Wireless switch?

[justwhy2003]

Hello Has anyone heard of a switch that can send a wireless signal to a remote alarm. Example a switched output from a PLC might apply 24 volts to the device which will send a signal to a corresponding device in a remote location within 50 metres away to activate an alarm. Its for a water tank system in a back garden that needs a high level alarm indication in the house. Thanks Justwhy2003

[Ken Moore]

Google wireless I/O, there are several makes on the market that will do exactly what you want. Most are 900Mhz, and have a line of sight range of several hundred meters. With the right combination of equipment ranges of miles are doable.

[Nathan]

Yeps, good call Ken! If that range isn't good enough, you can rig up directional antennas with boost and/or repeaters. I know there's a lot that deals with the 2.4 Ghz range, like 802.11x.

[TimWilborne]

How backyard do you want to make it? Since it is not an industrial application and seems to be more of a none critical home application, how about a plunger that raises up to hit the trigger on a wireless doorbell?

[Ken Moore]

Thats an excellant idea, industrial wireless I/O would cost near 1000.00 USD, but you can get a wireless doorbell for less than 100.00 USD. (Longer range models are available for more cost) Here's one that might work, range is 150 feet, which is near 50 meters. When you push a door bell it makes a circuit, I would think that if you carefully took it a part, you could run it through a set of dry contacts from you level sensor. http://www.gadgetshack.com/plug-in-doorbell-doorchime.html

[waterboy]

A garage door opener set would work too, they are available for even less that that.

[paulengr]

Check out Radiotronix. They are sold through Mouser (www.mouser.com). It's a "chip level" thing, but you can get into the sub $50 range for transmitter and receiver. Construction-wise, these things used an on-chip switched oscillator tank circuit (hard to explain) which means the RF filter is on-chip. With that out of the way, you literally have to apply power, signal, and antenna. If you don't like building it yourself, they will sell a kit with two transmitters (packaged in key FOB's but you can take them apart easily) and a receiver for $71.43. Saves a lot of trouble. Mouser part #509-RK-433-RC.