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Newbie question. I have a Davis 7852 Rain collector that measures Rainfall using a Reed switch. The output comes via an RJ11 plug with following pinout

  • Black - Unused
  • Red - Switch terminal
  • Green & Yellow- Switch terminal

I am assuming that when Rain tips the collector, a circuit is completed and a voltage output will come on these wires. My plan as of now is

  • crimp the wire - tip the switch and measure wire voltages using a multimeter
  • There would be a high voltage wire and another would be low voltage
  • Now I have to measure the difference between high voltage and low voltage wires The difference will tell if the switch has been flipped.

Does the plan look reasonable? How can I interface these wires to Arduino input pins? Any precautions in pushing the RJ11 wires to Arduino?

EDIT

EDIT-2 (in reponse to Michael)

Much Thanks. I am reading electronics text to work out this circuit :D

EDIT-3 Thanks. figured out the schematics :D

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Provide the link to the datasheet. Otherwise, your situation is unclear. –  Nick Alexeev♦ Oct 26 '13 at 18:37

1 Answer 1

up vote 2 down vote accepted

The rain collector appears to have only a reed switch contact closure output. The collector itself will not produce voltages on the wires. Instead you have to connect the reed switch contact wires into a circuit that puts a bias on the wires that can be detected by the Arduino.

Since the wires are most likely running from outdoors (wet rain location) to indoors (dry Arduino location) it is a good idea to prepare some additional protection circuitry before the input to the Arduino so that if the wires experience some electrical disturbance it does not knock out your MCU board. You could try the following circuit as a starting place to hook up the rain collector reed switch.

enter image description here

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Besides, in terms of "electrical disturbance", I can only come to think of one thing that could disturb the reading, and also potentially destroy the microcontroller, ie thunder, and in that case that circuit will do pretty much nothing anyway. I think connecting it to an IO set as an input with pullups enabled, and maybe the 150 ohm resistors and a small capacitor (100 nF-ish) between the terminals would be sufficient. –  nitro2k01 Oct 26 '13 at 20:20
    
@nitro2k01 - Your simpler circuit proposal will likely work for most cases. It will not protect the MCU very well is there is moderate coupling from nearby lightning. A direct hit by lightning will take out both circuit ideas. –  Michael Karas Oct 26 '13 at 20:27
    
Thanks a ton @MichaelKaras. I am working out the details and I have few questions. I do not think it will fit in comments box so let me update the question. –  rjha94 Oct 27 '13 at 19:00

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