[ianbicking]

I always wonder with these boards why wifi isn't just built-in. It seems like a delightfully simpler interface than any wire, and means the base system can integrate with anything else over the network. Sure you can always add wifi, but the point of these boards is that they bundle all the basic stuff, and often include things like development environments that can't make use of wifi if they don't know if it is available. Power is a concern, but you can still turn it off.

[jerryr]

It's probably omitted to keep the base cost down. WiFi modules that you can get for low-quantity applications are expensive[1]. Cheaper modules generally require higher-volume consumer electronics applications--not to mention volumes of NDAs simply to get module documentation. Adding WiFi (or wireless comms of any type) also makes you an intentional radiator[2], which potentially complicates your FCC testing, adding cost and delay. So, from an MVP perspective, it makes sense to leave WiFi off if it's not critical to the base application--at least for your first revision.

[1] TI's budgetary pricing for one such module--the CC3000--is about $10: http://www.ti.com/product/cc3000

[2] http://en.wikipedia.org/wiki/Title_47_CFR_Part_15#C_-_Intent...

[ianbicking]

Thanks for those details, it makes more sense. People usually talk about the cost, which I don't buy – it's worth $10/unit, and these aren't super-low-cost units anyway. And in this case consumers of the Rex aren't going to develop something that will be the basis of thousands of units where that $10/unit cost becomes a big deal.

But I can definitely see how the regulatory overhead would be a big deal, and it seems like that regulation also makes other aspects of integration more bureaucratic. Like I bet a bunch of these chips could be used inappropriately (e.g., to emit stronger signals than are allowed) and they are using NDAs and such as an alternative to other security measures. In a sense USB wireless standards are the one interface/security layer that is well enough spec'd that it is easy to integrate.

[jerryr]

Yeah, I can see how the cost argument is borderline--it really depends upon what you value & connectivity is pretty important nowadays. But, unless the primary application is specifically "connected robots", I do think it makes sense to omit it for the first rev and get a cheaper product out faster. Don't forget that the $10 is the cost of the part itself.* You still need some support circuitry, hardware development time, software development time, testing time, etc. And then there's markup. Assuming absolute minimal costs for all of those--and direct sales with an aggressively minimal margin, I'd still expect a $10 part cost to translate to at least a $20 product cost.

* Admittedly, that $10 is budgetary pricing and would probably come down with negotiation (and there might be cheaper low-volume options--that's just one I knew of offhand). But that's likely still the order of magnitude for the quantities of the Rex.

[zhemao]

The additional marginal cost/unit is pretty low, but the non-recurring engineering cost is pretty high, even without having to deal with suppliers and the FCC. Once you've chosen a wi-fi module, where do you put it on the board? How do you make sure the radio signals don't interfere with the rest of the circuit and vice-versa? It's much easier to just get a USB wi-fi adapter and install the Linux drivers for it.

[crunchex]

Built-in WiFi was definitely on our feature-list, but you hit the nail on the head there - cost and FCC compliance were big issues. We decided to keep it simple and add it in via off-board solutions.

[lazyjones]

If you need WiFi, you could start with one of those low-cost DD-WRT/OpenWrt compatible routers ($15-20 or so: TP-Link TL-WR740N http://wiki.openwrt.org/toh/tp-link/tl-wr740n). They have little RAM, but plenty of I/O (serial, RJ45) and they're still almost "palm-size".