Activating a relay off an LED circuit

garymunsonJuly 21, 2013

Anyone had luck activating a small PCB relay off an LED circuit? What I would like to do is add a relay to get a make/break circuit that follows an LED. I'm assuming I'd just wire the relay in parallel with the LED but just 'upstream' from the LED's current limit resistor. Any other ideas? I do worry that whatever drives the LED won't have enough reserve capacity to power the relay coil. Wondering if I should actually cut the LED out of the circuit and use a set of relay contacts to light it from a different power source. Should an LED driver circuit be enough to run both the LED and relay coil or only one of them?

Thank you for reporting this comment. Undo

I don't yet have a relay to meter the coil resistance. I'm assuming that I'll be using a 5 volt coil one...

    Bookmark   July 21, 2013 at 10:10AM
Thank you for reporting this comment. Undo

Another thought I had was to fabricate a photo-electric circuit of some type that 'looks at' the LED and follows the operation that way with the photo circuit driving the relay. This might be outrunning my ability to design something reliable...

    Bookmark   July 21, 2013 at 10:12AM
Thank you for reporting this comment. Undo

Assuming the LED has a typical max 20ma rating, you're not going to be able to parallel a relay in there. Without knowing what's driving the LED before the current limiting resistor, it's impossible to say if it would work.

If you have access to the circuit's 5VDC to power the relay coil, maybe your could use an NPN transistor to switch the relay circuit to ground. Just run the transistor's base, through an appropriate resistor - maybe around 1K - to the LED source, collector to the negative side of the relay coil, and emitter to ground.

    Bookmark   July 22, 2013 at 10:39PM
Sign Up to comment
More Discussions
Need a new Tv, thoughts on led/plasma
Im in the market to get a new tv. I have always preferred...
Humidifier or Air Purifier?
I have been transfered to this city, with a small-size...
Best and thinnest flat screen wall mountable tv less than 20" high?
I am so out of my depth here. I would greatly appreciate...
previous post about 50ML8105D
My previous post about my Magnavox/Phillips 50"...
hdmi connection
i have a hd tv but standard cable. no hd premium service....
Sponsored Products
RGB-pixelpro-dome-50 RGB PixelPro LED Dome Module
Juno Trac-Lites 75 Watt PAR30 Flared Chrome Track Head
$25.95 | Lamps Plus
One Circuit Monorail - 4" Round Low Profile Dual Feed Canopy
LBC Lighting
Fabbian | Sospesa - D42A09
600W 12V Plug-in Remote Magnetic Transformer
Pre-lit Noble Quick Light Artificial Christmas Tree
$799.00 | FRONTGATE
© 2015 Houzz Inc. Houzz® The new way to design your home™