Can I connect the N/O pin ( 12.8 V when relay on ) to the Arduino input pin using a resistor ?If so, is my guess of a 390 ohm resistor correct ? ( 12.8V to 5V 20mA )
My (very limited) thinking was that, just as a resistor would reduce the power for a LED, so it could also reduce the power for an input pin.
Do you have a diagram or link for a voltage divider for this type of application ? All I need to know is when the external relay is powered - that is, when there is 12.8V on the NO contact.
Use something relatively large, but not extremely large like 5K for Z1 and 10K for Z2.http://www.raltron.com/cust/tools/voltage_divider.asp
Looking at the calculator, if I put R1 = 5000 and R2 = 10000 then the output voltage is 8.533 -- wouldn't this kill my Arduino ?
If I switch the 5k and 10k around, it shows 4.267 output volt.