Beth over at scanlime is no stranger to building electronics. But this time she wanted to, well…in her own words, “create something new and exciting that I can immediately use in my everyday life. It also happens to be a sex toy.” Specifically, one of those little remote-controlled vibrating egg things.
She ended up producing a hack that is remarkably polished. She even designed and 3D printed a custom enclosure for the whole thing. If she had used neon pink plastic it would have been hard to tell that it wasn’t part of the original product.
She’s got an incredibly detailed description of the project on her blog. Personally, I think the most interesting part of the hack was her solution to the power problem.
This was getting complicated fast. Lithium polymer battery, a boost converter to raise the voltage to 5V for the sonar module, charging circuit, “fuel gauge” indicator. All of this work goes into every commercial product that runs on batteries, and we often take it for granted. As far as I’m aware, though, there isn’t a great equivalent for quick DIY prototyping. The Arduino Fio board is close to what I want: an Arduino with a built-in LiPo battery charger. But it doesn’t have the 5V boost converter or any way of monitoring the battery’s charge. Without designing my own PCB, I’d need several separate components: battery, fuel gauge, charge/boost. All total, over $45 and a lot more bulk and complexity than I wanted. I was really hoping there was a better option.
It so happens that this sort of amalgamation of parts is already pretty commonplace in the form of portable cell-phone chargers. These devices are very little more than a boost converter, charger, lithium battery, and a very basic fuel gauge. Best of all, thanks to economy of scale, they’re really inexpensive. The 3200 mAH battery I used in this project was only $22, and it’s something I can reuse for multiple projects… or even to charge my phone.
This is an elegant solution that can apply to an array of different projects. Once something becomes commoditized it can drop below the price point at which it makes sense to reproduce the functionality yourself. All wireless projects need power, and with cell phone chargers becoming cheap and easy to find it makes sense to just plug one into the project’s USB slot and call it a day. Not only is it cheaper and easier, but it’s modular because you can still use it for its original purpose.