Brainstorming for a project has always been difficult for me. Â There’s the saying, “If all you have is a hammer, everything looks like a nail.” I always try and solve a problem with the tools I already have, not wanting to spread out and learn different techniques. Or I’ll get focused on one particular technology I want to learn so I’ll try to use it to solve a problem and miss an obviously and drastically superior solution. I have to think, this project isn’t entirely about me. Obviously, we don’t want to go too far the other direction, but… I think you see my dilemma.
Using the situation discussed in my last post, and discussing more specifically the requirements of the “customer” (Mike), I broke the project down into different parts.
These topics tend to overlap and mix or aren’t needed, depending on the approach we decide to use.
AA or AAA’s
Li-ion / Li-pol
The real question was: Rechargeable versus replaceable. Replaceable would be easiest to design but would require fairly easy access to the batteries, whereas we’re hoping that the great majority of the alarm is hidden inside the boot and inaccessible to potential wrongdoers. Because of this, and that I happened to have a couple on hand, we decided to go with a Li-pol.
Vibration sensor to detect motion.
Accelerometer to detect motion.
Some form of alarm when Mike and the boot get too far apart, not based on vibration.
GPS with a set (or setable) area that will send a notification if that area is left.
Theremin circuit on the handle.
I immediately nixed the GPS idea due to cost, size, accuracy, difficulty of design, and reception indoors. This will be mostly used indoors and if it makes it outdoors, we’ll probably have lost our possibility of recovering the boot. The Theremin circuit was enticing due to its retro electrical style but, depending on the sensitivity, would either make noise when people are just around it or allow people to carry the boot by the soles. Also, with the proximity alarm, I struggled thinking of a way that I could set a distance accurately and not have a false positive. False positives would actually be worse than false negatives, if we tick off the higher-ups. And since accelerometers are more complicated and sometimes more expensive than normal vibration sensors while achieving the same goal, we ended up deciding on the vibration sensor. This may change if the vibration sensor is too sensitive.
GPS/GSM locator to broadcast its location to make it easier to find, in case the boot is successfully stolen.
GPS/WiFi so we wouldn’t have to pay for data packets on the cell
Some form of hot/cold locator.
We decided to not have a locator, mostly for the sake of simplicity.
RFID for Mike Detection, wireless for communication.
Wireless for both, low power for detection, high power for communication.
Car key fob style arm/disarm
Semi-secret switch on the boot to override alert.
Other biometric scanner
Keypad with unique passcode
This was a big issue for me and was difficult for me to decide. After discussion with some of the other junior guys, we decided on the car key fob style arm/disarm. After coming to grips with the limits of passive RFID, I decided that wasn’t the way to go. Then, as a selling point, Brian (a LTjg) explained it somewhat like this, “You can waltz in the room, put the boot on the table, hit the key fob and have the boot make the ‘Buh-bweep!’ sound. That’ll get their attention.” Up until he mentioned that, I was imagining this to be a surreptitious alarm, not to let the people know it was there until the first time it went off. But, he’s got a point. That is pretty stinking cool. As an added bonus, someone mentioned putting LEDs into the bottom two eyelets of the boot and having them flash like a cars headlights. Genius, I say. Pure genius.
Key fob in Mike’s pocket to warn him, either through vibration or an
Have an audible alarm on the boot that goes off when someone steals it.
Have a cell unit that calls his phone to tell him when it’s been stolen.
If we’re using the car alarm style, we’ll need a car alarm sound to go off when the boot is triggered. Thus, we decided on the audible alarm / lights flashing method.
Reviewing this brainstorming session and gaining a sense of what this project entails, I think I’m most concerned with the sound. I’ve never made sound before and my Googling has yielded mixed results. And my attempts to create sound by simply varying the frequency of a square wave sent out to a speaker made pitch accurate, yet completely unusable sounds.
Also, in order to use what’s on hand, I’m pretty sure I’m going to be using a PIC16F877A.
Let me know what you think! Leave your thoughts and comments below.