Half a croissant, on a plate, with a sign in front of it saying '50c'
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Replace "light" with "sausages" and this may work...

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post-it explosive

for 007 movies only...
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James Bond in enemy territory...he spots huge container having inflammable material...takes out a post-it pad out of his pocket...writes '2:00' on it using an ordinary pencil...and sticks the post-it on the container...the moment he sticks it..the time starts ticking...the hand written time of '2:00' starts ticking down..and we see handwritten '1:59', 1:58'...etc as time changes...

then for some reason he feels even a minute is not needed for his escape...so takes an eraser from his pocket...rubs off the time..writes again as '0:20'...so again time starts ticking from this...and when time reaches '0:00'...it creates a hole on the container and creates a small spark which engulfs the whole place...kaboooommm...

he he...always imagined to see something like this in bond movies after seeing all those gadgets which impresses us

ravi kris334, Aug 23 2011

(?) LCD writing tablet http://www.brooksto...=L2_Kitchen|L1_Home
But smaller. Allows for the sticky note to be "refreshed" with a new number during countdown. [DIYMatt, Aug 23 2011]

[link]






       OK, because this is a visual joke only, and not a technical invention, he'd also have to draw a bundle of dynamite sticks, or similar, on the post-it.
pertinax, Aug 23 2011
  

       Just after 0:00, the hand-written timer is replaced by a cartoon explosion and the word BOOM!   

       Actually, this doesn't have to be just a joke. What we're talking about is either one of two things:   

       A) a timed-release corrosive agent with volatile properties, contained in a thin strip with adhesive backing, or   

       B) a paper-thin thermite grenade, again with adhesive backing.   

       Either could incorporate an LCD timer display (with 'handwriting' font, to satisfy the gag). The halfbake here is in how to make it thin enough to carry around a 'pad' of them.
Alterother, Aug 23 2011
  

       Pretty sure you could get the thermite, detanator and clock thin enough. It wouldn't quite be paper thin, but definitely no more than a milimeter, and flexible. I'd say the halfbake is trusting handwriting recognition that far.
MechE, Aug 23 2011
  

       It would be activated by the sharp, sustained pressure of the pencil. Actually writing the number is just for cinematic purposes.
Alterother, Aug 23 2011
  

       The writing pad could be electronic, like an e-paper refrigerator board (these exist) and a small circuit could be programmed to recognize handwritten numbers, then display a countdown based on those numbers. The whole thing could be adhesive backed thermite or maybe just a thin sheet of plastic explosive with a detonator. Expensive and slightly thicker than paper, but probably doable.
DIYMatt, Aug 23 2011
  

       // huge container having inflammable material ... it creates a hole on the container and creates a small spark which engulfs the whole place... //   

       This detail of the scenario is why I suggested thermite, especially because it is already available in paper-thin- strip form; conventional explosives are the obvious choice, though.
Alterother, Aug 23 2011
  

       // definitely no more than a milimeter, //   

       Ever the optimist ...   

       // probably doable //   

       You reckon ? We don't.   

       Even in a millimetre-thick sheet, the explosive will have to sacrifice brisance for mechanical properties; there will need to be substantial proportions of binders and other compounds which will reduce the NEQ.   

       Laminar explosives have some interesting properties, but producing their major effect at right angles to the plane would require them to be initiated simultaneously at many points around the perimeter. Given propagation delays, that means that the corners have to fire first, then the centres of the sides. It's like the implosion "squeeze" in a fission weapon, only without lensing.   

       That means that multiple electrically-linked and sequenced initiators need to be distributed right round the edge of the sheet, with no mechanical protection from friction or impact. Lead Azide is acceptably insensetive for a primary, but even so, leaving little particles of it to flap in the breeze like that, unprotected from heat, friction, static or impact, is not a good idea, particularly when it's attached to a sheet of high explosive.   

       Not merely halfbaked, totally impossible.
8th of 7, Aug 23 2011
  

       Even thermite or corrosives?
Alterother, Aug 23 2011
  

       [8th] You'll notice I referenced thermite, not explosive. That is effective in a "burn through" format rather than a sequenced explosion. Admittedly, it would probably only work on a thin walled tank, but it could work.
MechE, Aug 23 2011
  

       Especially if placed on top of the tank, where it wouldn't run. On the side, it would probably just leave a long scorch mark.
Alterother, Aug 23 2011
  

       // it could work //   

       ... on an empty aluminium beercan.   

       Thermite is either a powder or a dense solid. To make it conformable, you'd need to combine it with a plastic matrix, reducing the payload and changing the stoichiometry; because of the large surface area, at least 50% of the heat energy would be immediately lost to the atmosphere on the outboard side. And you still need a high-yield thermal initiator which is sufficiently compact and insensetive.   

       Thermite devices tend to have form factors that minimise the volume to surface area ratio; cones, cylinders, ovoids, frusta.
8th of 7, Aug 23 2011
  

       My knowledge* of thermite is strictly practical: how to make it, how to use it, and how to misuse it.   

       *by this I mean 'what I learned while working for the railroad', so 'knowledge' may not be the most appropriate term.
Alterother, Aug 23 2011
  

       Since you are apparently still not dead, you have clearly grasped the most salient facts about handling thermite.
8th of 7, Aug 23 2011
  

       I have. I've even manufactured my own, and for legitimate uses, at that. That I have yet to severely incinerate myself is a testimony of the skill of the trackside chemist from whom I learned.
Alterother, Aug 24 2011
  

       Or, and this is far more likely in your case, pure dumb luck...   

       "Build a man a fire, and he'll be warm for a day; but set a man on fire, and he'll be warm for the rest of his life."
8th of 7, Aug 24 2011
  

       Ah, that legendary Borg diplomacy!
pertinax, Aug 24 2011
  

       //... on an empty aluminium beercan. //   

       That's still working. And if the plot requires that the Bond Villian keeps his highly volatile experimental chemical in an empty beer can, then so be it.   

       (Pretty sure you could do a little better than that with the proper shape, choice of binders, and possibly an ultrathin mylar front side. Sure it would burn out quickly, but for a fraction of a second it would direct more heat to the rear)
MechE, Aug 24 2011
  

       I was toying with a related idea: A post-it soaked in Nitrogen Triiodide with excess Ammonia- becoming unstable when it finally dries. When someone tries to remove the post-it, it changes into a cloud of yellow confetti.
Ling, Aug 24 2011
  

       When the timer reaches "0:00", the text gets replaced with "BOOM!"
metaforth, Aug 26 2011
  

       //       Just after 0:00, the hand-written timer is replaced by a cartoon explosion and the word BOOM!    //   

       --[The Alterother], Aug 23 2011
Alterother, Aug 26 2011
  

       //then for some reason he feels even a minute is not needed for his escape...so takes an eraser from his pocket...rubs off the time..writes again as '0:20'//   

       He'd have to be careful when editing the time so as never to leave it blank or zero; perhaps changing "1:00" to "1:20" and then changing the minutes digit from "1" to "0".
phundug, Aug 29 2011
  

       [+] scripting options would include drawing 'start' 'stop' and 'password' buttons.
FlyingToaster, Aug 29 2011
  

       Reality check:   

       A typical post-it note is about 60mm x 60mm; that's .0036 of a square metre. At (generously) 120gsm weight, each sheet weighs about 0.4 of a gram.   

       Even with a primary explosive (which is not the best thing to be carrying loose in a trouser pocket), that .4g is going to make a loud noise, but not much else. And applying pressure to a 1.1A compound with a ballpoint pen is an excellent recipe for "Goodbye, Fingertips !"   

       Given the physical, chemical and mechanical constraints of conventional explosives, it's a non-starter. Even some of the newer and more exotic ones don't begin to come close.
8th of 7, Aug 29 2011
  

       Maybe he doesn't use a single sheet at a time. Take the 1mm thickness I mentioned above. That is 3.6cm^3. Assume .6 cm^3 is detonator, timer, OLED screen, whatever.   

       Assuming HMX explosive, it is equivalent to more than 10 grams of black powder or 5.8 grams TNT. While still not super impressive, it's approximately the force of two 12 gauge shotgun loads, which will punch a hole through most sheet metals at point blank range (even without a slug). Admittedly, this may be slightly less directed, but I still think it's possible.
MechE, Aug 29 2011
  

       But the shotgun loads are contained within the barrel. Without a tamper, most of the energy is wasted; and you're basing your calculations on pure HMX which is a brittle, crystalline solid, not a flexible laminar structure.   

       Let us once again draw your attention to the isue of simultaneous peripheral initiation… if the detonation propagates from a single point, then the pressure wave will be at its peak in the axis of propagation, not normal to it as this idea requires for effect.   

       A device to fulfill the specification would need to look like a yo- yo, or half a ping-pong ball. Post-its don't tend to lie perfectly flat, either, and any air-gap or curvature would significantly compromise performance.
8th of 7, Aug 29 2011
  

       Multiple layers. Ignite the outermost layer first, it provides a back stop for the detonation of the remaining layers. If the detonator for this layer is in the center, it triggers the inner layers when it reaches the edge.   

       Deliberately shape the material to form a concave on the underside for a minimal shaped charge effect.   

       As far as binder, C4 is 94% RDX, I don't know what is possible with HMX, but I assume something similar, I figured that as part of the .6cm^3.   

       I'm not saying this is going to produce a massive explosion, but enough to punch through a propane tank, or knock the valve off a compressed gas cylinder? I think it's possible.
MechE, Aug 29 2011
  
      
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