Breadboard Power Supply Adaptor

The Challenge

One consistent challenge that I face in my lab is how to power breadboard projects. I use breadboards to prototype almost all of my designs and I’ve always had less than ideal setups.  Between my bench power supply, which has banana plugs, and the many wall transformer power supplies I have around the house with 2.1 mm plugs, I just do not have any options that are breadboard friendly.

To illustrate my dilemma, in the past, I end up with solutions something like these photos below (not the easiest or prettiest of ways to connect to the breadboard):


9 volt transformer supply with 2.1mm plug


Bench power supply connected with alligator clips and jumpers



It does not take more than a casual glance at the pictures above to recognize that while functional, these are not ideal solutions. In both cases, the connections are too easy to accidentally dislodge and there is a risk of a short with the second one.  There had to be a better way.


The Better Way

Before a design could be had, it needed some requirements.  As I pondered the requirements, I came up with the following technical specifications for this little device.  I wanted to be able to optionally use my bench power supply or wall transformer and that each would have a secure connection to the breadboard.  I also wanted the ability to switch it on or off and have the option to power either both rails or just one with the external supply.

As I worked through the design, it became a simple but effective solution.  To start, I created a project in Eagle CAD around the connectors I needed, and designed the board shape to match up to the standard 830 point breadboards that I use in my lab.  There were a handful of other features I wanted to include such as an optional filter cap, an on/off switch, and a power status LED.   As I got designing, I decided to refine a few of the features.  Many of my projects have more than one input voltage.  To facilitate this, I added a jumper block to connect or disconnect the second power rail for projects that need a dual voltage.


Schematic Capture and Component Selection

With the basic design framework laid out, I started researching the components needed.  I personally tend to use the online Mouser catalog to help me sort through the vast quantities of components available.  I stuck with all through-hole components to make this project easier to assemble at home.  With all the parts identified, I returned to my project in Eagle CAD and found each of the components in my component libraries.  I connected them electrically as shown in the schematic below, and double-checked the design (an often under rated step in the design process).


Schematic captured in Eagle CAD


Board Layout

With the schematic complete, it was time to move on to the board layout. Breadboards use a standard 0.1 inch pin spacing, but when I measured the spacing between the power busses, I noticed that they were slightly different.  After some trial and error, I realized that the actual spacing between the power bus pins was 1.85 inches O.C.  With the header pins placed at this location, the board outline was adjusted to create a proper fit.  After arranging the components, I added a ground pour to the top layer to simplify routing.  The Eagle autorouter made quick work of the rest of trace routing and the resulting board design looks like this:


Top view of the board layout and its relevant dimensions


Board Assembly and Testing

I ordered a batch of these boards from my favorite purple PCB vendor (OSHPark) online and assembled them.  I couldn’t be happier with the finished product.  The fit is perfect and they snap into the power bus tightly and stay put.  This little device has gone through extensive testing as I have been using these on all of my breadboard projects ever since I got the first one assembled.  They really work wonderfully!


Assembled board powering a test circuit


Assembled board closeup


Building your Own

If you would like to build one or more of these for your own lab, the design is a fully open source hardware project with no restrictions on reuse.  Below you will find the bill of materials, along with a link to a shared Mouser project.  The other links take you to OSHPark to be able to purchase the shared PCB, or if you rather, you can go to the GitHub link and download the Eagle BRD and SCH files.

I hope you find this project as useful as I have, and if you have any suggestions for other projects you would like to see, leave me a note in the comments.


Bill of Materials:

Mfr. # Manufacturer Description Order Qty.
571-0100 Deltron Test Sockets SINGLE PCB SOCK BLK 1
571-0500 Deltron Test Sockets SINGLE PCB SOCK RED 1
163-7620E-E Kobiconn DC Power Connectors PCB 2.1MM 1
PVA1EEH1 C&K Components Pushbutton Switches DPST MOM LNG ACT 1
MF1/2DC1501F KOA Speer Metal Film Resistors – Through Hole 1.5K 1% 100PPM 1
WP710A10SGD Kingbright Standard LEDs – Through Hole Grn 40mcd 568nm 40 deg Diffused 1
67997-472HLF FCI / Amphenol Headers & Wire Housings 72P HDR 1
M7581-05 Harwin Headers & Wire Housings JUMPER SOCKET OPEN TOP RED 1
ECA-1HM100I Panasonic Aluminum Electrolytic Capacitors – Leaded 10UF 50V ELECT M RADIAL 1


Link to shared Mouser project:

Link to shared OSHPark project:

Link to sch and brd files:

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