Next: Reverse Geocache backpack

What do you get when you stick an ATMega328, a GPS receiver, a servo control output and a button on a 2x16 LCD backpack with a battery powered step-up power supply?

Stay tuned...

Apple Magic Trackpad plugger is a go!

I got the Magic Trackpad plugger boards back from OSHPark today. The only minor change required is that it turns out that the entire inside of the battery cavity is not conductive. You have to use a stiff piece of wire and sort of jam it in the threads near the outside edge that would mate with Apple's metal plug in order to make the negative contact. So I will revise the board, moving the negative output terminal into the back corner to make that more convenient. But apart from that, it couldn't have gone better. The boards are the perfect size to center them inside the battery cavity, insuring that the positive connection will work. And the plan at the moment is to wedge a rubber test tube cork into the end of the trackpad to keep it all together. The cork will hold the negative wire in place and provide strain relief on the USB cable.

The boards will go into the store immediately. They come with the surface mount components assembled, as well as the solid core 22 AWG contact wires. You just add the chopped-off USB cable of your choice and the cork. It'll pay for itself easily in less than a year's worth of batteries!

Turning the Hydra into a two-head EVSE

It's a subject that has been broached before... What would it take to replace the inlet on a Hydra with just a straight up power cord?

It turns out it's not quite as trivial as it sounds.

The big missing item that would be required is adding a GFI circuit. The Hydra doesn't have one because the host EVSE is assumed to provide one. But having one is required by the spec (as well as being just downright prudent).

OpenEVSE includes a GFi, of course, and stealing their circuit for it would certainly be an option. The hard part is finding room on the board. The v2.2 board isn't very tight in terms of the component density, but that's deceptive - the trace density is rather high.

I could design a board that replaced the inlet management circuitry with a GFI. You certainly don't need both. But then I have two different boards - two entirely separate products, effectively. Given that I've only sold four Hydra boards so far (and two of those went to my employer), is it worth the bother?

I often feel like I'm sort of blogging in a corner by myself, unfortunately. 

SALE! Original Hydra version 1 boards in the store

I've decided to part with my old Hydra version 1 boards.

These boards were build with through-hole rather than surface mount components. All are assembled and tested. They differ from the v2 boards in that they lack a built-in display (an i2c RGB LCD display is needed for them to work and is sold separately) and they cannot perform on-demand inlet state switching like the V2 boards can.

They're on sale for half price ($50 for an assembled and tested board).

Get them while they last!

AdaFruit AD8495 breakout now available

AdaFruit now has an AD8495 breakout board now. Theirs is slightly nicer than mine, in that it has a 1.25 volt bias, meaning it can handle negative temperatures as well as positive (-250 to +750 °C for a 5 volt power supply).

It's a little bittersweet. My design wasn't novel, particularly - I took it straight from the datasheet. And they've certainly added value by adding the negative temperature range. It's also great to see a product that one championed make it into the marketplace in a (somewhat) big way, even if it's being done by someone more well heeled. But now I've got a pile of them, and nobody's going to find me once Google figures it out. C'est la vie.

Wired Magic Trackpad hack

Ok, I've decided on my next project.

At work, I have a magic trackpad for my laptop, and it's sitting right next to a USB keyboard.

A keyboard that has a USB socket on the side.

2 inches away from the trackpad.

Which eats 2 AA batteries a month.

Seriously, Apple?

A 5 volt to 3 volt LDO regulator will certainly work. The question is, how best to add it to the trackpad?

Well, OSHPark can make any size circuit board you want, of course. So how about one the exact dimensions of a pair of AA batteries? On one end, there could be a little "nub" with something conductive, like tin foil or something, connected to the positive output terminal. The other end would have a spring to push against the screw-in plug. For the negative terminal, you simply need some sort of springy metal contact that reaches either up or sideways or whatever to touch the side of the chamber.

The last challenge is how to get the USB cable in.

I've been playing with 3D printing lately. I'm thinking that the metal twist-in plug could be completely replaced with a printed plastic plug designed with a hole in the middle. The pattern for the plug would need to have the same thread around the edge as the metal one - perhaps the metal plug could be simply scanned in as a starting point.

Of course, this would only be for power - the trackpad would still use Bluetooth to communicate. But that's fine. I just want to save the hassle of changing the batteries so frequently.

J1772 Hydra boards

Well, I think the v2.2 design for the Hydra is going to be the stable design for a while. I'm not sure what to do next, though.

If I had some hope that people would actually want them, I'd place a medium run order for 20 boards. That would have a pretty substantial impact on my costs, but I have yet to sell even one Hydra to anyone.

Step right up, folks, don't be shy...