Sunday, August 30, 2009

A little info...

...on the controller I'm going to build.

Like I said before, I plan to control all the elements of my haunt with Brookshire software's Visual Show Automation (VSA) software. VSA's a pretty amazing piece of software, able to control all sorts of hardware interfaces. One of those interfaces is a parallel port relay board, more commonly known as a kit 74. I plan to build a version of this controller, (2 of them in one enclosure, actually) with one slight modification.

Hauntforum member Monkeybasic has written a really cool add on for VSA called Helmsman. Helmsman lets you create playlists of VSA routines and .mp3 or .wav files, control the volume of each routine or sound file individually, control the relays of a kit 74, and most importantly for my application, provides external triggers through the parallel port. And best of all, it's free! My relay controller will have terminals exposed for the triggers. If you don't have a need for the triggers, I'd recommend saving yourself the headache and just buy the kit 74. I'm building mine because I have most of the parts on hand, and I'm a glutton for punishment.

The way the parallel port relay board works is really pretty simple. Pins 2 - 9 of the port are the data pins, D-0 to D-9. When VSA tells relay 1 to turn on, what it's really doing is telling the computer to send 5 volts to pin 2 of the parallel port. So all we have to do is use that 5 volts to trigger a relay. Simple, right? Well, almost. The parallel port can't provide enough current to trigger a relay and it's pretty sensitive to power spikes and shorts, so we need to give it a little protection.

To do this, we'll use a transistor. Transistors are cool. (I think I'll have that printed on a t-shirt - I'm proud of my geekiness.) A transistor works like a switch. When you apply a small amount of current to one pin, it allows a larger amount of current to pass between the other two pins.

The transistor I'll use is a 2n-2222 switching transistor. You can pick up a pack of 15 at Radio Schmuck for less than $3. The pin configuration is shown above. The middle pin is called the base. When you apply 5 volts from the parallel port to the base, it allows enough current to flow from the top pin (called the collector) to the bottom pin (the emitter) to trigger the relay.

Just to be on the safe side, I'll place a 1k resistor between the parallel port and the base of the transistor, to limit the current flow to the transistor and help protect the parallel port.

With the transistor handling the current, I can add in the relay. The relay is just a switch that uses an electromagnet to turn it on and a spring to turn it off. When you apply power to the coil of the relay - in my case 12 volts - it triggers the relay. So it's just a matter of connecting one side of the coil to a 12 volt power source, the other side of the coil to the collector of the transistor, and the emitter of the transistor to ground.

Sounds simple enough, and it would work if I stopped right there. But there's one more area that could potentially cause a problem, and it's not at all obvious. Put your propeller beanie on, cause this is gonna get a little geeky. When you pass an electrical current through a coil of wire a magnetic field is generated. That's how the relay works - the current turns the coil in the relay into an electromagnet which in turn pulls the contacts closed. But - here's the part that's not obvious - when the current is removed from the coil, the magnetic field collapses and creates a spike in voltage. This spike can be as much as 200 volts, which would wreak havoc on our poor transistors and computer port. So, I'll need to give that nasty energy spike some place to go. I'll do that with a diode.

A diode is a nifty little piece of hardware that kind of acts like a one way valve for electrical current. What I'll do is place a diode across the coil of the relay in such a way that it won't interfere with the normal operation of the relay, but will give the spike (called back EMF) a place to go once the parallel port tells the transistor to stop passing current.

That pretty much covers the basics. Just build, rinse, repeat. I'll get some pics of the actual build as soon as I actually build it.

Sunday, August 23, 2009

Thursday, August 20, 2009

haunt juice

In years past I've strung extension cords all over my lawn, stuck flood light holders all over the place, and filled power strips with wall warts and X10 controllers to power my Halloween props and lights. It got the job done (mostly), but it was a mess and potentially a fire hazard. Since all my existing props run on either 12 volts or 5 volts already, the decision to move to low voltage lighting is a simple one. I've already started making small spot lights, so it's time to focus on powering and controlling them.

My plan is to power the lights and a few small props with a modified computer power supply, and control it all with a couple of homemade "Kit74" type parallel port relay controllers and Brookshire's VSA software.

Here's my victim - a cheap generic ATX PC power supply. You can buy these new online for just a few dollars, or if you have an old junk PC laying around you could scavenge the power supply from it before you send it to the recyclers.

This one says it's rated at 300 watts. I suspect that's 300 watts ILS - if lightning strikes.

An ATX power supply puts out +3.3 volts DC, + and - 5 volts DC, and + and - 12 volts DC. The main connector has either 20 or 24 pins, and contains all the power leads as well as leads for status and turn-on. There are also power leads in all the smaller connectors on the supply.

The color of the wires denotes the voltage: yellow is +12 volts, red is +5 volts, orange is +3.3 volts, black is ground, blue is -12 volts, and white is -5 volts.
Grounding the green wire turns the supply on. The gray (or sometimes brown) wire is the PC's status lead. The only wires we're concerned with are the positive voltage leads, the ground, and the turn on lead.

PLEASE NOTE: ELECTRICITY IS DANGEROUS! Be extremely careful when working on this or any other project that uses electricity, particularly mains voltage! I'm not responsible for any harm caused by attempting this project! If you're gonna do this, do yourself a favor and short across one of the red leads and one of the black leads before you start cutting wires or open up the case of the power supply. And it should go without saying - make sure it's unplugged!

Here I've cut off all the connectors leaving as much length as possible outside the housing of the power supply, and cut away all but the green wire, four of the black wires, and three each of the orange, red, and yellow wires. (The number of leads is arbitrary - just make sure you have at least one of each.) I'll connect a switch between the green wire and any one of the black (ground) wires. I bought this switch from Radio Shack, (excuse me, I mean The Shack.) Not sure what part number it is, but any SPST switch rated for 120 volts should do.

Here I've drilled a hole in the top of the supply's housing and fed the green and black wires through to connect to the switch. Be careful to make sure you have room inside the supply's housing for the switch, and that the wires don't make contact with anything.

Oh, and if your switch is held in place by a nut on the back side, don't do what I did and forget to put the nut over the wires before you solder the wires on the switch. I guess I must have been in the mood to do it over.

For safety's sake, you really should have a constant load on your supply so that the capacitors drain when it's shut off without a load. A 10 ohm 10 watt sand cast resistor between one of the 5 volt (red) leads and a ground (black) lead will ensure that the caps drain and there won't be any unwanted shocks or surprises when you hook the supply up. I didn't have one on hand here, but I left a red and a black lead available so I can add one. (Just need to make another run to the love Shack.)

Here's my almost finished product waiting to be added to my yet-to-be-built controller board.

And just because I have to show it in action, here it is powering a 12 volt bulb.

Next time - the controller.

Friday, August 14, 2009


Mr owl patiently waiting to have his head reattached, poor fella. He's got the wire spool monster lookin out for him, though.

Thursday, August 13, 2009

LED spots

UPDATE 9-24-2015 - It appears that the cpvc parts I originally used are becoming hard to find in the big box stores. Home Depot's website shows everything but the elbow in stock at my local store, but I haven't verified it. But *I think* Amazon has everything available. !!!MEGA HUGE DISCLAIMER!!! - I haven't ordered these parts myself - I'm just going by the description - so if you order them and they're wrong, just remember that Amazon has an awesome return policy.
Pipe - this is for 10 2 foot lengths, enough for 20 lights.
Electronics Goldmine has some of the ultra bright LEDs that Otaku originally posted about. These are white, not the blue ones I used, but they are BRIGHT.
I've also had quite a few questions about power and wiring for LEDs. I've usually used modified computer power supplies (see here and here), but it is possible to use batteries, cell phone chargers, or old discarded wall warts (as long as they're D.C.). How to wire a particular combination of LEDs and power supply or batteries is going to be different in almost every case, but I've tried to explain how to figure that out here and here.
And finally I'd like to thank everyone for the kind comments about these - I never imagined I'd have this much interest!

(Edit: Since this was originally posted some time ago and the LEDs I used are long gone, I thought I'd point everyone to Lighthouse LEDs as a source for LEDs. I've never used their stuff, but I've heard from quite a few people who have & they come highly recommended.)

(Edit again: Thanks to Aaron Bolton for pointing out that the fittings used here are actually cpvc. My local Lowes no longer carries the parts, but they are available on their website. The Home Depot stores near me do still carry them, & they're available on the Home Depot website as well.)

A few months back, Otaku over at posted a link to some ultra bright blue LEDs at Electronic Goldmine. On a whim I ordered a few of them, not really knowing what I'd do with them. Well the other day I was perusing the isles at Home Depot & happened down the PVC isle. I noticed a few small fittings & it struck me - spot lights! (Cue dramatic music)

So without further ado, I present my cheap, small, easy low voltage spotlights.

(Please excuse the out of focus pictures - the wife won't let me take the good camera into the barn so all I had was my phone)


I started with a section of 1/2 inch PVC, 45 degree 3/4 to 1/2 inch reducers, 1/2 inch PVC caps, 470 ohm 1/2 watt resistors, the LEDs, and some 18 gauge wire.

I drilled 2 small holes in the PVC cap & fed the leads through so that the LED was inside the cap with the leads sticking out. I then hot glued the LED in place.

I then soldered a 470 ohm resistor to the longer lead (anode, positive) of the LED. I plan to run these from a common 12 volt power supply, so I'm not using a battery box. You could use 4 AA or D cell batteries if you replace the resistor with a 120 ohm resistor, or a 9 volt battery with a 270 ohm resistor. NOTE: I used a 470 ohm resistor because I plan to power these with 12 volts, and with the specs of this particular LED it turns out that's the value I need. If you're going to use different voltages or different LEDs, you'll need to calculate the resistance for your particular setup. You can find a great LED calculator here.

Then I soldered a red wire to the resistor, and a black wire to the other lead of the LED (cathode, negative.) I insulated the bare leads with heat shrink tubing, but electrical tape would work as well. Just make sure the bare leads don't touch each other.

I then fed the wires through the 45 degree fitting and nested the pipe cap into the big end of the 45.

Next, I cut a piece of the PVC pipe about 8 inches long, but made the cut at a shallow angle so the end would have a point. I then drilled a hole a couple of inches from the straight end of the pipe, and fed the wires through the straight end and out the hole. After that it was just a matter of pressing the pipe into the fitting.

There you have it. A quick shot of black paint & you have small, nondescript, bright spotlights perfect for lighting tombstones or props. Just stick em in the ground and go.

Oh, and did I mention they're bright?

Here's one of them illuminating the gardening tools (the scariest things in my barn) from about 6 feet away.

There ya have it, hope ya like it.

Saturday, August 1, 2009