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Hardware Question


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#1 JeWill


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Posted 30 January 2015 - 01:36 PM

Hi - I'm very new to electronics - I'm a software person - so that part is not so scary to me - but I love the idea of embedded systems -   I have been studying the electronics side - but there's a lot to learn - Anyway -


I have a Netduino Plus 2 - and I have a driveway alarm (Dakota Alert Receiver) WR-3000.    The Dakota alert has a Relay for 4 ports  - each relay having an NC,NO, and COM wire connection.   


The ports on my receiver have a Driveway sensor on one - and a motion detector on another - so I have two IO's that I want to monitor.   The driveway alarm fires when a car is about 600 ft away - and the motion detector fires when a car or a deer is about 80 ft away.   Which is great - but I don't really care about the motion unless the driveway alarm fires first...  so I need some logic in there somehow.  Right now - both alarms go off all of the time for every event - which is not real practical.


The Relay specs are 24VDC 3a  (which I don't really understand because the receiver is powered by a 12VDC power supply)  


I want to set an interrupt on each relay when it goes hot - and trigger an event.   So - unlike everything I've found online in dealing with relays - mine happens to be an INPUT.    


I've calculated the Voltage Divider - that a 4.2k ohm and 1k ohm resistors will drop the 24VDC down to 4.21 - is that ok? 


But my big question is - how do I wire up to the Netduino?    If I use a Voltage Divider circuit - I can bring the voltage down to between 3.3 and 5 v - but ....   do I just connect the NO wire (after the 4.2k ohm resistor) to a GPIO port?   But where do I complete that circuit (after the 1k ohm resistor) on the Netduino?   And do I need to wire up the COM on the relay to somewhere on the Netduino?   And since - I have two of these - can I combine the COM into one hookup on the Netduino?


Thanks much for any input. 

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