobocito says

    David,
    I got the kit a few days ago. Thanks, it looks like just about the right kind of project for my skill level.
    I hope to use the power supply in testing guitar mini-amp circuits, and also with an electret mic project.
    Sean in Michigan

  3. dfowler says

    Kersny,

    Nice instructable.

  4. dfowler says

    Daniel,

    Good idea.. I will look into this for the next board revision.

  5. kersny says

    Check out this instructable I made a while back, it is very similar to this: http://www.instructables.com/id/The-Radioshack%2c-Adjustable%2c-Breadboard-Power-Suppl/

  6. Daniel says

    May I suggest 3.3v 5v etc being available directly on the board, but with like a jumper that would allow easy selection. It would only require having space on board for 2-3 more resistors. A trimmer to adjust voltage requires a DVM and thats kind of annoying.

  7. dfowler says

    I hope you guys get some good use from the kits. I had a great time giving those away for typos.. I am so bad that I dont know if I can afford to keep doing that…

    I am doing a respin on the board and would welcome any comments or sugestions for improvements.

    The major change will be the addition of a set of pins that plug in like an IC would (0.3 centers) to allow for breadboards that have different spacing. I also hope to increase the size of pads to make it easier for inexperienced solders. One idea is to make the round pads oval and the square pads elongated rectangles. The idea is to make it easier to solder up.

  8. Chris says

    I just received *my* kit in the mail, and it looks great. Thanks, David!

    I hope to get it assembled tonight, though it’ll be a little while before I put it to serious use–my wife’s a teacher, and we’re heading out next week so she can enjoy her Spring Break.

    Now I just need a project to work on. Has anybody else experienced “hobbyist’s block”?

  9. Brandon says

    I received my kit a little while ago, but haven’t had any free time to play with it yet. Thank you, David, for sending me one. I’ll let you know how everything goes once I free up some time.

  10. Daniel says

    I am using NMEA sentences with mine. Im doing it in assembly though.

  11. dfowler says

    Eric,

    I am a GPS guy and have worked with NMEA for years and have had some experience SIRF chips as well. Are you planning to use NMEA or the binary format in your projects. From my perspective the question boils down to deciding if you want to support some other GPS in the future. Binarly formats are very easy to handle, you just need a set of C structures and some message sync management. NMEA is easy but requires string parsing and some care to handle all the posible issues.

    If you use Sirf binary, your code is easy but only works with Sirf. If you use NMEA the code is harder to do but the code will work with amost every GPS receiver.

    What are you planning?

  12. Eric says

    Hi Daniel,

    Right now it is something I pulled out of a surplus source. The chipsets are SIRF III and I have found that I can actually interface with it and toggle it between NMEA and SIRF Binary formats. Not bad for a 99 cent purchase 🙂 (Well, actually, it cost that to buy it, but it was like 10 bucks to ship. Still not complaining!)

  13. Daniel says

    Eric, what GPS module are you using? I’m currently working with a Etek EB-85a 5hz.

  14. Eric says

    Hi David, I received my kit the other day, and will be putting it together and using it for something very soon. It will be very useful to have it for power for a GPS project of mine sitting on the bench!

    -Eric

  15. dfowler says

    Daniel,

    The adjust pin is available on the breadboard so you can just remove the resistor and add the pot to your breadboard.

  16. Daniel says

    I am going to take out R2, and add a 1-5k ohm pot I have, im going to leave the R1 at 240. Ill actually have to think about it, and work it out when I have some free time before I actually do it, because I dont want a value out of the Voltage Regulators Range, Ive also thought about getting one of those 6 pin PICs and a 7 seg display, build me up a tiny DVM that will fit under it SO I can see the tuning voltage or something.

  17. Wayne says

    Hi all, mine works a treat, A big thanks to David for sending me one, I tested mine with all sorts voltages upto 30v and had no problems.I think there should be a pot of some sort on this so you are not tied to using the voltage you select during building

  18. Daniel says

    Everything is working on the board now, no problems.

  19. dfowler says

    Daniel,

    Dont glue a heatsink to it.. Lets figure out why it’s getting hot. Something is wrong. The bridge never got warm in my testing. I ran the module at 300mA for a day without a problem and with no heatsink.

  20. Daniel says

    I received it Thank you for the kit, Its been awhile since I soldered, so it was fun putting it together. When I use it in a project, ill send you the write up if you can use it.
    I just have to figure out why that Bridge gets so damned hot. Maybe ill glue a heat sink to it.

  21. Patrick says

    I received my “typo give-away” power supply today. Thanks so very much. I’m looking forward to assembling it and giving it a try as soon as some hobby time opens up.

    Now that I’ve discovered your site, I’ll be checking in now and then to see what’s new.

    I really appreciate the extra care and attention in your instructions and your explanations about why you did what. For those of us less experienced, but interested, this is a real gift.

  22. dfowler says

    Daniel,

    I am confused… Are you saying that the bridge is getting hot with no load applied? If you were loading it at 1.5A then the bridge may run hot but I dont see how you could get 1.5A when powered from a 650mA source. 1.5A is the max rating for the regulator but with a 650mA supply you should not get more then about 500mA. Really you should stay well away from the max ratings whenever you can.

  23. Daniel says

    I assembled mine and it works great, 5v 1.5amps, the wallwart im using is 9v 650mA, with an open voltage of 13-14volts. The Voltage regulator and the Bridge rectifier heat up, I know its normal for a voltage regulator to heat up, hence the heatsink, but the Bridge Rectifier gets scalding hot, Im sure on the upper tolerance of the device itself in the data sheet. Think its only getting hot because ive got no load? Or is anyone elses really hot? Not looking for it to melt down.

  24. follower says

    @desiredusername:

    Sorry, yeah, you’re right–I meant to say, put it in the 5V pin to bypass the regulator… (My excuse is I’m currently fighting a cold. :-D)

    –Phil.

  25. desiredusername says

    Hey, thanks for the info! I’ve been using USB or battery-wired-to-jack so far, but now I want to power a motor, so I need a high-current, external supply. FYI.

  26. dfowler says

    I will talk to the Curious Inveter about the 2 vrs 3V issue. 2 will work if you dont draw much current. If you want the supply to work at higher currents you will need a bit more voltage drop.

    If you are using AC input you will need a good bit more margin to prevent ripple. AC wall warts are basicaly just transformers wihtout regulators. Their output voltage can vary quite a bit with load. The one I tested said 9VAC at 350mA but when I loaded it at about 300mA it was outputting less then 8VAC.

  27. dfowler says

    The typical Arduino board has three ways to get power. From USB which is already regulated well enough, from a DC jack, which has a regulator, or from it’s 5V input pin which is not regulated. If you are using a DC jack or the USB to power the Arduino you would probably not need another 5V supply as you can get the power from the Arduino board already regulated.

  28. desiredusername says

    @follower:

    Are you sure? This is from the Arduino site: Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. A low dropout regulator provides improved energy efficiency.

    That sounds like Vin gets regulated.

    Love the site, though. I’ve thought about submitting an article, but I’m sure you all know more than me, so that’s probably pointless.

  29. follower says

    @desiredusername:

    Not that I would like to decrease David’s sales any 🙂 but the Arduino requires 5V *regulated* or ~7V *unregulated*–I assume the SparkFun supply is 5V regulated?

    If you use a regulated supply you would connect to Vin on the Arduino headers rather than the power jack.

    –Phil.

  30. desiredusername says

    I was this close to ordering the Sparkfun one when I noticed that a 5V output isn’t enough to run the Arduino, which requires a min of 6V and recommends 7V.

    This power supply looks perfect. I don’t suppose there’s any way to get SF to offer it for sale so I can combine shipping…

  31. follower says

    BTW the curious inventor page says “just make sure the input is about 2V greater than the output you want” but you say “Only concern is that your power source output at least 3V more then you want the module to output”.

    –Phil.

    P.S. Typo in that quote if someone wants it… 🙂

  32. Daniel says

    Yeah, I figured out what you meant after I posted earlier, about a Diode after the Regulator output. Just didn’t want to post again.

  33. dfowler says

    Daniel and Thomas,

    Thomas is correct. In some applications this diode is necessary to insure that the input voltage is always greater then the output voltage. I don’t think this is a concern on this power supply so I left it off.

    For the output voltage to be greater then the input the 330uF cap would have to discharge faster then the capacitance on the output side of the regulator. The bridge prevents it from discharging into the source so I believe its not possible to have the condition where the diode would be necessary.

    If the bridge were not there and this supply were tied to a power system such as in a car, it’s possible that the input capacitor could discharge back into the source causing the input to the regulator to be lower then the output. This is bad news for the regulator but I don’t think this circuit has a problem.

  34. Thomas says

    No, that is not what I am talking about. The 317 is sensitive to the output voltage being greater than the input voltage, which can happen under some circumstances, e.g when the input is turned off. This can force current into the output (and adjust pin). Something the 317 doesn’t like. This can be prevented with additional protection diodes.

    The datasheet specifies the conditions under which the diodes are needed. Something like when the output voltage is larger then 25V. In my experience it can happen with much lower output voltages, too. Therefore, I always add the protection diodes.

  35. Daniel says

    Thomas, current direction is maintained through the Full-Bridge I believe.

  36. Thomas says

    I am missing the typical diode connecting the 317’s output and input in forward direction. From own experience I know that the diode doesn’t have a purely decorative function 🙂

  37. dfowler says

    Jeff,
    I was not thinking of the switch as a protection function for the bridge. It is there to disconnect the power from the bread board.

    Another way to look at this is that the bridge substitutes for a bridge that would be found in a DC wall wart. There is no power switch there.

  38. dfowler says

    Berni,

    Yes, it would be best to have a trip on overload with some reset action to bring it back.

    Sparkfun has a module with a three position switch, off, 3.3, and 5.0V. I think this is very nice but I did not go this way. I was afraid that it was too easy to slip and switch to 5V when your circuit needed 3.3.

    This module does support just about any voltage, but you do have to select it when you put it together. The Curious Inventor site includes the resistors for several common voltage selections.

  39. Berni says

    I find the most safe limit the one that trips and needs a reset trough a button or something.

    Also had a idea to have the current and voltage adjustable trough a small DIP switch or something.

  40. Jeff says

    Hi,

    I like the project. I do have a question though. Why is the switch after the bridge and not before?

    Cheers, Jeff

  41. dfowler says

    Daniel,

    The comments about Kicad are spot on. I will look around for a tutorial. I do think there are some but I dont remember for sure.

    You might learn a lot by getting the free Eagle and doing one of the tutorials for it. Then you could come back to Kicad. But it would be a lot better to have a simple tutorial, maybe even a video to help people get started.

  42. dfowler says

    Daniel,

    This board is short circuit and overload protected. This feature is built into the LM317 regulator and I have tested it. You can short the supply without damage to the board.

  43. dfowler says

    Berni,

    I looked into adding a current limit and even a current indicator. I may do another version of this board with those features but wanted to keep this very simple.

  44. Daniel says

    Sorry, for a second post, but OctoPart… Great find!

  45. Daniel says

    I was just thinking about how I wanted to build one of these things, ive been drawing up some schematics. Sparkfun has one and its a nice design also. I think the only component that might have been helpful would have been a Current Protection Resettable PTC Fuse.

    http://www.sparkfun.com/commerce/product_info.php?products_id=8357

    And if you have some other scheme or contain one please ignore my tip. The idea behind the PTC would be that it would shutdown the circuit in the event of a current spike, by some sort of short in the powersupply and cut off current to 250mA or some other predefined current, so you do not damage any of your project components.

    Do you know of a guide for KiCad. Ive reading up alot lately on how to design my own PCBs but have no hands-on experience with eagle, or any other gerber software, Opening up KiCad with no direction ruined my day, haha I was hoping for some sort of tutorial. Maybe a future article on this design through KiCad, would make for some good reading.

  46. Berni says

    Good idea.

    I’m thinking of making one but with something like a current trip point, so it cuts off if the current goes too high.A good use for one of those 6 pin PICs. If i get to that il make a article.

    Phew… i got so many projects and no time.(AudioAmp, Oscilocope, Maze robot etc)