How Can a Sensor Detect Green LED States?

In summary, the conversation discusses the need for a sensor to monitor a standard green LED and determine its status. The options of using a phototransistor or photodiode are mentioned, with suggestions for the specific wavelength and sensitivity to consider. The challenge of detecting the LED's blinking rate is also addressed, with a logic probe circuit recommended as a possible solution. Ambient lighting and proximity to the LED are also important factors to consider.
  • #1
dsimp
2
0
I'm doing a project where I need a sensor to monitor a standard green LED and determine if it is ON, OFF, or BLINKING. I have been considering using a phototransistor or photodiode, but I am not sure how I would use one of these to tell the difference in the LED being on or blinking.

Does anyone have any experience with something similar to this?
 
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  • #2
What is the environment of the application (distance from the sensor, ambient lighting, sensor output requirements, etc.)

A good place to start if it needs to be optical is to determine the wavelength the sensor is required to detect (green in this case) - 500-~580nm.

this is especially important if ambient lighting is a factor - you want the sensor to be mostly sensitive to the light that you are trying to detect.

With a photo transistor, you should be able to read this just like a normal transistor which makes the rest pretty straightforward.

The photodiode approach will give an analog voltage (you can use a comparator to get digital if needed). With the circuitry you set-up for the photodiode, the blink rate of the LED can become your largest challenge. If you use a large capacitor, it might not discharge in time to detect the flashing.
 
  • #3
That sounds like a logic probe.

Have a look at this circuit:
http://ecelab.com/circuit-logic-probe.htm
http://ecelab.com/circuit-logic-probe.jpg
This would go after your photo-transistor detecting circuit.

or search Google for logic probe circuits.
 
Last edited by a moderator:
  • #4
Thanks for the responses. I will look into those solutions. The detection would only need to occur from a short distance (within 10cm). The lighting is a little bit of a wild card, but it will be used indoors with variable lighting.
 
  • #5
If you can connect to the LED directly, the approach as recommended by vk6kro is ideal.
 
  • #6
Your detector would probably have to be very close to the LED and ideally mounted so that ambient light could not reach the detector.

Otherwise, it is going to be very difficult to tell if light is coming from the LED or from room lighting.

As MDJensen says, if you can access the wires going to the LED, that would be a lot better. You need several volts to drive a circuit like the logic probe above and it is going to be difficult to get that much signal from a light detector.
 
  • #7
If ambient lighting is a concern, you could always use the Photodiode and baseline out the ambient level and look for a change in the reading - maybe you end up using two sensors - one to look at the led, and one to read the ambient lighting.
 

Related to How Can a Sensor Detect Green LED States?

1. How do LEDs work?

LEDs, or light-emitting diodes, work by converting electrical energy into light energy. When an electric current passes through the LED, it causes electrons to move within the semiconductor material, releasing energy in the form of photons (light).

2. How can you tell if an LED is on or off?

The easiest way to tell if an LED is on or off is to look at its color. When an LED is on, it emits a specific color of light (such as red, green, or blue). If the LED is off, it will not emit any light and will appear black.

3. How can you detect different LED states?

To detect different LED states, you can use a multimeter or a specialized LED tester. These tools measure the voltage and current passing through the LED, allowing you to determine if the LED is on, off, or malfunctioning.

4. What are the common causes of LED failure?

There are several common causes of LED failure, including overheating, power surges, and manufacturing defects. LEDs can also fail due to age and wear, as they have a limited lifespan.

5. How can you troubleshoot LED issues?

To troubleshoot LED issues, you can start by checking the power source and connections to make sure they are secure. If the LED is still not working, you can use a multimeter to test the voltage and current. If all else fails, the LED may need to be replaced.

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