Re: Crazy candle project

On 30 Mar 2005 11:40:30 -0800, Andy wrote:

> Hey you guys are awesome. This is for a magic trick as was spotted and
> engineers are responsible for some of the greatest illusions ever
> which is why I came here first. I am sorry about the multiple postings
> (also on sci.electronics.basics) but I saw this group later and
> thought it would be better here. So to clarify the trick , a cup
> (4inches by 4 inches) made of copper is secretly loaded with a candle
> and placed on a table and then revealed a few minutes later.

Expensive cup, but it suggests a possible part of the circuit - a
switch.


|^| ignitor with wires
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| |
---
/ \
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
| |
| |
+--------------+ |
| |
| | | slide copper cup to complete circuit
--- | V
- +-------o o--+
| |
+-----------------------------+
--------------------------------------------
corrugated material to hide wires -- coroplast?

hide battery wherever -- inside candle?

Now you can show an unlit candle without the light setting it off.

> Mike posted a simple solution on the other group :
> "Such complex and potentialy dangerous solutions to a simple problem.
> Take a match and slice into the head with a sharp razor blade. Slip
> a piece of fine wire into the slit and wrap it around the head.
> Solder some larger gauge wires to the fine wires so the joint is
> below the head. Secure the wires to the paper match stick with
> masking tape.
>
> The larger wires won't fuse when you apply a voltage, but the fine
> wire will light the match. Fudge and practice until you can just
> tilt the cup enough to let in light and get the flame near the wick
> - if the whole contraption is inside the cup. You could hide it
> behind the candle. Don't use a flammable cup. Placing the cup on the
> table will extinguish the match, if it's in the cup. If you want
> your audience to see that the cup is empty and there's nothing
> behind the candle, make your own candle around everything - battery,
> sensor, ignitor.
>
> You should be able to set the match off with 1 or 2 batteries - like
> the old 000 steel wool firestarter trick.
> Mike
>
> Followed up by :
> How about use a lunar ignitor for a model rocket motor. It would only
> need about 6V... maybe tie a CDS cell in there for the light sensor.
>
> Ray"
>

I knew them as solar ignitors. If you can get a CdS cell to pass
enough current from a big enough battery ( = fat candle ) to ignite
the thing or the match, that's great. I don't see it happening.

Google on "Fusing Current of Wire in Amperes (approximate)" That
should give you Sphero's table. You'll see that 40 AWG tin wire is
the lowest on the table and even with a CdS cell as low as 400 ohms,
it would take a 112 V source to fuse it.

> I think Mike's idea would work pretty well and not get me killed. I'd
> plan to encase the whole rig inside the wax. I dont know a lot about
> light sensors (except that they exist). Whats a CDS cell that Ray
> mentioned and where online can I buy one. Any better ideas?
>
CdS - Cadmium Sulfide photocell. A light sensitive resistor. Mouser,
Digikey, Radio Sh*t, I guess. You can find circuits for light
triggers via google. Try "electronic rooster". For the hell of it,
let's grab Mouser 338-76c348 with 500k in the dark and 3k - 20k in
the light (that's Zepplin) Iffff... you can get a wire to fuse from
2 1.5V batts like the steel wool trick (test it with just the
battery to make sure it heats and fuses quickly to avoid burning out
your transistor,) great. Otherwise you'd need to use a larger
battery. The safety is kinda overkill as long as you turn the pot
all the way down before adjusting the trigger point, but it'd be
good to have one to safe the thing while it's backstage or whatever.
Adjust it under the same lighting conditions you'll have during the
show.


+------------+--------------+-------------------+
| | | |
| | | |
| | .-. |
| .-. ( X ) Ignitor | safety shunt
| | | '-' |
| CdS | | | |
| '-' +-------------------+
| | |
| 3 V | 100 |
--- | ___ |/
- +----|___|---| 2N3904 or 2N2222
| | |>
| | |
| | |
| .-. |
| 50 K | |<-+ |
| | | | |
| '-' | |
| | | |
| | | |
+------------+---+----------+
created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de

I see one of the chemical solutions is out of the bag. Oh, well. I
guess if some kid wants to pull a prank, there are easier ways. It
*is* the easiest thing. OTOH, you could talk about science and how a
flame will go out without air, blah, blah. Then show them the lit
candle and how fast you can extinguish it with the same cup, proving
the thing *had* to be out while you were talking. Or tell them you
blabbed so much the vibration lit the candle :)
--
Best Regards,
Mike
.

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