SparkFun Forums

[rdg-123]

I'm sorry for not being clearer...my common wires are all white and the bundle of station wires are genereally all red. So I know at every point which is my common and it spiders to every manifold in the system.

The more information I have, the crazier this project seems. I have a multi-trunking common that runs everywhere with multiple stubs going all over. The electrical weight of 3000' of wire is probably a great obstacle to overcome.

At this point, I'm thinking of just using a sender unit that can know what station it is supposed to be (1-99) that can be triggered by an Xbee master unit which will then be able to read which wire just turned on, probably by lighting an LED. The cost is greater, but the prototyping will be easier (he says knowing nothing of XBee and Arduino programming).

I really appreciate everyone's help.

[itsthemedication]

"I know I can run differing levels of power with resistor leveling, but this has some limitations for "transferring" the technology to my crew. They could read a number from an LCD panel, but might not get the idea of differing voltages on a multi-meter."

Create an interface in the control station that consists of a an arduino with a hefty megaohm resistors for impedance isolation, and read the varying voltages coming back from the valves. For any given voltage, the arduino will display the associated valve number. You are essentially creating a "dumbed down/specially crafted" multimeter using the arduino analog input ports, and the arduino is left in a relatively safe environment. I've seen alarm systems that work on this principle. They use different resistor values to set a voltage in a multiple sensor loop that is identifiable by the alarm controller. There are multiple resistors for one loop, and when the sensor goes into alarm, the resistor for that sensor is shorted, so the sum (can be a parallel, ladder like system as well) of the remaining resistors left in the circuit determines the voltage that allows the system to determine what sensor actually tripped. I think for what you are doing, you need a rugged, dumb sensor at each end point, not a delicate system spewing back serial communications.

Be careful! Electricity and grounded copper pipes is a recipe for electrocution, but I'm sure your well aware of that.

[rdg-123]

Not too worried about electro-shock aversion therapy. The 18v battery shouldn't send too much my way. Not interested in hooking up to line voltage, so...

Would there be an easy way to setup the resistors in some sort of selector circuit, so I could dial in the "station-voltage" that would signal a number to a pre-programmed arduino, or, would the circuit need to be calibrated each time? I'd love to be able to set up a voltage chart in my arduino and be able to reliably "dial up" a station number.

[rdg-123]

http://www.sparkfun.com/commerce/produc ... ts_id=9185

Am I reinventing the wheel?

[bobcousins]

If I understand this, you want to avoid a lot of walking around. Therefore, you want to attach a Tx device at each remote station, then be able to attach a Rx unit to each wire at the control box and read off its ID from a display.

I think this could be achieved by sending an ID using RS485 over 2 wires, although I would check this with a sample of cable first. Bit rate could be as low as 300 baud since you only need one byte of data to hold the id. I'm not sure which Arduino you have, but you will need a TTL to RS485 converter. There are cheap ICs to do this, but packaged solutions tend to be expensive. Sparkfun have an adaptor that might be suitable, but it's hard to tell from the limited spec.

This method would be a bit expensive if you want to hook up 40 stations at once, but maybe you could do say 10 at a time.

[Franky]

Not sure if I understand your setup correctly, but you might be able to use a RS232 repeater instead of converting it to RS485. Some RS232 repeaters works up to 2000 feet and will even isolate your interfaces. Or as earlier mentioned here wireless might be more relevant. A couple of wireless RF modules might do the job. This RS232 to RS485 converter wiki i a good reference, it much easier to find out what you need inf you are sure about the basics.