The need: I have a wireless ADSL connection, with an antenna placed on my roof. This antenna is always turned on, even when my home network is off. So I decided to build a proof of concept device to turn on or off this antenna with a relay, by looking for the presence of my SSID on the air. In this way, when I turn off my wireless router, the antenna is switched of as well.
On the other side, when I switch on my router, the antenna is turned on again, letting me on internet again.
The concept is quite easy: when the module see my SSID on the air, it turns on a bistable relay, when it does not see any more, it turns the relay off.
I choose to use a bistable relay because it does not need current to hold the position set. So if the power go away, the position is maintained (and also it consume less current).
The realization is quite simple. Two PINs of the Linkit ONE control the status of the relay. Since the Linkit ONE does not provide enough current to the PIN to drive a relay (as it is stated in the documentation), I used a couple of transistor to create the circuit needed:
The connection to the latching relay is quite simple. It has 4 PINs:
Set and Reset can receive a signal from the LinkitONE. When using voltages over 3v never hold SET or RESET for longer than 1/2 second, shorter if possible.