DIY DC Power Strip

Ever need power and need it fast? Would you rather not breadboard a power supply when your creative juices are flowing or just want to have a lot available? I haven’t really…but I expect to in the future when I finally have some more time to myself…so I built the one and only DC Power Supply! As far as I can tell, nothing like it exists. Multi-output bench supplies are expensive and “DC Power Strips” all seem to be one voltage…and if you’re working in digital electronics like I do, +15V isn’t really that useful.

Behold, the DC Power Strip!

Schematic

Here’s the short version: I created this by gutting out a $7 power strip from Wal-Mart. A carefully selected DC power supply was fitted into the left portion of the power strip to get me +15VDC from +120VAC. The voltage outputs, as shown in the picture, are +15 (straight from the DC supply), +10, +5, +3.3, then two adjustables from +1.25 to about +13. Each of these is connected to a SPDT power switch threaded straight into the gnd plug on the adapter. LEDs serve as indicators when a certain voltage is active. Each output voltage has a stranded wire with a pin header soldered to the end for easy connection to a breadboard. It turned out very nicely.

Want to learn how to make one yourself? Here’s what to do:

Supplies:

• Power strip
• (x6) SPDT switche (I used mini guitar toggle switches with a thread diameter of around 6.5mm or so)
• (x6) LED
• (x2) 1k pots (Keep them as small as possible, I used the 392JB1K)
• (x2) Dial of your choice to go on top of the pots
• A bunch of header pins
• A good length of stranded wire
• (x3) LM2937 (+10, +5, and +3.3 versions – one of each)
• (x2) LM317
• (x5) Heatsinks for your regulators
• Resistors – 1/2 Watt: (x3) 750 ohm, 510 ohm
• Resistors – 1/4 Watt: 240 ohm, 160 ohm, (x2) 110 ohm
• Capacitors: (x5) .1 uF, (x5) 10 uF
• 15 V DC Power Adapter (I used the EPS150080UPS-P5P-KH)
• Other connecting wire
• Hot glue gun/glue
• Semi-opaque paper
• *You may need other supplies – I’ve tried to cover them all but could have missed some

Tools:

• Dremel/Cutting Bit
• Soldering Iron/Solder
• Wire strippers
• Wire cutters

Safety:

• Safety glasses
• Protective gloves

SAFETY NOTE: You will be dismantling a power strip and likely be plugging it in while it is open so you can test your circuit. This is very dangerous and can cause death or serious injury. Take every precaution when handling the live nodes and ideally do not leave them in the open when live at all. Also, don’t cross the wires…the Ghostbusters may be able to get away with it, but real people can’t – I only tripped the breaker once…

Step 1: Plan

Yes, plan what you want to do. It’s unlikely you will do it the exact same way I did…and you probably don’t want to either . Learn from my mistakes! Make some sketches and get an idea of what specifications you need. Do you want to do digital logic only or do you want to do crazy op-amp stuff with negative voltages?

Step 2: Gather Some Supplies

The first thing you need to do is pick up a power strip and a DC power supply. You probably want a larger power strip made of plastic to make things easiest. Mine was made of ABS plastic, which is very soft. You may choose a metal strip, but be prepared to be extra careful…although you could make a VERY nice one enclosed in metal if you do it right. Once you get the power strip, carefully pry it open. Mine didn’t have any screws and so it just took a bit of patience. Make some careful measurements and search for a DC power supply that will fit inside. Don’t plan on having a lot of extra room when you take the casing off your power supply – they don’t build them with a lot of space to spare. My choice adapter was roughty 45×61 mm.

Open Power Strip – notice all the plastic inside that will need to be removed later on.

DC Power Supply – roughly 45×61 mm.

Step 3: Get the Rest of Your Stuff (& breadboard)

If you have a power supply that fits in your power strip, then you’re set to go. Go ahead and order the rest of your parts, then breadboard them. You want to actually be sure your circuit works before you spend all that time putting it together.

Not lying – I breadboarded mine! I’m glad I did, too, because I had problems…Note that the LM317 pinout is DIFFERENT than the LM2937.

Step 4: Dremel Out the Inside of the Power Strip

In order for all of the electronics to fit, you’re going to have to dremel the extra plastic out. I used a simple cutting bit (it was actually a bit too large) and did my best to cut things away. The soft ABS tended to melt and smell, but it wasn’t terrible if I worked quickly. IMPORTANT: Always wear proper safety gear including safety glasses and protective gloves. A dremel is a dangerous tool. I recommend putting the power strip in a vice if possible before cutting so you can control the dremel with two hands.

Partially dremeled out power strip. Oh yeah, it produces a lot of dust, too.

Step 5: Solder Everything Together

At this point it’s really all about putting the electronics in. Technique here is sort of up to you, but I’ll share a few tips.

While it would be a whole lot easier to remove the bulky power cord while you’re working, you probably want to test your work as you go. Try to secure the power strip so it doesn’t move while you work.

As mentioned: test as you go. Finding problems early is key!

I used some nice semi-opaque paper over one of the “eyeholes” on each of the 6 power strip outputs to diffuse the LED. I also placed the LEDs in parallel (physically, not electronically…although both are true) to get a unique “square” light source. (See image below)

If you get the right type of toggle switches they will actually thread nearly perfectly into the ground holes. Mine fit perfectly with no additional support and they are quite sturdy.

Use protoboard if you like. I opted to use air…which was kind of difficult, but it worked out OK. Everything is basically floating around and my power strip is sort of a mishmash of wires soldered together. It worked out OK for me, but you may want to solder a bunch of “units” together. That would actually probably be better…

Before you start putting all the stuff in, figure out where you want your pots to stick out and dremel or drill out some holes for them. This is a lot harder when everything is already together, trust me.

When you run your output wires, use some nice stranded wires. If it’s thin enough that it slides around easily, tie a knot in the end so you don’t pull on your solder joint. I used some coaxial RCA cables I had lying around. I don’t really need coaxial , so  Just used one of the layers. It’s thick, sturdy, and worked quite well. I soldered some pin headers onto the end and secured it with some electrical tape for good measure. This way I can plug them into a breadboard very easily.

The switches fit very nicely into the ground pins. Also note the semi-opaque paper strips I cut out and taped into the power strip. The LEDs are hot glued into position.

Here’s a relatively useless blurry picture of how things looked inside for me. When I got done I was a little excited and forgot to take good pictures, so this is all I have. It looks a bit messy, but it is secure and structured quite well.

Notice the diffused paper and unique LED look. It’s sort of classy…

Well, that’s it! This is my second DIY project. You may be interested in reading about my

DIY Light-Up Picture Frame

Feel free to leave me a comment if you have any questions, suggestions, critique, etc! Thanks!

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Here Lies Trac Phone

So I decided to add myself to an existing Verizon plan today – it’ll cost me $10/month, which is way cheaper than getting my own plan of any kind. I’ll be getting a brand new phone in the mail (of the free variety) and can finaly enjoy the features of a non pay as you go plan. I’ll be ditching my Trac Phone as soon as the minutes are gone.

Why am I glad? Because my Trac Phone is 3.5 years old, tends to freeze, has the battery life of a grape (well, maybe an onion), has a taped together case, gets terrible reception (despite already using the verizon network), has a low resolution screen, and probably more. It has served me well, though, and I would have been “happy” to keep it for another year.

Granted, it is in pretty good condition. I’ve always kept it in the case and the only scratches are on the corners where I’ve dropped it…

Trac Phone - Top View. See the tape holding the case together at the bottom?

Trac Phone - Side View

Make: Technology on Your Time

I thought I’d just highlight my favorite website/blog – frequent features of various DIY and other electronic or similar projects found on the web or submitted. It’s sort of the Lifehacker for the hardware-inclined.

I usually check the Blog a couple quick times a day: http://blog.makezine.com/

There is a ton of content and it is updated often. They even have a store with several neat little gadgets and such. Check it out!

Christmas Light Show

Here’s a video of a Christmas light show myself and another guy did as part of an undergraduate course. The actual hardware was already created for us, so we didn’t have to worry about the high voltage switching and all that. Our job was to write a program in MASM to write out through a parallel port to control the switches.

This video is a little overboard for what the lab required, but we thought why not do something really neat with this since we have it in front of us. See the video below, or read some more details about how it works below the video.

Like I said, the program was written in MASM. That’s the Microsoft Assembly Language. This worked OK, but MASM isn’t ideal for this sort of project. Since we ran this program on a Windows machine, there are a lot of timing issues. If you watch the video a couple times you’ll pick up on some of them. Windows is an interrupt-based operating system, so our program wasn’t guaranteed to run like we wanted it. In the end we had to run it with realtime priority in Windows XP to get any sort of reasonable result.

The program was written as one giant data table. Here’s an example of that code:

                BYTE    01110111b, 01110111b, 11100111b,  MAIN_EIGHTH    ; Da, da, da, da, da, da, daaa (second time) (start in center and go out to bottom bars then back in) [Q]
                BYTE    01110111b, 01110111b, 11100111b,  MAIN_EIGHTH + MAIN_ADJUST_A   ; |
                BYTE    11111111b, 11111111b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11111111b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11111111b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11111111b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11111111b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11111111b, 11101111b,  MAIN_EIGHTH    ; |

                BYTE    11111111b, 11101110b, 11101111b,  MAIN_EIGHTH    ; | [QLP]
                BYTE    11111111b, 11101110b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11101110b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11101110b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    01110111b, 01100110b, 11100111b,  MAIN_EIGHTH    ; | Dum dum
                BYTE    01110111b, 01100110b, 11100111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11101110b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11101110b, 11101111b,  MAIN_EIGHTH    ; | 

                BYTE    01110111b, 01000100b, 11100111b,  MAIN_EIGHTH    ; | [QLPKO]
                BYTE    01110111b, 01000100b, 11100111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11001100b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11001100b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11001100b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11001100b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11001100b, 11101111b,  MAIN_EIGHTH    ; |
                BYTE    11111111b, 11001100b, 11101111b,  MAIN_EIGHTH    ; |

The three bytes at the beginning are data bytes that control the lights. The most significant three bits of the third byte are unused. The last byte, seen as MAIN_EIGHTH above, is a delay. We have several constants defined that define delay in milliseconds. MAIN_EIGHTH represents 1/8 of a beat in the primary portion of the song. We used quarter notes and sixteenth notes here and there too. The MAIN_ADJUST_A is a small adjust to help synchronize things. This segment is fairly clean, but other segments have tons of adjustments made to them. Ideally, this program should have been written on an embedded system, but that wasn’t part of the project.

To execute the program, there is a while loop that shifts the first three bytes out serially, then calls a delay routine. In the end, you get pretty good results.