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Sensors, Actuators, and Robotics » The Long Arm of the Nerdkit

June 29, 2009
by hijohng
hijohng's Avatar

Dear All,
I was looking through the Projects page and noticed the digital meat thermometer. I thought I would pass along the following suggestion for extending the "range" of the Nerdkits platform.

What got me thinking was the photo of the meat thermometer tethered to the Nerdkits breadboard by 3 wires, maybe 2 feet long. Trying to measure the temperature of something real is probably the first thing many of us atttempt, as soon as we begin calming down from the excitement of getting that first LM34 project to work. I was constantly hauling the breadboard and associated stuff into the kitchen from the workroom. But just how far can we separate the kit from the sensors?

Quite a ways, as it turns out. And it's not that hard. I had about 30 feet of CATEGORY 5 cable (CAT5) lieing around. From a local store I bought two "inline couplers" (an inline coupler consists of 2 RJ45 jacks, mounted back-to-back, made for extending a run of CAT5 wiring) and a short patch cable. The patch cable I cut in half and stripped the insulation from 6 of the 8 wires on each exposed end. These 6 wires are now available for sensor inputs. The end of the patch with the clip-in connector plugs into one of the inline couplers. I plugged my 30-foot CAT5 cable into the other side of the inline coupler and then plugged it in turn into the second inline coupler. Finally, into that I plugged the other half of the patch cable, to which I had attached the LM34. This assembly allows me to locate my breadboard (and computer) more than 30 away from my "experiment". Here's a crude schematic:

  |------| AA  \-----/                \-----/     |----|  
  | Nerd |---+ ]CPLR [ +---{CAT5}---+ ]CPLR [ +---|LM34|  
  |------|     /-----\                /-----\     |----|

   (+-- and --+ indicate CAT5 cables with RJ45 connectors}

How much farther could I go? Not sure. I haven't tried a formal calculation of the noise in this arrangement, in decibels. But for the sensors I have, the standard deviation of the ADC output of the 30-foot version is less than 2% higher than that of the on-board version. (The noise will obviously depend on your environment.) This makes me think, for the kinds of things I'm interested in at the moment, there is no obvious practical limit.

This approach has several advantages:

   + you can locate a sensor far away from your Nerdkit breadboard.

   + the sensors never plug directly into the breadboard, only  
     into the inline couplers, which saves wear-and-tear, as well as  
     inadvertant dislocations of components.  The *breakout cable*,  
     the piece labelled AA in the diagram, is never removed from the  
     breadboard; I just plug in different sensors.

   + CAT5 and RJ45 carry 8 wires.  This means you can run two  
     3-wire sensors per cable, and still have two lines open  
     for other things.

   + CAT5, while not shielded, does have a durable plastic sheath,  
     so it is quite tough, yet still pliable enough, considering it  
     houses those 8 wires.  CAT5 uses twisted pairs, which helps cut  
     down on *antenna effect* line noise.

   + This stuff is standard, even ubiquitous, and so relatively cheap.

What are some other solutions folks have come up with?


July 06, 2009
by sgmaniac1255
sgmaniac1255's Avatar

that's interesting, and if you had "in house" cat5 you could measure the temperature or whatever sensor you're using from a separate room all together (assuming its within range)

here in my room i have a wall port just behind my computer with two RJ54 ports, they lead to the central network hub in the main computer room. in there we use patch cables to go from the wall ports to the router. in theory i could patch from one port the the other and go to another room in the house. (again, assuming the distance wasn't too far, but we ran the wires our self so i know how long they are)

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