Aurac

I want to make 2x arduino talk to each other via rf and using sensors. If 1x arduino detects an obstacle it sends a signal to another arduino to lyt a red lyt, if the first arduino area is clear it sends a signal to the 2x arduino to switch the red lyt to green. This is to be used in a railway station, were arduino 1 is in the station arduino 2 is on the approach to the station, if 1 has a train then 2 is red, if no train in 1 area then 2 can proceed to station. I hope that is understandable to you. Plz try to help. [email protected]

I need to make a car battery monitor using the LM3914 ic. led 1 = 10v, led 10 = 13.8v what value resistors do I need? i have a full stock of resistor values, 2x LM3914'S and 2x 10 led bar graph displays, but cant experiment and blow an IC. I also have a good range of capacitors, diodes etc.

I need to have led 10 at 13.8v led 1 at 10.0v what resistor values will I need?