Here is an easy way to make your own bench power supply that provides 5v, 12v and adjustable for 1.2v to 11.6v! If you don't have the resources to make one but want it, I sell them on my Etsy store - see bottom of the instructable for link and a video demo. I appreciate your support!

Step 1: Introduction

For as long as I have been involved with Arduino and Raspberry Pi development, I have always been happy with fixed power supplies. The only downfall was switching power cords if i wanted 5v then 12v. Recently though I begin to find uses for other voltages. If you use motors or low voltage applications, I bet you can find some regular use for a bench power supply that you can use 5v or 12v with the flip of a switch or have instant access to any voltage from 1.2 - 11.6 without the hassle. For this instructable I will show you how to make your own variable power supply - or you can just buy one from my Etsy Store. Links for my store and a YouTube video demo of this unit are at the bottom of this instructable.

Step 2: Supplies

Everything you need you can get from amazon, eBay or a local electronics store.

You will Need:
(2) 3 terminal power distribution blocks - I made 1 of mine with a PCB and terminals

Bunch of M2 risers and screws for securing and support

Some heat shrink

Terminal connectors

3 way switch (6 prong)

10K POT

LM2596 Step Down (Buck Converter)

(2) Banana plug inserts

Banana cable

(2) digital volt meter displays (not shown)

Dual voltage power cable (5 and 12v - usually on a 4 pin molex conn for disc drives)

Red, Black, Yellow and Green wire

casing of some sort or design

Step 3: Preparation and Case

So, get your supplies and sketch out what you want the front panel to look like. I wanted my panel to include (2) voltage meters (one for the fixed power and one for the variable), each with its own Banana cable inserts, a POT knob and a power switch. Next I will be adding USB ports, but let’s not get too far ahead. Next you need a base, so layout the power blocks and the buck, add at least 1 inch on all 4 sides - and that it is at least as wide as the front panel. Now you’re ready to get started.

Modify the Buck converter

Next thing we need to do is to modify our buck so we can actually use it for something. Those ridiculously small screw adjusters just won’t do! The default POT is that blue box on the edge of the buck. Desolder it and put it off to the side (or trash). Then using enough wire to reach the panel from where you placed it, add an extra 1-2 inches and cut a red, green and black set for the 10K POT. Solder the ends to the newly 3 vacant holes on the buck (power, read, grd) and to the 10K POT (power, read, grd).

Build a power distribution block

I decided to make my power distribution block so it will do just what I want it to. I included an extra set of terminals to power a 5 wire ammeter (amps and volt meter in one) as an option. In the picture above you can see the distribution block, 1 terminal on top and 3 below. For ease of use, make the left side of each the ground and the right power. From the single terminal solder a jumper to the 2 terminals on the right - do not wire to the terminal on the left which will go to the variable power display (on mine it is to the left looking from behind), each getting 1 red and 1 black wire. You also need a set of wires to go to the INPUT on the buck - so 3 of each out of the main terminal. There is a finished picture later for more reference and a crayon looking diagram just below. For the terminal on the left, solder a red and black wire to the block that will be long enough (plus your 1-2 inches) to reach the OUTPUT of the buck.

Step 4: Assembly

Now you can begin your assembly of the unit. Following is my order of work, if you are more comfortable with another order, go for it, just make sure you use all of your parts!

Front panel - mark out the positions of the voltmeters, POT, switch and plugs on your front panel and drill and cut away. handy tip for some: I made my panel with (2) 1.5” strips and then glued small risers at the measured intervals of the displays and switch, that gave me the sized, square windows you see in the picture. You also see the small wooden strip to accommodate the displays as they are slightly shorter than the switch. When done, slap some paint on it and put it aside for now.

Base - Attach the primary power block, buck and distribution power block using your M2 risers and screws. If you are going to use a metal or conductive casing you might want to use some insulating fiber spacers. Maybe more than than might.

Displays - Cut (2) red and (2) black (not the display wires!) wires long enough to reach from the banana plug lugs (the rear) to the distribution block (terminals 1 and 3), add .5”-1” to the length to be sure. Each display has 2 wires, red and black. Solder one of the display red wires and 1 cut red wire to a connector to attach to the banana lug. Repeat for the black wire, then repeat for the second display.

Power -

Switch - On your 3 way switch, solder and heat shrink wrap 3 sets of power wires. The top and bottom sets will go to the main power block and the middle (2) wires to the input on the distribution block. Measure them and cut .5 - 1” longer and attach. To be more specific, the top set will go to terminal post 1 (12v) and terminal post 2 (grd). The bottom set will go to terminal post 3 (5v) and terminal post 2 (grd). I used yellow wire for my 12v just to distinguish it from the 5v. The middle set will go to the power distribution block beneath the displays (the one on the side by itself). Do NOT attach the wires to the blocks yet, that comes soon. *Note: when using the switch, when you depress the toggle down it connects the voltage wired to the top posts and depressing up connects the bottom voltage.

External Power Cable - Following the same pattern, you can attach your variable voltage power cable to the main power block. Cut off the molex connector and you should have 4 wires, red (5v), yellow(12v) and a pair of black(grd). Attach the yellow (12v) to terminal post 1, black wires (grd) to terminal 2, and red (5v) to terminal 3. plug the cable in and use your voltmeter to check that everything matches. While optional, I prefer to solder connectors to the power cable ends to help secure them in the block.

Power Distribution Block - you should have already used jumpers to connect the primary “in” terminal to 2 of the distribution terminals and have a longer wire set for the buck. The terminal on the left runs to the OUTPUT on the buck. From the left terminal, run the red power wire to the (+)OUT and the black wire to the (-)OUT on the buck and solder. From the input terminal you have a longer set of red and black wires, these are soldered to the INPUT (+) and (-) on the buck.

Step 5: Final Steps

Panel - First you need to assemble the front panel. Now that the paint and glue are dry, begin the deployment of your parts!

Insert the switch first. Thread the wires through and attach them to the main power block and distribution block per your configuration. Next, insert the POT into its slot and secure to the front with the mount screw. Attach the banana cable connectors with the screws attached but loose. Insert the displays and secure the connectors to the banana plug lugs, check that you attach the power and the grounds to the correct lug. Tighten the lugs snugly. Now attach the cut wire from the connector to terminals 1 and 3, checking power and ground matches for each.

Make sure everything is secured and then do final attachment of the panel to the base and sides if you have them!

Plug in some banana cables and flip the power switch! You should see your displays light up and ready to provide some power for that next project!

If you want to see a video demonstration see my YouTube video for this project: