Light Frequency Detection

[MarcusS]

Hey all. I am looking for a light frequency sensor (possibly programmable?) that will output the frequency of light it detects in the kHz range. I am not looking for light intensity ---> frequency sensor, which seems to be common. If anyone knows of an off the shelf sensor or possibly circuit diagram for this, it would be very helpful.

Thanks,

Marcus

 

[Leftyretro]

Hey all. I am looking for a light frequency sensor (possibly programmable?) that will output the frequency of light it detects in the kHz range. I am not looking for light intensity ---> frequency sensor, which seems to be common. If anyone knows of an off the shelf sensor or possibly circuit diagram for this, it would be very helpful.

Thanks,

Marcus

Not an easy task and obtaining frequency information of light is a pretty non starter with just electronic components. I suspect your best bet would be either multi photodiode with color filters in front of them. Or some kind of color wheel in front of a single photodiode that you could sample as the various colors pass by the detector.

Good luck

Lefty

 

[MarcusS]

Well, I have successfully been able to read the frequency of a high frequency light pulse of an LED while using just a photodiode, opamp chip, and o-scope. My plan is to filter the ambient light with a band pass filter. I was just wondering if anyone has any good approaches to this with a circuit, or a pre-made chip that does all this for me, hopefully programmable.

- Marcus

 

[jpanhalt]

What pulse frequencies of light are you interested in measuring?

If you are in the 38 KHz range, you might consider hacking or copying IR detectors. Or, if you can get a LM567 (tone decoder), it may also work.

John

 

[stevez]

Years ago I built a "light listener" with my son as a science fair project. It was a photocell, 741 op amp and LM386 audio amp. You could "hear" the buzz of a fluorescent lamp, the swishing of a candle flame - and the output of a TV remote. While you can't hear 38 kHz the output of something like the TV remote did end up in the audio range because the output pulses were at least several cycles in terms of time.

I toyed with the idea of constructing a bat listener so I googled and found a number of designs. One was a heterodyne system - mixed the received frequency with a fixed frequency so that the difference was audible.

Lacking any better ideas you might combine the two projects.

As already suggested, you won't be measuring the light frequency but rather the modulation of it, so to speak. Not sure this is what you want.

 

[Leftyretro]

Years ago I built a "light listener" with my son as a science fair project. It was a photocell, 741 op amp and LM386 audio amp. You could "hear" the buzz of a fluorescent lamp, the swishing of a candle flame - and the output of a TV remote. While you can't hear 38 kHz the output of something like the TV remote did end up in the audio range because the output pulses were at least several cycles in terms of time.

I toyed with the idea of constructing a bat listener so I googled and found a number of designs. One was a heterodyne system - mixed the received frequency with a fixed frequency so that the difference was audible.

Lacking any better ideas you might combine the two projects.

As already suggested, you won't be measuring the light frequency but rather the modulation of it, so to speak. Not sure this is what you want.

"you won't be measuring the light frequency but rather the modulation of it, so to speak. Not sure this is what you want"

That is very true and why I said I don't think there is a way to electronically directly measure of frequency of light. The frequency range of visible light is 430 THz to 750 THz per the linked chart: **broken link removed**

I wouldn't be surprised if there was a way to mix an unknown light source with a fixed reference known light source and get a difference (heterodyne) frequency, but given the wide range of frequencies that cover just the visible spectrum, even that sounds pretty difficult. Anyone work in a optical lab and know more about this subject, can the frequency of light be measured directly through electronic means?

Lefty

 

[Mikebits]

I am confused. Are you trying to measure modulation or actual light frequency. A spectroscope might be good for the latter.
**broken link removed**

 

[Roff]

From his two posts, it seems clear to me that he is trying to measure modulation frequency.