I'm still alive...

...really. Sorry for the absentee-ness. Life has a way of changing your plans every now and then. I'll be back soon... J

Vending machine motor. Quite possibly a haunters new best friend.

New toy

I've never used anything but a PC to control my displays in the past, so I thought I'd play around with a stand alone controller or two this year. The Nerve Center from Monster Guts showed up on my doorstep today - can't wait to try it out!

The Waxybottom expedition

In 1918 a British expedition led by the intrepid Nigel Q. Waxybottom set out for a small island east of Bimini in search of the tomb of the tyrannical King Whatalottahooie. They were never heard from again. Some say they were lost to the sea, while others claim they fell prey to the curse of the candy king...






This was how I greeted my TOT's...

(sorry about the dark vid - more on that below)





All in all things went well this year, in spite of the few hiccups I had. The kids really loved it.

Lessons learned:

When you find something you want to use in your haunt, buy it then.

I found some really awesome green nylon camo netting at a local surplus store that I'd planned to use as a backdrop for the entire display, but didn't buy it when I first saw it. Then when I went back for it last weekend, they were sold out. D'oh!

When you build custom parts or effects, don't use oddball parts you can't easily replace.

I built some LED flood lights using some really high power LED's. I didn't have a 12V power supply with enough current capacity to power them (wanted something more weather tight than a PC power supply) so I used a 19V supply from an old printer I had laying around. The power supply died & I didn't have another one to replace it, nor did I have time to change out the resistors in the lights so I could use a different voltage. Wasn't a huge deal, but the yard was quite a bit darker than I wanted.


On another note, I've come to the conclusion that the skull I used for the idol is cursed itself & I shouldn't use it again. I've repurposed it for different props 4 times now, & every time it's broken on Halloween night. I think from now on it will be a static prop...

Happy Halloween all!

A little last minute testing

Sorry for the shaky video.

This years lineup

And so it begins

Calculator software

I've done a bit of (very simple) computer programming in the past - mostly scripts to automate some server actions & reports - but never anything with a GUI. Recently, however, a change in some procedures at work has prompted the need for some custom software to bridge sales tracking and cash handling (yawn...). So what the heck does that have to do with Halloween?!? Not much, really, except that in the process of wrapping my head around Tkinter I've managed to write a little utility that encompasses most of the calculations I've written about in the past.

(I know - most of these calculators are available online already - it's really more of an exercise for me. Somebody may find it useful, though.)

There are both Windows and OSX (Intel only) versions. Feel free to download and/or redistribute all you like. All I ask is if you do redistribute it, please link back to this blog. I'd also appreciate any feedback you might have.

Enjoy!

More on powering LEDs

I've had several questions lately about powering LED spotlights, so I thought I'd see if I can't break it down a little better.

First off, there are 2 ways wire a group of LEDs - series and parallel.

Series: (or what you don't want to do)



In a series circuit, the negative lead of the first LED is connected to the positive lead of the next LED. and so on down the line. In this configuration only 1 resistor is used for the entire circuit. In a series configuration, the number of LEDs you can use is limited by the voltage of your power source. If you have 3 LEDs with 3.6 volt forward voltage wired in series, you couldn't use a 9 volt battery to run them because the total forward voltage is greater than the supply voltage (3.6 + 3.6 + 3.6 = 10.8 volts). I don't recommend this configuration for a few reasons, but mainly because if one point in the circuit fails you'd lose all your lights.


Parallel: (the easy way)



In a parallel circuit each LED has it's own resistor, and the positive leads of all the LEDs + resistors are tied together, and the negative leads are all tied together. When your LEDs are wired this way, the factor that limits the number of LEDs you can use is current (amps).

When you calculate the value for the resistor you need for your LED, one of the values you need for the calculation is the current rating of the LED. If we assume that the calculations are correct, then that current rating is the maximum current that will be flowing through the light. So all we need to do is make sure the total current of all your lights isn't more than your power supply is capable of providing.

So for example, lets say your LED has a current draw of 20 mA. 20 mA (mlliamp) is 20/1000th of an amp, so if you had a 1 watt wall wart, you could run 50 LEDs. I don't recommend loading a power supply to it's full capacity, so I wouldn't run more than about 40 LEDs (80% capacity).

It is possible to wire LEDs in a combination of series and parallel, but I'll go into that another time.

Method of switching audio between multiple speakers. Also switches spotlight on prop that's "talking".

reversing polarity

(Just needing a place to put an image...)

Just a quickie

Threw together a couple of lanterns for my yard today.


Pretty simple, really. Just a couple of old jars I dug out of my neighbors garage (with her permission, of course.) I left the inside as dirty as I found them, but wiped the outside so I could dust them with pumpkin orange paint. I wrapped some fine steel wire around the top & twisted it so I could loop handles made from a wire clothes hangers through. I extended the hanger wire over the top & fastened one of the little clip on LED lights from Jacks tool shed. I didn't use the clip - I just taped the light to the wire.

Not sure yet how I'll display them. Thinking about a couple of pumpkin sentinels. Not much time to play...

Sounds like...

I was looking around for a .mp3 player solution for a prop I had an idea for (more on that later), and came across a couple of boards at MDFly.com.




The SD/Thumb drive board behaves just like a regular .mp3 player, but has the advantage of having the controls readily available so you don't have to tear one apart & hack the controls to use it. MP3 files can be stored on either a SD card or a USB thumb drive.



The board that really piqued my interest, however, was the serial TTL interface SD board (sold out as of this writing - sorry). This board is controlled by TTL level serial commands, making it a prime candidate for control by an EFX-Tek controller or a pic or Picaxe microcontroller. The board supports direct play of up to 199 .mp3 files, as well as random playback of a single track.

I have both these boards and can verify that they do work as advertised. Now to use them in a prop... :)

One of those "why didn't I think of that" moments

Just ran across this really cool reststor value card over at Instructables. One of those cool little things that can make life easier. I keep a resistor color chart pinned to the back of my bench, but this would be much quicker and easier to use.

Capacity for capacitance

And then there's the capacitor. Simply put, a capacitor stores electricity. When a charge is applied to the capacitor, it is stored until a path is available for the current to flow. You might think "Oh, so it's like a battery." (C'mon, admit it. You might think that...) Well, it is and it isn't. Aside from the technical differences in how they're made, (a capacitor is a series of plates separated by an insulator, a battery consists of plates made of dissimilar metals suspended in an electrolyte) the capacitor charges and discharges very quickly, while the battery takes it's own sweet time.

The ability to charge and discharge quickly makes them handy in a couple of ways. Using a capacitor in parallel with a heavy reactive load like a motor or power amplifier can provide an extra "shot" of power when a load is suddenly applied. That's handy if you want to put big subwoofers in your car, but isn't used too often in a yard haunt.

What does come in handy is the capacitor's ability to filter out spikes in voltage. Halloween props very often involve the use of devices like pneumatic solenoids, relays, and motors that present a highly reactive load to a power supply. It's also very common for those props to be triggered or controlled by sensitive controllers. Putting capacitors in parallel with the power leads of the controller smooths out any voltage spikes the props might create. The charging and discharging of the capacitor smooths out the peaks and dips in voltage.

Think of it this way. Lets say your highly successful haunt has a straight queue line. As people come up in groups of 2 or 3 (or 10) the pressure on the line (voltage) rises and falls.



Now if you take a chapter from Disney's attraction design and add a "stretching room" like the Haunted Mansion, the flow of people is smoothed out.



Capacitance is measured in farads, and capacitors have a maximum voltage rating. For filtering purposes the smaller the farad rating, the faster it charges and discharges. That means that smaller capacitors filter higher frequency spikes, while the larger ones handle lower frequencies.

Playin' around with VSA

OK, so in the past I've used I.R. sensors & pressure mats to trigger props. It's always worked OK, but there have been times when the triggers failed, or the timing was off, or (worst of all) the props have been too frightening for the young TOT's & I've wished they didn't fire. I like the of manually triggering the props, but don't want to be tied to a wired control panel. I could use a simple wireless remote, but why do that when I can do it a much geekier way?



The routines in the video are just audio only examples, but they are .vsa files. I'm using Monkey Basic's awesome Helmsman to pre-load the VSA files, and a free program called EventGhost to trigger them. EventGhost has a web server plug-in that lets you create web pages with buttons on them that can trigger events on the computer. (EventGhost can do lots of other things, too. The learning curve is a little steep, but once you're past it you can do some really cool stuff.)

The video's just a proof of concept & I still have a few bugs to work out, but it works!
Once I get the kinks worked out I'll write up a how - to.

enter the drago - er, ah, diode?

This is an easy one - Put simply, a diode lets current flow in one direction, but not the other. Kinda like a check valve.



A couple of things to remember about diodes - a diode will cause a bit of voltage loss in a circuit. This is referred to as forward voltage drop, and is usually around .5 - .7 volts. Diodes also have a maximum reverse voltage. If this is exceeded, the diode will break down and allow the current to flow in the wrong direction (that'd be bad, mkay?)

The polarity of a diode is denoted by a stripe on one end of the diode. Current flows into the end furthest from the stripe and passes out the other, but not the other way 'round.

Transistorized...

Aah, the transistor. Where would we be without it? For starters, I wouldn't be sitting on the couch writing this post. The computer would be a bit too big and expensive for that, what with all the vacuum tubes it would take to make it work. As it is there's far more processing power in my laptop than there was on the Apollo space capsule that put men on the moon, thanks to the transistor.

But what is a transistor, exactly? A transistor is a semiconductor that allows a low current to control a much higher current. (I'm not going to go into what exactly a transistor is, 'cause it's boring.)

I'm going to limit this post to basic bi-polar junction transistors, although the basics apply across many other types of transistors as well. Transistors can be used to amplify current, or be used as a switch. For the circuits I'll be building for my haunt the transistors will be primarily used as switches, so that's what I'll focus on here.

There are two types of bpj transistors - PNP & NPN. This refers to the polarity of the junctions in the transistors, and determines how they are connected and used.



Transistors have three connections - the base, emitter, and collector. In a NPN transistor, a small amount of current applied to the base allows a larger current to flow from the collector to the emitter and on to ground.



Power is connected to the load, and the negative connection of the load connects to the collector of the transistor. A small current applied to the base allows the current to flow from the collector through the emitter and on to ground, completing the circuit.

In the above diagram you'll notice a couple of resistors. The resistor between the base and the trigger source is vital to the longevity of the transistor. The connection between the base and the emitter has very low resistance, and when power is applied to the base the connection is close to a short circuit. This would cause what's called "thermal overrun" (a fancy way of saying the transistor would get really hot).

OK, great. So we need a resistor, but how do we know what resistor to use? Too much resistance and the transistor won't reach saturation and pass the full amount of current needed, too little resistance and too much current passes through the transistor and it burns up. Never fear, there's a way to figure it out, & all it takes is a little math (you know, the stuff we learned in school that we never thought we'd need to know...)

When you look at the specifications of a transistor, you'll see DC collector current and hFE. The DC collector current is the highest sustained current that the transistor can handle, and the hFE is the forward current gain (not sure why they call it hFE, but if they called it fcg we haunters might confuse it with a flying crank ghost.) To figure out what value resistor we need, we have to figure out how much current the base requires for the transistor to reach saturation. This is simply the DC collector current divided by the hFE. So for example, if we have a DC collector current of 5 amps and a hFE of 1000, the base current would be .005 amps, or 5 milliamps. To ensure saturation it's a good idea to increase this a bit, so we'll multiply the base current by 1.2 in our final calculation. To find our resistor value we go back to Ohm's law - V/I = R. Assuming we're dealing with a 12 volt circuit, our calculation would be 12/(5 / 1000 * 1.2) = 2000, or 2K ohms.

The other resistor in the circuit isn't critical, but can help if you have erratic switching. In the case of the NPN circuit the resistor is considered a pull-down resistor. It's job is to hold the base low when no trigger voltage is present. The value of this resistor isn't critical, but should be significantly higher than the base resistor. A good rule of thumb is to multiply the base resistor's value by 10 for the pull-down resistor's value.



A PNP transistor is similar to the NPN, but instead of applying current to the base to trigger current flow, you apply ground.



In this case power is applied to the emitter, and when the base is grounded current passes through to the collector and into the load.

The resistor calculations are the same, but in this case the second resistor's job is to hold the base high when the transistor isn't triggered (called a pull-up resistor in this case).

Transistors are very versatile - you'll be hearing about them a lot in the future. Unless of course you get sick of my ramblings and quit reading...

Resistance is futile

OK, so we've covered some of the basic terms we'll run into in simple circuits. So now lets look at some of the components we'll use to actually build them.

Lets start with the lowly resistor. A resistor limits the current flow in a circuit (I know, we've already established that.)



More specifically, a resistor is a device that is added to a circuit to control and limit the flow of current. The resistance of a resistor is fixed and not affected by the flow of current or changes in voltage. (There are variable resistors, but they don't count.) (OK, they kinda count, but we're just talking about plain old resistors right now.)

For some strange reason, resistors aren't marked labeled with plain markings. That would be too easy. Instead, they're marked with a series of colored stripes. The colors denote the value and tolerance of the resistor.



Resistors also have a wattage rating that denotes the overall safe power rating of the resistor.

There are some really good resistor color code calculators online.

Watts the deal?

In my last post I tried to explain voltage, current, and resistance. Not too sure how well I succeeded, but no matter. Ever forward, right?

There's one more term that we'll see frequently - watts. Watts (W) are a measure of power, and are calculated by multiplying current by voltage. So if you have a 100 watt light bulb that runs off 120 volts, that bulb would draw .84 amps (100 watts divided by 120 volts). Pretty simple, huh?

So, what's the benefit of knowing all this, you may ask. Well, for starters you can figure out if you have enough power to run your haunt before you overload your power supply and burn your yard up (that would be bad). Just add up the total amperage draw for each circuit & make sure your power supply has a high enough amperage rating to exceed the total load.