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Variable DC Power Supply

While my DIY fixed voltage power supply has been a mainstay on my workbench, its options of 3.3v, 5v and 12v have been a little lacking as of late. It's time to make a variable voltage supply to provide more power options for my projects. This solution is capable of providing 1.2v to 14v and is easily upgradeable to around 30v if need be.

The device simply takes DC power from a wall wart and reduces it to the users desired voltage. The most practical options involve using either an LM317 linear regulator or a buck (step-down) converter. I ended up using a buck converter as I already had a few of them, they're more efficient as they're a switch-mode power supply and you don't need to go through the hassle of adding the supporting components and building the step-down circuit like you would with the LM317. You just need to extend the adjustment potentiometer, install a voltmeter to read the output voltage and add connectors to interface with the devices you want to power.

The essentials of this project include the DC voltmeter, buck converter, 10K linear potentiometer and a DC power supply. I found a 15V 1.5A wall wart amongst my collection that's adequate to supply the juice I require. If I need a higher voltage for a project, I can hunt down a supply of up to 30v to increase the supplies range (buck converter's max is 35v input). My current fixed voltage supply uses alligator clips that attach with RCA plugs and I wanted to do the same with this unit. In addition to a set of spring clip audio terminals there's two female RCA connectors mounted on the side.

As I'll need access to the potentiometer while the converter's tucked safely in it's case, it will need to be extended. The original pot is desoldered and the new one attached with some ribbon cable in its place.

I gave the parts a quick measure and determined a layout where everything would fit. Had to drop the power switch due to space concerns but it'll work just fine without and it's already a fairly snug fit. 

The slot for the voltmeter was cut with a dremel and the holes marked with a punch and drilled out.

After a quick scuff with sandpaper and a few coats of metal friendly paint inside and out, she's beginning to look the part.

The original plastic mounts on some of the connectors are no longer needed and will just take up space so I trimmed them down with a dremel and attached wires.

I installed the voltmeter, spring clip terminals, RCA connectors and power jack into the case with a small dob of hot glue where necessary for a light hold until I can confirm the build is functional.

The wiring is fairly simple. The power jack is connected to the power supply for the voltmeter and the input of the buck converter. The output is connected to the RCA jacks, spring terminals and the sense wire of the voltmeter.

Now that everything's confirmed working, anything not held with a nut got a good douse of hot glue to secure it in place.

Everything appears to work fine. I powered up some motors and fans then blew up an LED or two. Good times.