RJ-45 jack and 6 sensors.

I am working on a wiring scheme for doing a little perf board with several sensors. The perf board will connect to an Arduino by using RJ-45 jacks and an ethernet cable.

The first use is for a refrigerator door open logging project. I am studying the impact of opening the refrigerator door on energy use. The Arduino will be 20 feet away and plugged into a computer.

Here is the pinout so far

  • Pin 1 +5 volts through 110 ohm current limiter
    Pin 2 Thermistor 1. Between 5K resistor tied high and 3k thermistor.
    Pin 3 Thermistor 2
    Pin 4 High side of normally open Switch1 in series with current limiter.
    Pin 5 High side of LED1 with current limiter to ground
    Pin 6 High side of LED2 with current limiter to ground
    Pin 7 High side of Switch 2
    Pin 8 Ground Common for 6 devices above.


Not sure what you are asking but it looks OK to me.

Being pedantic it's not perfect as you are using the same ground for LEDs an analogue measuring but given the number of pins you have and what you want to do I don't foresee any difficulty.

Best of luck with it.

P.S. I bought a fridge about 5 years ago and it made a big point about:- 1) The large lips on the trays prevented cold air escaping when the door was opened. 2) Correctly stacking the contents so as not to "wrong shelve" frequently used items.

(it was German :) )

Thanks for the observation about problem with LED and analog sensors sharing the same ground.

I am going to drop one LED and use the resulting wire to ground the thermistor sensors.

Another design thing I am trying to keep in mind is to arrange the signals on the RJ45 so the Arduino will not be damaged if a passive cable continuity tester is plugged into the sensor end.

I use a gadget where each pair of the 4 ethernet wire pairs is shorted. I use it with an ohmeter to find miswired plugs.

I hope to arrange the signals so the Arduino will not be damaged if I attach this gadget to the end of the sensor cable. I could use the Arduino to test the connection cable itself.

I'm not suggesting you redesign your project but it sounds like the perfect application for Dallas one-wire temperature sensors (DS1850) and addressable switches (DS2413).