On, off LED circuit

Thread Starter

heywood

Joined Dec 17, 2008
2
Hi, I'm trying to do something pretty basic, power a Green and a Red LED based on the state of a switch, on/closed or off/open. When the switch is closed, I'm also powering a relay coil. This is what I have come up with. I'm curious if there is an easier way to do this or with fewer components.

 

eblc1388

Joined Nov 28, 2008
1,542
I would say one has a 99.9% chance of success if the circuit is for low voltage(12V or less) relays. Most of them have coil resistance less than a few hundred ohms.

Furthermore, one could also use high intensity LEDs that take 1mA or less so the circuit will most definitely works.

However, I do agree it is a different story for special or high voltage relays that has high coil resistance.
 

Thread Starter

heywood

Joined Dec 17, 2008
2
Thank you very much for the suggestions. The input to open and close the switch is actually a ground signal (floating=open) coming from an ECU so unfortunately I can't do too many clever things with switch.

I do think that the right side transistor can be deleted. I don't see why I can't power the relay + green LED directly from the signal line.

I need to study more the suggestion to chain the LEDs together. At first glance it would seem that the relay would always be powered but I guess I need to look at the math more closely. It's certainly a very simple solution.
 
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