LED signal detection in daylight

Hi,

I'm building a project robot vehicle. I need to differenciate between two LEDs blinking at two different frequencies. I need to do this in day light and from a considerable distance (about 20 meters). Any suggestions with regards to circuit design and/or devices to use? Path would be rough, therefore vehicle might have nose up or nose down while wheeling down. Appreciate all your help ! thanks

student

In day light the light is bright. You won't detect an LED at 20m. Maybe a very bright laser.

engphys said:

Hi,

I'm building a project robot vehicle. I need to differenciate between two LEDs blinking at two different frequencies. I need to do this in day light and from a considerable distance (about 20 meters). Any suggestions with regards to circuit design and/or devices to use? Path would be rough, therefore vehicle might have nose up or nose down while wheeling down. Appreciate all your help ! thanks

student

Click to expand...

I use a hood for LEDs in daylight.

My TV remote goes at least 5m in daylight.

Willbe said:

I use a hood for LEDs in daylight.

Click to expand...

A hood can't be used. It's for a race, and race rules dictate that nothing can be modified except for the car itself. Have to pick out a one of two blinking frequencies for the LEDs (at the spot, with a switch) and follow it till the end. Everything needs to be built-in in the vehicle. I was thinking photodiodes to detect the signal and band-pass filters to differentiate between the two frequencies. The LED signals can be differentiated from daylight based on their pulsing frequencies. But how can I detect the light signal from them at such a distance in daylight? Any suggestions? Any optical kind of optical filters available that will filter out the daylight? Thanks for the replies so far!

Daylight has all colours. If you filter out daylight then there is no light including the light from your LEDs. Daylight also has infrared and ultra-violet.

Maybe you can polarize the LEDs light and polarize your detector.
I used polarized sun glasses for years and they cancelled glare.

audioguru said:

Daylight has all colours. If you filter out daylight then there is no light including the light from your LEDs. Daylight also has infrared and ultra-violet.

Maybe you can polarize the LEDs light and polarize your detector.
I used polarized sun glasses for years and they cancelled glare.

Click to expand...

hmm... its a good idea. But I can only work with my vehicle. I cant alter the LED signal... thanks for the tip though.

We will be using a red LED. Would it be possible to use a filter that filters out everything except the red (in 600nm range). Even if I get day light in that wavelength through the filter.. would it be possible to somehow separate out the 1kHz drive frequency of the LED from the regular light?

Remote controls for DVD players and TVs have an optical filter so that ordinary light doesn't saturate the infrared sensor. They also have an analog filter for their 40kHz modulation.

You can partially filter light but a red filter still allows the red from daylight and nearby colours through. Then use a 1kHz filter to detect the signal.