Affordable sensors


(Richard Lee) #1

Why are there no affordable zigbee/zwave sensors or switches on the market? The Iris stuff from Lowes comes close, except that they have crippled it for some reason with proprietary protocols (i suspect marketing is to blame, not engineering). I costed out the parts on Digikey and Mouser. At volume, it doesn’t seem like these things should cost more than $10-20 each to make. Seems like people are raking in a lot of margin?

On principle, I’m inclined to just build my own from scratch, even though the hours I’d spend doing so will cost far, far more than the parts. And they probably won’t look as nice. Maybe we should start some open sensor design sharing? I mean, get something like this:

http://ww1.microchip.com/downloads/en/DeviceDoc/70329b.pdf

comes WITH a trace antenna for $10 each (no volume), pair it with a basic Atmel AVR microcontroller for a few bucks, add another couple of bucks for extraneous caps and resistors, battery clips/voltage regulator and such, write up a communication library to make talking to the zigbee chip sane, and you have the foundation for any sort of sensor/controller you’d like. For a bit more money, $17, you could get a much more powerful transmitter:

http://ww1.microchip.com/downloads/en/DeviceDoc/70599B.pdf

Hell, Atmel even makes an integrated AVR+Zigbee chip for less than $8 each.

http://www.atmel.com/Images/Atmel-42073-MCU_Wireless-ATmega2564RFR2-ATmega1284RFR2-ATmega644RFR2_Summary_Datasheet.pdf

However, it has no integrated antenna, and antennas are a bit of EE black magic I’d personally rather not deal with. Tho, maybe if someone here understands trace antenna design, that could be made to work, too.

Then the marginal cost is just in the sensors. A PIR is about $10-15, accelerometers are a few bucks. hall effect magnetic sensors are less than $2. Thermistors are super cheap. A relay for switching mains power is probably around $5-10.

So, smartthings, what’s up with the ~$50 cost?


(Col Hack) #2

You’re right. I can buy 6-axis accel/gyro board on eBay for two bucks and Nordic radio board for another $1.50. And that’s with shipping, single unit volume. Add TI low-power MSP430 micro for 50 cents. There you have it - four buck worth of parts. In large volumes should be even less. Granted, it’s not Zigbee, but who cares? Door/window and motion sensor as well as key fobs are pretty dumb and only need one way communication link anyway. Fifty bucks for a motion or door sensor is a ripoff, Zigbee notwithstanding.