Variable Lab Power Supply

I do a lot of work with low voltage electronics which often require various voltages. I was getting sick of constantly set up a series of batteries and then selecting the appropriate resistor just to test a single small part of a circuit. Ideally, I wanted to be able to dial in to a voltage simply and quickly and test. So that is what I made, a variable lab power supply for testing electronics.

This variable power supply provides anywhere between 1V - 10.7V DC. It is really easy to make one slight adjustment to allow a range of AC voltages, but I never use AC, so I didn't bother. It is also really easy to provide 0V-36V, but I hardly ever need above 10V, so I left it with the smaller components that I had readily available.

There are several other lines available off of the var psu including: 12V, -12V, 5V, -5V, 3.3V, GND, Variable (1-10.7V), and a mains-outlet extension (115V AC). The mimimum current limit on any of the lines is 2 amps, the max limit is 20 A on one of the lines. I forget the exact limits on each particular line. These limits will be based on the power supply unit (PSU) you choose to use in this project.

To all the comments I am sure will ensue, yes, I could have used a PSU and just installed binding posts, but I rather liked the geometry of this box. The size was right if I some day want to mount it to the workbench (when I get a real workbench) and there was plenty of space to install the fancy bells and whistles that I wanted (namely, the panel meters and the switch along with the variable line).

Anyways, this is a fantastic addition to your electronics workbench setup!

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Step 1: Materials

Depending on how much spare parts and electronics you have around, you may already have everything you need. There aren't any unusual parts needed. With that said, here is the list of materials and tools:

8 binding posts ($0.18/each) Tayda - RadioShack
Volt meter ($7.95) Adafruit
Current meter ($9.95) Adafruit
Temp meter ($9.95) Adafruit
3-prong outlet
10K Linear Potentiometer ($0.50 - $0.95) Tayda - Adafruit - RadioShack ($3.19)
Knob for potentiometer ($0.19) Tayda
Switch (varies greatly)
- Cool Adafruit light-button on/off switch ($5.95)
- Personally, I like the look of the cheap one I got at Ax-Man's (surplus store, $0.50). I found the same switch for $2.98 at Menards
- RadioShack ($3.19)
Indicator LED (any LED will work) [optional]
- Tayda ($0.02)
- Mouser ($0.06)
PSU (computer power supply unit) one of the small ones will work, you should be able to find it for $5-25, easy.
- it is nice if you have a spare one around
- look near IT centers or electronics stores, they might have an old one for you
- search eBay, amazon, google for key words like "psu", "atx power supply", etc. (you dont need a full atx psu, look for the rectangular small ones, not the big square ones. Although they will work better if you want one)
- RadioShack supplies ATX PSU's if you want to go with one of the bigger ones.
Wire (multiple colors) I always prefer solid core ($2.50/25 ft.) Adafruit
Gorilla glue for mounting the front panel
Prototyping board
- ($2.49) RadioShack
- ($0.98) Tayda. Good quality, I love Tayda electronics.
LM317T ($0.23) Tayda - RadioShack
10 uF electrolytic capacitor ($0.01) Tayda - RadioShack
1 uF electrolytic capacitor ($0.02) Tayda - RadioShack
0.1 uF Ceramic capacitor ($0.01) Tayda - RadioShack
1N4001 Diode (x2) ($0.01) Tayda - RadioShack
220 ohm resistor (1/4 W) ($0.01) Tayda - RadioShack
Any spare LED's of your choosing (any color, any voltage, etc) Tayda has a concise, cheap collection (starting at 2 cents!). Otherwise, RadioShack caries a wide selection if you don't want to order online.
A fan or two to cool the unit (the size of the fan should fit the size of your case).
Solder + Soldering iron
Case (I am using an old NetGear box, it didn't work anymore so forget about how much value it is compared to the product) Just find any old box sitting around. Search behind computer repair center's for discarded anything.

I have included RadioShack as an alternative for buying parts online. It is definitely cheaper to order online (way cheaper). But Hey, if you want your parts pronto, there aren't too many stores around that offer these parts (except Fry's if you are lucky to live near one).