I accidentally deleted one of Nitin’s comments before it got approved, this was a response to one of my posts about hardware, musing about USB, Ethernet, and how much autonomy a device should have:

“Did you get a chance to look at my imgizmos site?
I basically went USB and offloaded all intelligence to the PC.
In fact the USB device only operates a relay based on the PCs commands.
The PC gets its command from yahoo IM.
What I am getting at is that a device connected to a PC needs to have very little intelligence since the PC is way more powerful.
You probably only need smarts in the device if it is not always connected (in which case it cant bring in twitter/I messages anyways).”

Thanks for the comment, Nitin.  I used the power of the PC for the past couple of years (via USB), but have since decided that independence from it is a very good idea.  More and more people are moving to laptops as their primary PC, which are on standby when not in use.  And there is a trend toward no PC at all in several people I know!  iPhone, Blackberry, these are enough for them.  So not even any home internet connection.

The Ethernet idea is based on the assumptions that many people have high-speed internet connections at home, and that modern routers have more than one Ethernet jack.  So a little custom gateway, using the one-way method I discuss elsewhere, is the simplest thing I can think of.

But I have also looked at a Bluetooth-cellular-internet path through smart phones.  This wouldn’t be bad, if more people had data plans, and writing gateway apps for phone OS’s didn’t have so many wireless-vendor-imposed security barriers, and Bluetooth had better range, and making BT connections wasn’t such a headache!

Radio addressing

Use the mesh networking capabilities of the Zigbee radio, but use some proprietary protocol so I don’t have interoperability requirements with Zigbee devices and networks.  Second key advantage: no need to buy a block of addresses from the Zigbee people.  Finally, I can create my own addressing system, and can sell blocks or individual addresses to experimenters wanting to make their own devices for the network.

Ethernet addressing

I don’t see any way around this.   I think I am simply going to have to buy a block.  I have two interesting options if I do: first, as I don’t plan to interoperate with Zigbee, and if I end up putting ethernet on every device, I can use the MAC address for the radio system.  Second, I can sell MAC addresses to other people who want to make aiosphere-compatible devices to sell.

So now I need to decide:

Hardware addresses

Do I need to buy a MAC address block? Do I need to buy an IEEE address block? Is there any way I can do without either one? The experimenter community should buy a block of each and sell them off in small amounts. Also, they seem redundant. When I have a device with ethernet and zigbee both, I have two nearly identical 64bit addresses. Both expensive, too!

Core component makeup

I also need to decide between a highly-integrated solution (like ConnectOne for Internet and and TI for Zigbee) and something I roll myself using cheap Microsoft parts. My choices now are:

1. Microchip Ethernet controller for the Ethernet solution. Lowest cost I think.
2. Wiznet for the Ethernet solution. Probably most robust, lower code overhead.
3. ConnectOne would be even more robust and simpler (includes DHCP, keepalive, etc), but it would be more expensive.
4. TI would likely be the most robust, lowest code overhead Zigbee solution, but it would be the most expensive.
5. Microchip would probably be the cheapest Zigbee solution, but it would require a micro to hold the stack and do all the work. If I’m lucky, the Zigbee stack could fit in the same micro with the Ethernet stack.

Module first draft

Should I do a very quick first draft using modules? If so, are there any that offer a path to a custom component-level solution?  I doubt it.  I probably need to break down and admit the same thing that everyone else has: that the Digi-style smart ethernet connector, and the Xbee, are the best way to go for prototyping and even small volume production.  About $50 parts cost, or about $80 my sale price for one-off production.

If I go this route, I clearly will NOT make a single design for gateway and devices.