Friday, 15 March 2013

Zippo Burglar Alarm

This is another old project that I originally posted over at Instructables. If you want to have a go at making one, check out the original posts.

... And this piece represents society's self destructive nature

This idea began with my obsession with Zippo lighters, and I suppose that all started with a childish fascination with fire (I still list burning things as one of my hobbies). 
But now it's more than that, I love the Zippo design because of it's simplicity, a wick petrol burner, the satisfying click of the cam hinge, the easily replaceable parts, rugged metal construction, all come together in a neat pocketable enclosure.
It's got ties with the army, it's a hollywood icon, not mention that they're just plain cool.

I used to carry a zippo all the time, but now it lives in my toolbox. These days my love of Zippos manifests itself as seeing what gadgets I can cram into them, and occasionally setting my trousers on fire.
Which brings us back to the Zippo burglar alarm.

A quick bit of googling set me up with the simple electronics knowledge I'd need to make an infra red proximity sensor, I mocked one up using a PicAxe chip to do the heavy lifting.

 | Warning! Poorly Explained Tech Stuff | 

A basic IR proximity sensor works by shining an IR LED at a receiver whose resistance will change depending on how much IR light is hitting it.
You can place the emitter and receiver on opposite sides of what you are trying to detect, but it is easier and more compact to use reflected light. I.E the led (clear part at top of image) sends out it's beam , if an object is with 20cm the light will reflect off of this object back to the sensor (black bit just to right of led) and trigger it.

For my project I'm actually using a digital sensor. The difference being that it will only trigger when it receives a very specific coded signal from the the LED.
This is much more secure and isn't subject to ambient light or other interference.
Generating the specific code is done by my chip. Then, when the sensor is set off, my chip will trigger the red LED and the piezo transducer. These gold discs are nice simple ways of making annoying noises (think pre-polyphonic ringtones).

The push button is just there to select the various different program modes I put on the chip.

 | Warning! Poorly Explained Tech Stuff | 

So now that my circuit was working on that breadboard the task would be squeezing it into such a small space.

First job was to plan out my circuit in extravagant, illustrated fashion.

Mock up of the main board

This battery board, occupies the Zippo lid.

Constructing the actual boards took an incredibly long time. One of the main problems being trying to insulate everything. Zippo cases are made of brass so I was afraid of shorts. I was insulating everything as I went along with clear epoxy, which was fine until I tested the circuit and it didn't work.

After a few hours with a multi-meter I found a short buried under a mass of epoxy where I had glued two boards together. After deciding that chipping away the epoxy would just cause more damage I decided to sever the connection and re-route it with some wire.

The battery board was mainly a pain just trying to fit 3 button cells under it and cram it into the lid.

I wanted to retain the classic snap action of the Zippo hinge and remaking it seemed tricky, so I opted to just hack up the insert.

Less one chimney.

Shorten significantly and relocate the spring.

I had all the pieces, now I just had to smoosh them together.

Piezos normally have special enclosures to increase volume. That would have taken too much space so I just expoxied it to the side of the case, which improved the output significantly.

I insert the main board, so that the LED pokes through this convenient hole.

Side note, those markings on the base of the Zippo indicate the year it was made. Turns out this one (£5 off eBay) was from 1984. If I'd known that I wouldn't have defaced it. 

The smaller board screws into the lid (securing the batteries) and what's left of the Zippo insert push fits to keep the rest of the guts in place.
I did make a little sleeve for the IR LED but it has a 30ยบ beam angle so only reflected light will set off the sensor.   

You can see it working in this old video*

I made this as part of the gift exchange, so I no longer have the original. But now that I've got my CNC mill and can make nice neat circuit boards, I've added remaking this to my to do list, along with a million other 'zippo gadgets' .

R/C Zippo

Camera Zippo
Torch Zippo - Actually working on this.
MP3 Zippo
Infinity Mirror Zippo
Hermit Crab Zippo
Laser Pattern Zippo
USB Card Reader Zippo

Maybe someday I'll get around to building some of them.

* Please forgive the quality, I still haven't gotten the hang of making good videos but this one still makes me cringe watching.


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