Thursday, September 25, 2014


I've been looking for a while for a better option than the XBee for theatrical use. The XBee modules are fantastically easy to use -- basically, they are the Arduino of the wireless world. But they are also expensive. Even eBay sellers can't get you below $20 a unit.

The other downside is indoors range. The higher the frequency, the worse the reflections, and the 1mw standard XBee can't reliably get from one room of my apartment to the other. And you can't count on having good line-of-sight in theater. The XBee "pro" model increases this output power substantially, and can brute-force a signal all the way from booth, across the stage, and into the dressing rooms (which I've verified by using it in actual performances). But this option is also costly, raising the price per module to nearly $50.

The trouble with finding wireless options for theater is the combination of range and necessary reliability. We can't afford dropped signal if that is triggering a key effect. And the majority of bluetooth data links down to cheap keyfob transmitters are designed to operate at, maybe, 25 feet.

Well, there is a series of modules out there. The RFM69 series from HopeRF are under ten bucks each, even for the 100mw RFM69HW model. There are even (nascent) Arduino libraries for these increasingly popular modules. They do lack the ease of use and existing infrastructure of the XBee, but this seem the better choice.

The combination of high power and low frequency makes for better indoors range. And the low unit cost means I can incorporate remote control as a viable option to the DuckLite.

I've been looking a lot at parts costs, and with Chinese RGB modules, the cheaper MOSFETs for power switching, and ATtiny chips -- or, at least, using ICSP headers instead of incorporating a USB option -- I can get the unit price down to not much over $10 a light module. This makes it plausible to use them in multiples in a stage production; to have a set of lanterns or party lights or tea lights or costume lights or whatever.

The downside was going to be that the cost of controlling them remotely was going to be prohibitive, enough it was almost not worth adding the option even as an unpopulated set of headers. But with these nodes, this might return to being a viable option. With the realities of interface, power management, CPU support, physical headers, and so on they should roughly double the price of the modules, but this still seems plausible.

It also means all the work I've done so far in laying out the new PCB is a waste. Back to the drawing board on that one!

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