Enigmaker

It won't help nervous fliers, sheep or paraglider pilots. It's not for dancing driven music, or a snowboarder's iPod volume control. It doesn't detect bass-thumping music. It won't help you improve your agility, your pressups or your creativity. You can't use it to draw numbers in the air It doesn't detect earthquakes or gravitation. It's not a secret-knock-detecting security device, neither will it help you break into a safe. It's not aimed at gamblers or rollercoaster riders. You can't (yet) use it to augment your iPod although this is probably a good idea. Although it's not a forehead mounted snooze detector, it could indeed help sleepy businessmen. It's not a reading aid, although it does indeed help you 'Count the stops'.

It's a....

Commuter's Friend

An alarm system to wake you up at your chosen stop on the Tube, T, Subway or other public transport system.

How does it work?

The push button selects the number of stops. It's attached by a suction cup to the window behind the commuter's seat on the tube. They place the headphones in their ears.

The accelerometer monitors the horizontal acceleration and deceleration of the train to detect stops. Each detected stop causes the countdown to reduce by one.

At the penultimate stop, the commuter is alerted by an alarm to verify the stop by looking through the window.

They can then concentrate on sleeping, reading or sticking their tongue out at passengers on the departing platform, certain that they will be alerted in time.

I've used my time machine to blog Monday's partslist for next week's #project1. More below on the design considerations for the Commuter's friend if you were to actually make a product like this, and an overview of the definitive clues from this week for the serious guessers, like the anonymous JC who guessed it, but was kind enough to obfuscate so as not to spoil it for everyone.

Design Considerations

Formfactor and barebones arduino

It is fairly straightforward to take the arduino out of an arduino project once you've finished prototyping, so that you can make the project smaller, just like the artists' impression. You can take the chip out of the arduino after programming it, and buy another to replace it. Find out about the barebones arduino at make or at fritzing. You can even do without the power regulator or crystal if a steady voltage and a steady timing precision aren't relevant to you. I haven't done this yet for #project0, but it would lead to a very slim package in the final product.

Power consumption

Powering the arduino chip at a high clock speed means more power. I don't know what the lowest clock speed is for this project to work, but I'm sure it would be able to go down quite a bit, since the sensor-sampling frequency could be relatively low. This would save power. Having a switch onboard would mean you could cut power altogether, so it would go in your pocket.

Cheaper accelerometer

The accelerometer breakout board was specified for another project and is way too capable for this scenario. A single axis analogue accelerometer would be perfectly adequate, and would be on the parts list for a productised version. Of course the breakout board itself is only needed for the hobby prototype. A final design would use pick and place and reflow to incorporate the chip directly into a bespoke board design. As you can see from the logging work I did on the prototype, a motion switch wasn't a very effective alternative, unless there's a different way to configure it (perhaps two switches set at an angle). They are incredibly cheap, so may be worth trying to find out how to make them more effective.

Suction cup

I was using a ridiculously overengineered suction cup, partly because of all the breadboards, batteries and other guff in the prototype. With the smaller form factor, productised version, I reckon the whole thing could go straight onto a cheap plastic suction cup, like the ones which stick 'baby on board' signs to the windows of 'chelsea tractors'.

Use of decimal point

If you want to have up to 19 stops, you could use the decimal point in the position of the digit one. Perhaps there are modified LED displays out there for this. After I'd done all the pin mappings for the display I realised I'd done it upside down, so the decimal point was in the wrong position to be the figure 1. Another half hour's work and you could switch the other way up.

Persistence of Vision

If you want to display multiple characters, but keep the small form factor, you can use persistence of vision, since it has an accelerometer onboard. When the accelerometer detects a significant change in direction, it can start scanning through a word forwards or backwards flashing the digits, and leaving the image of the word 'imprinted' on your retina. This could be useful if you wanted complex functions like different modes. There is almost a complete alphabet you can show on a single 7 segment display.

iPod adaptor

Finally, given this will be used with headphones, and on the tube, why not link it to your iPod or iPhone? I haven't gone looking but perhaps there's even an app for this in the store already. If you wanted to retro-fit any audio device with this, I think it would be possible to place the device inline, and have it add the alert noise to your existing music. This is left as an exercise for the guesser.

The Clues

I think maybe I made it too easy in the end. This was the clincher, especially for anyone who knows London...

Lab parked up Chelmsford tonight. Upminster's the nearest place en route to Dad's I can test #project0 for real. Have to wait until morning.

I also mentioned on the front page on the first day that I was...

fascinated by chindogu in my hobby work

...and anyone who knows their chindogo would have seen the Commuter's helmet, which is pretty close in design space.

I mentioned in commentary and tweets on the prototype circuit that the accelerometer would only be detecting in a single axis. I was also continually referring to my trip to tinker.it on the tube, and the need to visit London before Saturday. Actually if I'm nitpicking, testing mostly took place driving up and down in my camper van in the roads around Chelmsford but the principle is there.

There's of course loads more clues if you want to get into the archaeology of the project, but I have to focus on the next one now!

Epilogue

When trying to get this picture today I even found this idea and deep in the comments for that slightly ill-conceived design is one which mentions an accelerometer. I would guess that 90% of the things I come up with are already in comments at the halfbakery, which is great for public domain, although a bit frustrating for the inventor. (I always wanted an Epilogue, every since watching The Invaders as a kid).

Next week

Thanks for all the guesses this week. Some totally crazed ideas and some I might have to build one day.

If you want to try again, jump right in to the next week's project.