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Sensitive Tilt Trigger

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Picture of Sensitive Tilt Trigger
Mk2TiltSwitch.jpg
Designed for any purpose that might need a very sensitive, any-direction, do-not-tilt switch. This instruction describes construction of: 1) My initial, hand-built prototype, thrown together in a single afternoon out of spare parts merely as proof of concept; 2) The follow-on, 2nd generation prototype; and 3) circuit board layout for a final design not yet etched and built. For reference I will call them the Mk1, Mk2 and Mk3 tilt trigger mechanisms. During that first hasty effort on the Mk1 I learned a few object lessons. I labored to circumvent these in the Mk2. Ditto from the Mk2 to my as yet unbuilt Mk3 design. I'll describe the lessons learrned so that you may not repeat my own mistakes. First photo shows you the rough-finished Mk1 prototype which I built almost entirely of parts from Radio Shack. Second photo is of the Mk2 which inc ludes some parts from a national chain hobby store.

Parts List for Mk1 sensor:

Two Circuit boards, Radio Shack 276-148
One CMOS 4011 quad NAND gate
Two resistors, 10M
2 sq in of metal duct tape
Some 30 guage wire wrap wire

Additionally the Mk2 requires:

Thin copper foil.
Thin brass wire (stiffer than resistor leads).
Epoxy  cement

Also shown in both photos is some ancillary circuitry tossed into the project just to make demonstration easy.  The add on circuit is nothing but a 555 timer in monostable mode with a red LED for visual output to show when the sensor trips. As this timer circuit is can be had from Google (and found in data books going back to since I was in high school) I won't detail that part here. But for reference, these are the parts I used to built that circuit too.

One LM555 timer
One resistor, 18M
One resistor, 560R
One capacitor, 1uF
One capacitor, 10nF
One LED, red

The 1st picture shows the Mk1 sensor and ancillary timer, all in one (crudely built) package. The 2nd photo shows the Mk2 slightly less crudely constructed.

 
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Those little round Honeywell furnace thermostats have a little mercury filled tube inside them that can be salvaged for use as tilt OR position switches (limit).
They have contacts on either end inside the tube and some short lengths of wire on them if clipped out of the thermostat body very carefully.
To get the tube off of the bimetallic coiled sensor spring , just bend the metal back and forth near the tube to just break it off.
They are sealed and safe to use as long as you don't break them open .
They can be mounted to other things using 100% silicone adhesive or caulk.
For safety , I suppose that the mercury filled glass tube could be encapsulated inside of a small metal tube .
Captain Napalm (author)  Mechanic20112 years ago
The idea for mine was that it should sense change of tilt from any angle. To use Hg I'd inject a small blob into a ping pong ball which had tacks driven for the contacts. But Hg is toxic, as I am sure you must know.

I seem to be having issues with the feedback feature. I tried to post this reply once but it seems not to have taken. Hope this one isn't double.
That's why I stated to encapsulate the mercury switch glass tube inside of a small metal tube with silicone sealer.
It will contain it just in case.
The metal tube can also be used for mounting the whole thing rigidly so it isn't loose.

Captain Napalm (author)  Mechanic20112 years ago
So you said, but the purpose built tilt tubes from thermostats are designed for only a single orientation. It has to sit a certain way and only trips when tilted in a single direction. The ball-in-a-cage works for most any orientation, better for some than others, though.

Hg inside a tack-pierced, spherical ping pong ball would work for every possible orientation. But the circuit would need be more complex. I am pondering that option now.
Yes , I thought about that .
A person would need several of them mounted in whatever orientation that you needed.

What about some of those plastic Easter eggs sold in stores around Easter time that can be filled with sweets for the kids?
They split in half to get the contents either into them or out.
Now put foil contacts INSIDE the egg halves with the wires going through the wall to the outside of it.
You could also use small pieces of copper flashing material which would make it easier to solder the wires to the contact patches or narrow strips .
I see that stuff once in a while at the metal recycling yards.
When you are ready just insert the steel ball bearing and glue it together.
The egg could be mounted in any position you wanted it to be in.

Its along the same idea as your ping pong ball idea only safer.

This is still a good instructable though !!
Good job.
I like the open frame idea of it.
Captain Napalm (author)  Mechanic20112 years ago
Keeping with the idea of ping pong balls for their spherical (versus egg) shape, Testing ping pong balls on different solvents I find that they can be dissolved in acetone. In this way we can make a sealant/glue for a stage I'll describe shortly.

Using a Dremel tool we drill tiny holes spaced in a geodesic pattern all over the outside of a fresh ping pong ball. Those holes we make to be 0.016 inches diameter which is the same size of brass rod available at hobby stores (the kind that sell kits for RC planes & cars). Brass solders easily and is also plenty stiff. So tiny brass rod is what we'd use for our contacts. For each hole we'd cut a short length of brass rod after first soldering on a fair length of copper 30 AWG lead wire. Once cut free, we'd push the tiny brass rod into a hole in the ping pong. Once situated we'd fix it in place with our home brew sealant. We do that all over the ball. So now it is like an inside-out sea urchin for having brass pins on the inside. It is also kind of hairy for having many lengths of 30 AWG wire draping from the outside.

Now we drill another hole into the ball, this one somewhat larger. Into this we can pour either: A) a dollop of mercury [salvaged from a Honeywell thermostat] or B) some tiny metallic craft beads [like was done in another instructable recently posted]. Then we seal up that final hole.

Now the whole assembly would be kind of fragile. So to secure it for rough use we paint it over with either: A) polyurethane; or B) epoxy.

For wiring we could short every 2nd pin in the geodesic pattern to high. The remaining pins could then be either wired all together for a simple do-not-tilt sensor.

Or, if we wanted to measure the tilt instead of just sense it, we could employ an Arduino. For that we'd need some kind of polling algorithm. I could puzzle one out if I chose. But if going to all the trouble to use an actual Arduino, then we may as well have just used an I2C 3-axis accelerometer in the first place. And there are already sketches a plenty for that.
rhoaste2 years ago
I'm trying to think of a good use for this other than a trigger for a bomb.
motorcycle anti-theft trigger for sms and/or "screamer"
rhoaste rhoaste2 years ago
...That said, It might be useful as a switch for orientation if multiple pins were used.
Electorials2 years ago
it's a nice idea but does it work fine too?
does it happen that the ball doesn't make good contact sometimes?

Nice instructable :)
Captain Napalm (author)  Electorials2 years ago
The prototype thrown together in an afternoon using an octagon instead of a circle? Using slightly corroded, 10 year old, 3rd hand resistor leads instead of new? Using an out-of-round slingshot ball instead of perfect sphere bearing? No, this first effort has a few issues, as I explained.

I have another in the works, a PCB designed in KiCad, which will address those issues. For this I did some math on the geometry instead of rooting around in drawers for what I could find. It'll work better.
Ok :)
You used quite large resistors...
Captain Napalm (author)  blinkyblinky2 years ago
Instead of physical size, did you mean value? I often choose 560 Ohms for an LED when I want it to light tolerably well on four AA batteries and not be damaged long term if plugged into a car's cigarette outlet. And 10M is fine for pulling CMOS to ground in this instance. If it's to run on batteries, I try to avoid wasting current as much as I can.

And if you did mean actual size, I've got hundreds of those from hand-me-down but very few SMDs to spare on a quick knock off.
Yes, I meant value.
fjordcarver2 years ago
You can just tape the wire to the tape with a small square. I used this technique for a much simpler project. http://www.instructables.com/id/Business-Card-Inputs-and-Outputs/
Awesome job by the way!
Captain Napalm (author)  fjordcarver2 years ago
That's a good idea. I edited the instruction to include that option.
florinc2 years ago

Designed for any purpose that might need a very sensitive, any-direction, do-not-tilt switch.


What application did you have in mind, if you don't mind?
Captain Napalm (author)  florinc2 years ago
A burglar alarm you could just throw into the saddle bag of your parked Harley outside the motel at Sturgis? A toy landmine for LARP enthusiasts reenacting WW2? A someone-is-on-my-porch sensor that won't trip on flyby bats like a PIR?
hopsman2 years ago
I think that the author's nickname and the tool itself paint a scary picture. This might belong in the Anarchist's Cookbook.
Captain Napalm (author)  hopsman2 years ago
FYI: Here I am channeling Calvin from Calvin and Hobbes. Maybe that's almost as scary all by itself?
H202 years ago
So it's pretty much an accelerometer?
Captain Napalm (author)  H202 years ago
No, accelerometers are ratiometric. This is a simple switch with digital pulse output.
REA H202 years ago
No, an accelerometer measures positive and negative acceleration. This device just senses orientation based on gravity.
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