[Noisebridge-discuss] Wireless relays + sensors

[Jake]

Hi Carlo,

I recommend the arduino platform.  It is pretty easy to code in arduino's 
flavor of C (basically just like regular C except less pedantic) and the 
hardware has all the things you need.  Six analog inputs and 13 GPIO 
General Purpose Input/Output pins.

If you're going to be controlling things running off of DC power, you can 
simply use an N-channel FET connected between the output pin of the 
arduino, Ground, and the minus terminal of your pump or motor or whatever.

If you're going to control things powered by 120V (or 240V) AC power, you 
need an opto-isolated SCR relay, or if you prefer you could use a regular 
coil-style relay.  If you use the former, you just connect it to the 
arduino output in and arduino ground, and the other side of it has two 
screw terminals that go in series with the AC load.  Very simple and you 
could control a 5KW water heater if you wanted to.

As for sensors, to use a thermistor temperature-sensor you just wire it to 
one of the six analog inputs with a pull-up resistor, and read the value 
in software.  There are also digital and analog temperature sensors you 
can get from mouser or digikey which require no calibration and send 
temperatures in numbers of degrees either through digital protocols or by 
sending a DC voltage to your ADC.

I can't see why you would need a raspberry pi for this unless you needed a 
web interface.  If you did, I would recommend considering the WR-703N 
which is smaller than a raspberry pi, half the price, and has a 500mW wifi 
radio built in.  And it has GPIO pins you can use to control stuff, 
although it would be easier to just plug an arduino into its USB port.

-jake

Carlo wrote:
I bet something similar has already been discussed :) but...

I want to control a few water pumps (low power, aquarium kind of
pumps) via software, and read inputs from a sensor or two (humidity,
temperature).

I'd like a solution that is cheap, I can bring up as quickly as
possible with as little work as possible, ideally no to little
soldering, I can easily program with good libraries (python / C /
whatever is fine). Eg, I'd like this to be a one afternoon project, I
plan to get most of my hacking fun by playing with the result, rather
than with building the system :)

I was looking into:
1) raspberry PI + relay board + sensors.
2) Arduino + relay board + sensors - seems like a bit more work than
the above? even if more flexible?
3) Something like:
http://www.controlanything.com/Relay/Relay/WIFI_PROXR&CpField=relays&CpValue=4
they seem to have tons of pre-made relatively low effort solutions.

I've had some embedded experience in the past, but have not used any
of the above. Suggestions? hints? experiences?

Thanks!
Carlo