Thrifty Tinkering

Repurposing discarded power supplies

Johnny "Meccano"

Issue 59, June 2022

Johnny shows us how he repurposed a salvaged power supply to power his projects.

Being thrifty is a great trait for a maker. Repurposing components and avoiding the need to purchase new parts, not only saves you money and time, but it’s a bit of a thrill. It’s why we makers avoid throwing things out, right?

Our regular contributor, Johnny, has been able to repurpose an old discarded power supply to power his Arduino projects and wanted to share. Here's what Johnny had to say about his project.

Op Shops usually have a big box of discarded plug packs and I’m always ratting through them looking for 12V with 1A or more. Sometimes I’ll find a laptop power supply. These are very good quality switchmode power supplies that are usually 12V, 3A and sometimes even 5A. That’s a whopping amount of power for your maker projects!

Repurposing these power supplies is good for your pocket, good for your brain and good for the environment. Some Op Shops stick to the letter of the law and get them tagged and tested which brings the price up but most just throw them all in a big plastic tub with all the RCA cables and old phone leads with a price tag of $1.00.

Just recently, I was browsing the Op Shops around Bright and Myrtleford when I came across this power supply with a mysterious looking mini DIN plug on the end.

If you look closely at the label, you can see a picture of the plug pinouts. The 5V and 12V caught my eye because a lot of my projects require 5V for the Arduino and 12V for the motors.

A Google search for the part number SW34-1202A02 revealed lots of sites offering it for sale but the description was nothing more than "AC/DC Power Adapter compatible with SINCHO SW34-1202A02 for many external HDD enclosures".

After snipping off the plug, I confirmed that black was Ground, green was +5V and white was +12V with my trusty little true RMS meter from Altronics (Q1135).

Next, I cut off a strip of Vero board with 5 rows of copper tracks. 2 rows on the left for 5V, 1 row for a gap and 2 rows on the right for 12V. Then I soldered the black Earth wire to row 1, green 5V to row 2, white 12V to row 5 then a jumper from 1 to 4 for the Earth. Row 3 isn’t used. It’s just to space out the header pins. I put 3 double header pins on the 5V rows and another 3 on the 12V rows.

Now it was just a matter of gluing it down to the case beside the green power indicator light with 5-minute Araldite. I also blobbed a bit onto the cable just to keep the strain off the wires.

The labels were made on a Dymo label machine making sure the – and + indicated the polarity. You could also use keyed header pins to prevent accidental reversal of polarity but I wanted the versatility of choosing polarity myself.

Johnny "Meccano"

16 year old student and Meccano builder