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I am looking to read the status of a battery charger using an Arduino Board. The battery charger shows red when a battery is being charged and green when a battery is charged. I understand that the charger uses a Bi-Color LED.

One option is to use an RGB color sensor (eg. https://learn.adafruit.com/adafruit-color-sensors/overview) but I am looking to see if there is any way I can read the Bi-Color LED directly on the Arduino pins.

Any ideas?

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closed as unclear what you're asking by Harry Svensson, RoyC, Dwayne Reid, Dmitry Grigoryev, Elliot Alderson Nov 13 '18 at 22:48

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ If you don't know anything about the circuit, like the led type, or how it's wired or voltages involved, the non-contact color sensor is the best way to go. Otherwise see arduino.stackexchange.com/questions/43923/… if it's DC voltage across the led and the led is a 3 pin bi-color led and not a 2 pin one. \$\endgroup\$ – Passerby Nov 10 '18 at 19:55
  • \$\begingroup\$ humptydumpty - Hi, Please edit your question and add (a) the part number and (b) a schematic if you have one, for the battery charger involved in your question. (c) It would also help to know more about the overall project e.g. is the battery being charged also the power source for the Arduino which you want to use to read the charger's status? Adding an overall wiring diagram into the question would be helpful here. || Depending on the answers to those, there can be an easy way to read the charger status. \$\endgroup\$ – SamGibson Nov 11 '18 at 0:53
  • \$\begingroup\$ Are the LED pins connected to the arduino? \$\endgroup\$ – mkeith Nov 11 '18 at 4:10
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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Opto-isolator monitoring of battery charger LEDs.

Wire the opto-isolator LEDs in series with the existing LEDs. The opto's LEDs are infrared and will drop about 1.4 V.

Enable internal pull-up resistors on the micro-controller.

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You could use a photoresistor with a red filter in front of it. The red filter will allow the LED light to pass through to the photoresistor when it is red and will block the LED light when it is green. The photoresistor will then show two different resistance readings for red verses green.

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A little known fact is that all (non-opaque) diodes (or PN-junctions for that matter) are photosensitive. LEDs in particular are the most sensitive to their own emission wavelength.

You can put together a detector by amplifying the currents in both legs of reversed-biased bi-color LEDs that are as close as possible (in distance and characteristics) to the existing ones.

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The easy way is to run a wire from the LED to the Arduino pin. At least one electrode of the LED is connected to the charge status signal. By monitoring the charge status signal you will know the LED color. The charger and Arduino would need to have a common ground.


If you wanted to go the color sensor route, you could use a photodiode like the Everlight CLS15-22C/L213(RGB).

enter image description here

See: Sharp Photodiode Application Note

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