Glitch and the LED Sneakers: Epilogue

What now?

Well, it was a one-off… a little bit of fun for the Glitch Launch Party and an excuse for me to explore the Arduino platform. However I just noticed today that the in-game shoes have a couple more tricks up their sleeves (do shoes have sleeves?). When you’re away from the keyboard in the game and your Glitch falls asleep, the shoes pulse gently in time with your breathing. Also when you laugh or frown, the lights have their own emotions that mirror your character’s. This got me thinking about ways to extend the project.

One possible project might be to add the control button back into the system – pressing that would override the current effect for a limited amount of time to show an “emotional” effect. Maybe press once for laughing, twice rapidly for angry, three times for sleeping.

Another project might be to explore analogue control of the lights to allow a fading pattern. The Lilypad supports analogue out using a Pulse Width Modulation technique (ie it turns the pin on & off rapidly… more on than off means brighter, more off than on means dimmer) – but the built-in support only works with 6 of the I/O pins so I’d have to investigate controlling the rapid on/off cycling myself.

Another project might be to add some sort of sensor to the system… maybe a resistive chest strap so it can tell my breathing pattern, or a thermo sensor so it can detect my temperature. The board could then alter the light patterns automatically to represent some aspect of my physical state.

What Went Wrong

In general the project went off really really smoothly. From both an electrical and software point of view it was very simple but I know that simple doesn’t always mean free of frustrating faults. I had no significant issues with either the electronics or the software, just a couple of minor niggles.

One ‘gotcha’ was that the USB connection to the computer had to be wiggled just-so or else I would get power but no data to the Lilypad. At this point the Arduino software would see no serial port and fail to download to the board. Having hit this a couple of times I learnt how to spot it and wiggle the cable successfully.

Another hiccup was the power consumption with multiple LEDs on simultaneously. During initial testing with a single AAA cell, I found, at idle, the Lilypad was drawing about 9mA from the power supply board. With 2 LEDs on per side (4 total) that rose to 93mA. Because of the way the step-up electronics work, that worked out at 230mA from the actual cell. If I tried to turn on more LEDs the cell couldn’t supply enough current and the Lilypad reset. I minimised the peak battery loading by careful construction of the flashing patterns to alternate the shoes on/off cycles but I replaced the single AAA cell with a three pack for extra safety. Reading the datasheet for the NCP1400A voltage converter chip says the chip has a 100mA maximum output current so I think I was lucky to be able to get as much out of it as I did.

What Would I Do Differently

There were a couple of things that I’d do differently if I did the project over again.

First, I’d take into account the way that the straps sat on the shoes before I glued the LED ribs on to them. The stretchy straps lean slightly forwards because of the slope of the shoe – I didn’t think of this and I glued the LED ribs onto them at right angles and so they’re on a slope rather than being parallel to the ground. If I’d tried the shoes and straps on first, before I got the glue gun out, I could have glued the LED ribs on at an angle so they remained flush and level to the ground.

Secondly, I’d choose a different power supply. There’s some really nice Lithium Polymer batteries available, supplying 3.7v with a capacity of 1000mAh or more. The power supply board for this is electrically almost identical to the AAA board, the only addition being an over-current protector – which might actually be overkill as the NCP1400A has a 350mA current limiter built-in. I think this would have been a little neater than my contraption with the 3xAAA cells. Although, given that I didn’t have to buy a separate charger, or a battery, the solution I ran with was actually cheaper and more flexible.

 

All in all, a great success and I’m looking forward to having some more fun with Arduino (Lilypad or otherwise) in the future – as soon as I can think of another excuse!

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