Left my power supply at work, so I had to build a new one
07/12/2010

I meant to bring home my power supply this weekend, but I forgot and left it at work. It was the motivation I finally needed to build a new one. I had been thinking about it for a long time, but since the old one still works, there wasn't any real reason to do it.

My old power supply is a modifed AT power supply. It was easier to work with because of the way the power switch was wired. In fact, after removing the huge bundle of cables, the hole was the perfect size for a switch from Radio Shack. But it was also the last AT supply I had, so if it ever died I wasn't going to easily make another. And if it ever died, I would have to go to a lot of trouble to make a new one. On the old one I opened it up and removed a lot of wires, drilled holes in the sheet metal case, and soldered in new jumpers to the binding posts. The other thing I didn't like was with the binding posts on top, I couldn't exactly stack things on top of it or fit it into a nice bench setup with easy access.

The new power supply uses an ATX power supply. An ATX supply doesn't turn itself on the same way, it's always in a sort of standby state and you have to short a lead to ground in order to get it on. Not quite as easy to modify, but not too hard either. I also wanted to leave all the wiring intact so that if it should ever die, or I ever wanted to upgrade it, I could swap it out.

The hardest thing about connecting to the power supply was finding the right connector. After lots and lots of googling, looking and crappy images on electronics sites, and looking at spec sheets from manufacturers, I found something which looked like it was the right connector. It fits perfectly with both a 20 pin and 24 pin ATX connector, but it's not quite right, the little clip on the side isn't in quite the right place. It works though since the friction of all the pins holds it together.

The ATX connector I used is a TYCO/AMP 2-1586000-4 which I got from Allied Electronics. The matching pins are TYCO/AMP 1586314-1, also from Allied. Since there is only one 12 volt pin on a 20 pin, and two on the 24 pin, I decided to also add two connections to the the 4 pin molex HD power connectors. I got the molex connectors from Jameco, part 42076, the pins are 42730.

Crimping the pins for the ATX connector makes a nice crunching sound, but you have to make sure to squeeze harder after the sound or else the pins fall off. I ran multiple light gauge leads together to a heavy gauge lead and used wire nuts to connect them. The heavy gauges have little lugs crimped onto them and are screwed down to the binding posts. No soldering involved at all.

For the box I used some scrap plywood. The front panel is made out of a piece of tempered hardboard. It is inserted into a groove around the front of the box so that later if I want to make some upgrades to it it will be very easy to replace. I already have one upgrade planned which is the green post, I am going to add a 7809 so that I can get 9 volts, something I kept missing on the old supply. For the 3.3 volt I wasn't able to find a 5-way binding post in orange (at least not for reasonable price) so for now I substituted a white one.

The ATX supply is held in at the back with a small piece of aluminum L-channel. The bottom of the case is removable and I drilled holes in it for ventilation. I still need to put some labels on the front, but over all I think it turned out very well.

You people bring matches for Mikey?
06/24/2010

I've seen lots of pages out there on making squibs or e-matches, but all of them used some method of making some chemical goop and then dipping your wires in it. I didn't want to mess with making goop, and I didn't want to mail order a bunch of chemicals that make the goop. So far this method that I'm using has worked very well for me, and the only "exotic" thing you need is the nichrome wire.

What I'm using is 22-24 gauge solid pair wire, little tiny gold tubes, regular paper matches, and nichrome wire. I happen to have rolls and rolls of the wire, but I'm sure pairs pulled out of cat5 cable would work well. The tubes are .081mm "beads" that I picked up from Michaels craft store. The matches just came from the grocery store. The nichrome wire was the only thing I had to get mail-order, and you can get that off eBay from lots of model rocketry clubs.

To make the squibs cut a length of wire about a meter long. (I made them shorter a couple times and all you end up doing is wasting time wire nutting longer leads onto them.) Cut one end staggered or offset by about half an inch and strip the ends.

Get a paper match and place it so that the longer wire sticks up above and behind the match and the shorter wire is in front of and below, then twist the match into the wires.

Thread two of the beads onto the nichrome wire while the nichrome is still on the spool. Wrap the end of the nichrome 3 or 4 times around the short wire in front of the match, then slide a bead down over the bare wire and crimp it in place. Then proceed to wrap the nichrome around the match head 3 or 4 times, then up to the other bare wire above the match and wrap that as well. Slide the other bead down, crimp it, and cut the nichrome to length.

If the matches don't feel like they're going to stay in place from being twisted into the wire, you can always wrap some tape around them to secure them.

I have been making my squibs this way for a couple of years and it has been extremely reliable for me for setting off my fireworks from my iPhone. It's very cool to be able to sit in the audience and watch the fireworks show from their perspective.