EEVblog #191 - Mouse Trap Triggering

What's the easiest way to electronically trigger a mouse trap? Dave has an idea...
Just don't ask why, OK, Dave doesn't know either...
Also a tutorial on resistor power dissipation.

[garychap]

Nichrome wire would be more efficient and much faster I think.

A more challenging problem is how to train a rat to turn on the bench supply : )

[douglas]

What I like about this video, is that is shows a simple, cheap way to trigger a spring or cut a holding string. Sure, there are solenoid units that will do the job, but they weigh more, cost more, and have moving parts and there are more things that can go wrong. This method is cheap, simple, low cost, low weight and reliable if the resistor is only used once. Great video and genius idea.

[sciguy]

Also, (and this is super nitpicky), Kelvin is not a degrees measurement. It's just 80 Kelvin - not 80 degrees Kelvin, for example. My Chemistry teacher used to yell at us when we said "degrees Kelvin"...

[wayneherby]

That's not a mouse trap, now THAT's a mouse trap :P

[KozmykJ]

Pull the pin with a bi-metal strip. and you've got a resettable current/heat triggered trap.

[jhoward]

A very creative and simple idea to get the brain juices flowing! I actually liked your creativity. I was expecting you to do something that would require more, but was happy to see how simple you made it.

[AntiProtonBoy]

Regarding the thermal dissipation via the resistor leads, I think it would have been worthwhile to mention that hot resistor leads can stress solder joints, and cause premature failure in some cases.

[sciguy]

Brilliant idea - never would have thought of something some simple. The obvious disadvantage is that it's a one-time-use scenario. But I suppose that even with a solenoid you'd still need to reset the device...

[EEVblog]

@axel1973w You missed the point entirely. It's got nothing to do with the actual mouse trap, it's just another possible method to one-off trigger whatever widget that it might be suitable for.
The resistor doesn't need power either until triggered.
I've actually seen it used in two different scenarios, both military.

[RNdin]

I've heard of this kind of system being used to cut the reefing bands on parachutes. Also to cut loose drouge chutes after they drag the main out of its container.
Reefing bands are basically a line around the shroud lines of a circular parachute that prevent it from opening to its full deployed diameter, which is often done to reduce the g-loading shock that would otherwise occur if it went directly from packed to fully deployed. Reefing bands are also used to control decent rate in order to limit wind-induced drift.

The reason they are found on parachutes so much is because they are easily triggered, absolutely dead simple, and can be made extremely lightweight. Because they are so simple, they are extremely reliable. Not much to go wrong with a resistance based heater, and resistors aren't static sensitive.

Also, resistors and wire are dirt cheap, so they don't cost an arm and a leg, meaning using 2 or more of them for redundancy's sake isn't going to break the bank.

[philbx]

Great to see some fun stuff from you again Dave!
BTW, I seem to remember someone trialling the fishing line approach as a
trigger to early bushfire detection.
A small DC geared motor with 'winch' setup with microswitch would probably
also be the go, although that's a bit OT re. your fine talk on resistors...

[ibrt]

@jnrolf No, Dave was right. 35 Kelvin degrees = 35 Celsius degrees. Remember we are considering temperature differences, not absolute temperature measurements. Degrees in this case means "degrees of difference".

[EEVblog]

@karmicthreat The original proposals did not dictate that an easy reset was required.

[ibrt]

@jnrolf If the thermal resistance is 140 K/W then it is also 140 degC/W. Kelvin degrees and Celsius degrees are the same size (in other words, when converting one to the other the multiplication factor is 1).

[barcelona]

I've heard of a similar method used as an emergency cut down for high altitude balloons (cut through the nylon lines connecting the balloon). I think they might use nichrome wire though.

[iamtheug]

although this clearly worked and is probably the most elegant, for learning's sake, could you modify a fuse to create a break away?

[Shoetiefly]

I often sail solo at night with the boat's tiller held with control lines. If I fell off the boat, the boat would keep going. I have been considering various inexpensive one-off MOB (man overboard) devices to release the tiller if I fell off and a sensor contacted water and triggered the release automatically. I think this resistor burn has potential for this application. A second question for the experts is how to signal the boat while in the water. A small radio ?

[rocketmanprojects]

Thin nichrome or stainless steel wire works well too and it doesn't stink the place up like fried resistor.

[chandin]

I did somehting like that as a kid, though there are times when you need it to be portable and reliable(Operating almost instantaneously everytime). what i did was i got a flash circuit board from a camera and rigged up a cct to trigger it by remote, then i send all the juice in the fat capacitor to a resistor. I used SMD resistors(less than 6ohms). they explode everytime, great for setting off fireworks:)

[jesseespinosa]

I had a similar problem to solve triggering a spring arm at a distance. one 20 guage-ish strand of copper cannot handle much current so I just used the copper as my trigger wire that needed to be cut, 120v dead short across the wire melts the wire for you faster than a 15a breaker can trip. can also be used to light a match at a distance, be carefull though!