Sunday, May 23, 2010

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.

Wednesday, May 12, 2010

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.