Temp sensor breakout box idea

[Nofossil]

I'm interested in how people are dealing with all the cabling that goes with temperature sensors. I've got a dozen sensors and I'll be adding more. The cabling is something of a disaster.

Part of the problem is that I'm measuring temperatures at points that are pretty far away, and I don't want to run a cable back from each sensor all the way to the controller.

Here's the best that I've been able to come up with so far. I'm eager to see what other ideas are out there....

I'm testing out the idea of a remote 'breakout box' that has a single cable going to the controller but supports up to four sensors. I'm using standard network cable with RJ45 connectors to go from the breakout box to the controller, and I'm using standard phone hookup wire with RJ11 jacks for the sensor leads.

The sensor in this photo is an LM35. The miniature circuit board in the cable has a couple of caps and a resistor that are necessary for long cable runs. The circuit board will be dipped in plasti-dip goo (the stuff that you dip tool handles in).

Rough costs:

Sensor , caps, resistor: $4
Phone cable: $0.01/ft (at Big Lots)
RJ11 plugs: $0.50
RJ11 jacks: $2
RJ45 jacks: $2
Cover panel: $2
Outlet box: $2


Total material cost for breakout box is about $6, and each sensor/cable assembly is about $7. This doesn't count the miniature circuit board which I made by cutting up an old protoboard.

 

[Adabiviak]

How long are those runs? I'm not familiar with your temperature system, but does that just funnel the wires to the controller? There are Bluetooth serial dongles (requires power at the point though), and if the information is analog, you'll need to deal with translating this. Bluetooth is typically only good up to ~30' without obstructions, and there are other RF solutions that could probably cover your whole house. How is the information transmitted from the probes to the controller? (analog voltage level, RS232, RS485, etc.)?

 

[Nofossil]

How long are those runs? I'm not familiar with your temperature system, but does that just funnel the wires to the controller? There are Bluetooth serial dongles (requires power at the point though), and if the information is analog, you'll need to deal with translating this. Bluetooth is typically only good up to ~30' without obstructions, and there are other RF solutions that could probably cover your whole house. How is the information transmitted from the probes to the controller? (analog voltage level, RS232, RS485, etc.)?

My sensors are up to 50 feet away from the controller, and many are outdoors and/or submersed in a sensor well inside a tank. This scheme is completely passive and analog. The goal is to get multiple analog signals back to the analog inputs on the controller at minimum cost and aggravation. In a system with 16 analog inputs, I'd like to avoid running 16 cables all the way back to the controller.

I've looked at RF, but as you point out you have to run power out to the sensor anyway. I've had real problems with interference as well - doesn't seem to be a robust approach, at least with the sensors I've tried.

These signals are in the range of 0V to 2.5V and come from LM35 sensors, thermistors, or thermocouple amplifiers. For hydronic system temperature ranges, they give me a resolution better than 0.1 degrees F and an accuracy of about +/- 1 degree before calibration.

I'm also taking a personal challenge to create a system with high performance, extremely high reliability, low power consumption, and the lowest practical cost. Right now I'm looking at a total cost for materials of something like $20 per channel (in sets of 8 channels) for everything including the sensors, cables, connectors, and interface board in the controller.

If there are better approaches, this would be a great time to share ideas.

 

[WoodNotOil]

I am planning on using the DS18S20+ 1-wire digital thermometers (free samples at http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2815/t/or) hooked up to an arduino usb board (http://www.arduino.cc/). I will have the arduino board in a box near my computer and run 6-wire telephone wire (50' for $6) from the arduino to a box down by my heating system. All of the DS18S20 thermometers will communicate over 1-wire (thus the name), ground through another wire, and 1 wire for the output that will control a solid state relay to turn my storage charging pump on and off. This leaves me ultimate flexibility to add more thermometers or relays and makes the arduino board more useful since all of the inputs don't have to be used up on sensors and allows me to have more outputs to possibly control more pumps or valves in the future. So far I have $65 total into this for the arduino board, a resistor, a solid state relay, wire, breadboard, a plastic box for the arduino board, and shipping. I still have to get a metal box to house the relay, but that seems like a good price to me! The parts are on the way in the mail and hopefully I can get it up a working soon to let others know how it goes.

 

[termite]

I'm using Adam modules from Advantech. You can find them on ebay for a reasonable price if you are patient ($100 +/- for thermocouple modules, usually less for digital and analog in and out). They communicate via rs485. If you are hardwired to your boiler room and good with VB you are set.

You will need an rs232 to rs485 converter to connect as many as 255 of them to your computer using an unused pair in your cat5. I'm running both rs485 and network in the same cable. There are other rs485 connectivity options including wireless and virtual serial ports via tcp-ip adaptors. It's not the cheapest option but if, like me, you lack nofossil's skill set it may be an option to consider.

Right now I'm using a module for 8 thermocouples, a digital input module to watch the pump states (pump icons turn red if pump is off), and an analog input for the output of the lambda sensor controller. The lambda sensor is not being used in the screen capture.

I have plans to implement automatic control of the primary and secondary shutters and/or two separate fans to keep optimum excess air throughout the burn, as well as a host of other automation and control scenarios using these modules.

 

[free75degrees]

Here's a picture of my control system. I just added the green temp sensor connection board. It provides 16 ds18s20 temp sensor connections, each one gets a dedicated i/o on a dio24 board. As you can see, I haven't hooked up the sensors to this new connection board yet. The sensors that are currently in use connect to the yellow board on the top left (ethernet cable that carries 4 sensor signals. Eventually I will have my tank sensors, tarm in and out sensors, outside temp sensor, and one sensor replacing each thermostat for the 4 zones in my house. The thermostat cabling will just utilize the thermostat wire that is already in place - I'll just swap each thermostat with a ds18s20 and move the basement connection from the taco relay board to my green board in the photo.