LED control

Other Hardware LEDs and Multiplexing
1

Evening all,

I have a project (theory) that I need a little help with. So i have a source that uses 18-19.5 VAC that is going to use the ground to trip a relay that is operated with a min. 8 VDC. Im then going to use that 8 VDC to input into the Arduino to control a Red LED (when HIGH) and a Green LED (when LOW) Then have another relay make a AMBER LED (when high) fade. How do I get that 8 VDC down to 5 VDC and input it into the Arduino?? I'm using the Arduino UNO as my platform.

2

Voltage divider.

3

Hi, your description is really confusing!

  • What do you mean by "use the ground to trip a relay"?
  • How are you converting the 18-19.5VAC to 8VDC?
  • Are you using the 8VDC to power the Arduino? If so, you can probably power it with 8VDC through its barrel jack. This may mean that the Arduino will be running at a little less than 5V, but it will probably be OK.
  • Is the Arduino supposed to detect the 8VDC signal? (If so, as LarryD says, you should use a voltage divider. If you use 2 x 10K resistors, this will drop the 8V to 4V which the Arduino should read as HIGH)
  • You cannot use a relay to dim a led. They cannot switch fast enough, and would wear out very quickly if you tried.

Paul

4

PaulRB,

This should help clear up a few of your questions. I am designing this for a model RR that uses AC to drive the trains, however the signal LED's are DC. But i want to interface it to the Arduino so the Arduino can drive the LED's and give me more "Aspects" Below is a diagram how I'm going to hook up the components, however instead of the Red/Green LED im going into a Voltage Divider then into the Arduino to output back into the Signal Mast which has a tri-color (R/Y/G) LED

5

Ok, makes sense now: the 'common' rail is 0V/ground?

If so, the 10K/10K voltage divider should be fine. But for extra protection for the Arduino, you could use a Zener diode with a reverse voltage of just over 5V. This would be placed between the Arduino pin and ground and would prevent any voltage over 5V from damaging the Arduino by short-circuiting that voltage to ground. This can be very usefull in "noisy" circuits with the kind of voltage spikes caused by motors.

6

Yes the "common rail" is 0V / ground

I will look into a Zener diode.

Thanks. I should have the rest of the parts to complete this project by the end of this week. I will post the outcome when its completed.