Amplifying an LED signal

Hi, I'm hoping someone can help me with I think should be a simple question, but it's been a long time since I did basic electronics. So I have a device on my motorbike that drives a red/green LED. Problem is I can't see the LED in sunlight so was thinking maybe I could use an optoisolator or something to switch a more powerful light source. Any suggestions? Thanks.

by Nzdude
January 04, 2017

While an optical connection is possible, it's probably simpler to connect electrically and go from there. Are there any exposed connectors you have access to? Or access directly to the LED within the device? What power buses are available? It would probably not be too hard to add an additional LED that could be controlled from the signal produced by the original LED.

by mrobbins
January 05, 2017

Good advice. The bi-colour LED plugs into a radar detector unit using 3 cores of a 4 core cable and RJ11 plug, so can access and connect to the 3 LED wires, but I don't know how much load the driving circuit will handle. Ideally I would drive a much larger and brighter LED array. To ensure their radar unit is not damaged I thought an optoislatot might be the safest option.

by Nzdude
January 05, 2017

Sorry about the delay getting the info. I have ordered a LED display and waiting for delivery.

by Nzdude
January 31, 2017
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2 Answers

Answer by mikerogerswsm

Yes, you could use two PIC817 optocouplers. Connect the inputs in place of the old leds, with a 1k resistor in series with each. The outputs will each drive up to 50mA. If you need more add a 470R pull-up resistor and a beefy emitter follower, PNP or NPN depending on polarity. The new leds will need series resistors to limit the current. Driving with undue exuberance?

+1 vote
by mikerogerswsm
January 08, 2017
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Answer by Nzdude

That makes sense, thanks. Don't suppose there's any chance of getting sketched circuit diagram please? I'm pretty rusty at this. And yes, sensible exuberance, I want to stay alive but not fall asleep!

+1 vote
by Nzdude
January 08, 2017

Yes, can do, but first you need to give us some idea of the environment. Could you sketch a circuit showing the existing items, battery (pos or neg earth and voltage) and the radar unit connector and led wiring, including polarities please. Also details of your proposed bright leds with voltage and current requirements.

by mikerogerswsm
January 08, 2017

Hi. So the main system is standard 12Vdc. The radar unit is already wired in and working, the output being the bi-colour LED connected via a RJ11 plug/socket on the radar unit. So I can cut off the existing LED to expose the three wires used, one common, one for red and one for green (I'm sure you know that). I haven't purchased the brighter LED array yet, but was thinking along the lines of this http://www.ebay.com.au/itm/232153603194 Hopefully you can follow that link, but I don't know if there will be enough information there In terms of current. Hope that helps. Thanks

by Nzdude
January 10, 2017

Okay, so the new unit is negative common, but the led current is not specified. When it arrives you need to connect it to a 12V battery with a multimeter on the 2A or 200mA range in series with one of the colours. Also is the existing radar unit output pos or neg common? Unplug the leds and connect a 1K resistor in place of one led. Use the multimeter on the 20 volt range to measure the voltage across the resistor and note the polarity. Any ten dollar hardware store multimeter will do. Interesting that modern bikes use 12V, much better than my long gone primitive nineteen fifties bike with 6V battery and magneto ignition!

by mikerogerswsm
January 11, 2017
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