I'm working with this drawing to indicate the switch on a distribution panel on my boat. Green/OFF & Red/ON. 12vdc One trouble is that the total ma is quite high when you add up 8 switches. http://www.instructables.com/id/The-RedGreen-LED-Guide/step2/null/ I'm thinking it would be more efficient using transistor gates as in this 2nd drawing down on this page, but that's a single led and I want to use green/red bipolar for switch OFF/ON. Understanding Transistors Thanks for all your help.
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3\$\begingroup\$ Speaking as a boater, having an LED On to indicate that a switch or circuit is off just wastes valuable battery power. I would just use a single green LED to indicate the circuit is on, and use as high a value resistor in series with the LED as possible, while still producing adequate light from the LED. \$\endgroup\$– Peter BennettCommented Dec 30, 2015 at 3:29
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1\$\begingroup\$ Traditionally (as in military vessels) an OFF indicator avoids the situation where the circuit is ON but the indicator is faulty. More of a problem in the days of incandescent indicator bulbs, but the philosophy is not entirely without merit. \$\endgroup\$– WhatRoughBeastCommented Dec 30, 2015 at 5:26
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\$\begingroup\$ Oooarrgh boat ! As a boater I have a battery isolation switch .In some countries on some boats its needed by law .If you have a battery isolation switch the off leds would be good. \$\endgroup\$– AutisticCommented Dec 30, 2015 at 7:57
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3 Answers
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The trouble with using power (lamp or LED), well, no matter how you do it, it's still power.
Green LED is ON for when switch is OFF. Red LED is ON for when switch is ON.
No matter how you switch the LED's (switch or transistors), those darn LED's still consume the same amount of power.
Using transistors to switch the LED's on and off actually consumes a tiny bit more power.
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Yeah, I know this topic is old but so is this idea. No muss, no fuss, no power other than the LED.
It's a simple SPDT switch. Power goes in the switch common. Out one side to the load and the the RED LED, out other side to GREEN LED. LED's can share same dropping resistor since only one at a time is on. If your craft has a MASTER switch this will remove all power so there's no drain from the LED's. One warning... If you switch inductive loads the CEMF may damage the led, so use a diode ACCROSS THE led to suppress it, or, use a DPDT switch with one pole for the LED's and the other pole for the load.
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If you want to use a "bipolar LED" (I'd call them anti-parallel) like that, then you need to pick a resister that works for the voltage you have with both LEDs. Then you need an H-Bridge. Schematic example below:
simulate this circuit – Schematic created using CircuitLab
