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.