Arduino powered relay behaving oddly

arduinoledrelaysparkfun

I bought a spark fun inventors kit in order to learn about arduino. I am attempting to complete circuit 13 http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Kits/SFE03-0012-SIK.Guide-300dpi-01.pdf .
It is a circuit to control 2 LEDs using a relay. I know I have the relay hooked up correctly because I can hear it click, but instead of the first LED turning off and the second LED turning on the first LED dims. Then when the relay clicks again the first LED brightens. I'm not sure what I have done wrong but no matter how many times I undo the circuit and start over I get the same result. I am especially confused because from what I understand a relay functions like a digital on/off switch. So I cannot understand why the first LED would dim instead of just turning off, even if I didn't have the second LED connected correctly.

Any tips/pointer/advice would be really appreciated. This is driving me nuts.
Thanks.

Best Answer

It seems that:

  • when the LED dims, current is flowing through the coil and then through the LED. Because the coil allow low current to flow through it, you see low brightness into your LED.
  • when the relay clicks again an high voltage is produced on the coil and the LED, then you see an high brightness in your LED. This is interesting if you are a novice because you can see your LED doing the function that, in the original circuit, would be performed by flyback diode.

Solution:

  • flip your relay left-right
Related Topic