Friday, 26 December 2014

Wendy light mark 2!

Time for second round of the Wendy light prototype. Last time I got things going (described here), with an ugly but functioning prototype of my light based alarm clock.

Today I'm doing a second round, with more of a focus on the aesthetics and usability of the clock. While I don't expect to end up with something that looks pretty yet, I'm aiming to improve the controls and work out the basic template for the fancy looking final version.

The big change is to turn this big chunk of buttons:

Into something that looks less like an eighties arcade game, and more like an elegant alarm clock that a beautiful lady might have in her bedroom.

The plan is to replace those buttons with 3 Phidget 1129 touch sensors, and a Sharp GP2D120 infra red range finder. The touch sensors will function as on/off, reading light and alarm cancel buttons; and the sensor will replace the snooze button.

I start off using a jig saw and a router to carve out the centre of a block of pine, then cut a square sheet of plastic to sit on top of it.

There's a hole cut out for the IR sensor, but the capacative touch sensors will pick up your finger within about half a centimetre, so they can comfortably sit below the plastic.

Tip: I've spent ages trying to find the best way to cut plastic. After much testing, I've found using a Dremmel with an abrasive attachment the best bet. If you do take this approach though, make absolutely sure you wear safety goggles - it will spit small chunks of hot plastic, and some of those will head for your face. Do not get melted plastic in your eyes!

Next up, the touch sensors:

After a bit of experimentation, I removed the chunky cable attachment and soldered on my own little headers; these are less bulky, which is important now that I'm trying to fit things inside a small and more elegant box.

Tip: If you get a hold of some of these sensors, it's worth knowing they seem very sensitive to power fluctuations - mine stopped working once the IR sensor was plugged in. I shoved a big 250uF capacitor across the power terminals which seemed to fix the problem. Other than that, they work pretty well - hook up Gnd and Vcc to those of the Arduino, and the data output (white cable if you haven't remove the socket) to an IO pin, and you'll get a HIGH signal if a finger is within range.

First step for the innards is to mount all the sensors on a couple of strips of wood that'll sit inside the box:

Next, I hook up all the Vcc and Gnd pins to a little bit of strip board. This allows me to easily attach the big capacitor and connect them to the Vcc and Gnd wires that go to the Arduino (along with the data wire from each sensor):

Tip: If your circuits are ever getting too messy, connecting small chunks of circuit together on a piece of strip board like this is a really good technique. You can cut up strip board with a hack saw, or (as with the plastic) using a Dremmel with an abrasive head (though once again - safety goggles!).

Next up, as I'm wanting this to be a little neater, I'm going to stop trailing 6 wires from bed side table to floor, and instead use a Maplins 9-way data cable to connect the switch  box to the Arduino:

Data cables are a great way to keep circuitry tidy, and come in either wrapped form (as above), or as ribbon cables. However, due to the tiny wires inside they can be a little tricky to work with, so I generally end up connecting each end to normal solid core prototyping wire; this allows me to use the data cables to bridge large gaps, but still plug things into prototyping boards or Arduinos at each end.

As I'm tight on space, on the box end I'm going to solder the data cable directly to the cables coming out of the sensors (plus another 2 for Gnd and Vcc).

Soldering wires together is a bit tricky to do well, and often results in fairly delicate connections that are easily broken with an accidental tug. A much neater approach (that I used on the Arduino end) is to solder the data cable to a small piece of strip board:

As you can see, this results in a much neater and stronger connection, that can be wrapped in more insulating tape to strengthen it further. Once this is done, you can easily solder normal solid core wire or pin connectors to the other end, making it easy to plug into an Arduino or prototyping board.

A last bit of work in the shed to drill out the holes and make a cover for the base of the switch box:

Attach everything together, along with some button labels (aka masking type with my writing on):

And it's ready to hook up!

Not a lot to show in terms of actual functional changes, though I may get around to a video of me waving my hand over the sensor to snooze the alarm! Other than that:
  • I've tweaked the reading lights so the lightest setting is lighter (based on user feedback...), 
  • The central LEDs now stay dimmed for anything other than the alarm
  • The alarm cancel now triggers a small blue pulse effect, similar to the red/green ones for on/off. This is just to give some confirmation that the touch button worked.
So generally happy with prototype number 2. Final version will be fairly similar I think. The box itself I'll probably make out of white oak, then stain the same colour as the wood the bed is made of. Plus of course I'll have to make a proper box for my side of the bed too! Then a less fancy box for the Arduino under the bed; the LEDs fixed behind the wall; probably some small side buttons so you can set the alarm time and things; Printed button labels (ideally glow-in-the-dark). That should just about round off the Wendy light!


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