All,
I'm new to this site so I hope you guys can help me.

What I'm looking to do:
I am buying a PLC which I plan to mount in a remote location(possibly garage). I am planning on controlling a lot of things but the first project is Fish Tank related stuff. So ... Without going into details I have a float switch that is on/off and I want to connect that to an RF Transmitter and put the receiver on a relay at the PLC. That way when the Float triggers it triggers the relay at the PLC and in turn triggers an input to the PLC.

Float Switch --> RF Transmitter --> RF Receiver --> PLC Input --> etc ...

So ... that is what I want to do ... Here is my thought process. Ebay/Amazon/etc sell these multi-channel RF relay controls. I was looking at an 8 channel one to control up to 8 different on/off signals from the fish tank area. I'm fine with all of that ... The Question is ... I would need to remove the button and wire the Switch across the button contacts.


Has anyone torn one of these apart and have an idea of how I could wire my switch contacts? Or is there an alternate product available that I could wire in the switch? What I want to avoid is having to do all of the programming to connect the RX and TX modules.

Any thoughts?

 

One comment I want to make before you get really started is that the cheap devices are prone to interference and if something could go wrong, I'd consider some other technology like Ethernet/WIFI/Rs485 or even a DXS alarm transmitter.

An Opto FET will generally work across a button.

 

One comment I want to make before you get really started is that the cheap devices are prone to interference and if something could go wrong, I'd consider some other technology like Ethernet/WIFI/Rs485 or even a DXS alarm transmitter.

An Opto FET will generally work across a button.

So ... I'm good with the idea of reliability ... Do you have an idea for an existing product that would need minimal changes?

Another note ... I am not planning on latching the output. As soon as the signal stops transmitting the relay will be off. I may program the PLC to make sure not to switch the output more than every couple seconds or something ... but no more than that.


Ideas?

P.S. The idea is to keep it cheap so I can put this type of device in multiple locations throughout the house without driving up the cost. Also to avoid wiring all of the inputs directly to the PLC.

 

I see this for a Wifi Relay Receiver ... But how could I control the signals using the switches I mentioned in my original post? Obviously I'd have to create some sort of Wifi Transmitter with Switch inputs ...

Thoughts?

Wifi Relay:
http://www.sainsmart.com/sainsmart-...?kpid=718_en&gclid=CMOj3rWCg8YCFcE2aQodnxIA-Q

 

I'll look at what you said later.

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Remember that the usual way for transmit/receive to work is that it's one way and the inputs are momentary. Generally it's not meant to continuously transmit. For reliability sake, it your trying to use a wireless transmitter for things like auto fill of a tank, don't even think about it.

I'm planning to set up one of these http://www.homecontrols.com/Linear-Supervised-DXS-Format-RF-Receiver-LNDXSR150 in 8 channel mode. The transmitters are expensive. With the proper transmitter they can have a "ping" type signal enabled to verify the transmitter is alive. It also has a low-battery signal available. Some of the transmitters are totally waterproof andd a new transmitter must be purchased when the battery dies. These are used in wireless alarm systems where false alarms are not a good thing. I've had one transmitter and medical alarm receiver running for about 8 years now.

My plan eventually is to integrate:
1) A wireless doorbell - hacking an xmitter with a dead battery.
2) A wireless motion detector - for activation of a water re-circulator in a bathroom

Not sure what else yet.

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For PLC type stuff, you should look into MODBUS type stuff. Modbus runs under RS-485 (a multi-slave serial protocol) and Ethernet.

With Ethernet you can use repeaters in a different mode where the system uses the wireless signal and creates a wired network, so "fish tank" converts the wifi signal to a local wired Ethernet and the PLC could actually do the same.

Remember, I don;t want to actually suggest anything, but rather suggest ares that need some sort of education. I'd look here too.

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You may have put the cart before the horse too. i.e. selected a controller before the requirements are known.

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In the process control world, you will find redundant ring ethernet hubs and not being shared with the the IT stuff.

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I once tried to convince the powers that be that a network system was the way to go. This was when PC and MAC had slots and there was no USB. I was voted down. So, we ended up with a Mac running card interfaces and Labview. This was a time when selections were somewhat slim and grim. The Mac II era. and USB didn;t exist.
The good part would be that probably because of the way I wired stuff, moving to a bus based system or PLC would have probably been reasonably easy.

Other systems I was involved in went with IEEE-488 and therefore were easier to upgrade.

Another upgrade I suggested was shot down by management and later approved some 17 years later.

 

Well ... Damn ... Lol ...

All that being said it might just be easier/more reliable to run the wires for this fish tank project.

I did not actually order the plc at this point but am planning an Allen Bradley micrologix 1100 series ...

I think I'll buy a premade remote relay and test it's reliability ... If the momentary contact works reliably I can do logic at the plc to turn the pump on for a certain amapunt of time ...

So .. I really appreciate your comments and I'll likely plan to just run the wiring(dread) and use the wireless as a fun tool to test until I can determine its reliability...


Thanks again ...

 

Once you get to MODBUS, a lot of options open up for you. See http://www.redlion.net/rtus-io-modules/ethertrak-2-io-modules as an example. Then your I/O gets to be distributed.