I am trying to make a counter which should work in a solar light. I am thinking to use two ambient light sensors placed close to each other and use a differential amplifier. One sensor receives a RED laser light and sunlight on it. The Second sensor receives just sun-light. Therefore, I would have zero volts at the output if LASER is absent or else HIGH volts if it is present. Will this work?


I have two lasers with me. (1) Red laser. 660 nm and 130mW. (2) Green laser 532nm and 50mW.

I have this sensor: http://www.everlight.com/file/ProductFile/ALS-PDIC144-6C-L378.pdf (also have 5mm too)

  • \$\begingroup\$ By the way - where possible when adding details, it's best to edit your question rather than adding details as comments - stack exchange works better that way for everyone. (Just don't change what you're asking if that makes sense). \$\endgroup\$ – CL22 Apr 8 '17 at 14:03
  • \$\begingroup\$ @Jodes Sure. I will update the question once I have more details or circuit diagram on this. \$\endgroup\$ – user5311361 Apr 8 '17 at 15:10

Yes it should work, assuming the sensors are well matched. Allow for some leeway. Eg require the signal to reach a minimum difference between the sensors before outputting HIGH. If you give more info, eg purpose of system, what's driving /controlling the laser, and that your final output is used for, I could help with a circuit.

You may be able to avoid needing two sensors if you encode the laser, or at least pulse it. For example, have it pulse at 1kHz (assuming your sensors react fast enough). Then filter out signals below that, then smooth that result and add a schmitt trigger for your final logic signal. This is the idea behind how IR remote control receivers block out ambient light from interfering. The underlying frequency, eg 1kHz is called the carrier frequency.

Either way, using a light filter which blocks everything but the laser light colour could help.

Edit: I found this circuit from here which looks near perfect:

enter image description here

As per my comment, just ignore the components after the final op-amp and feed into the MCU instead. Then just change a few values to change the reception frequency (currently 40kHz).

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  • \$\begingroup\$ Okay. How can I filter out the signals using the circuits and/or Arduino? I am just applying directly 9 volts to 5 volts buck converter and then the laser. It is rated at 4-5.5 volts. I have a thick beam red laser. I also have a green laser. \$\endgroup\$ – user5311361 Apr 7 '17 at 5:49
  • \$\begingroup\$ High pass for 1 kHz should work? I have Radioshack ambient sensors to work with. I also have photodiode and IR LED. \$\endgroup\$ – user5311361 Apr 7 '17 at 5:50
  • \$\begingroup\$ Not necessarily. Sensor reception circuitry needs to be biased such that it does not swamp with the ambient light. If it's already at the rail, no added laser light will make any difference. Modulated or not. \$\endgroup\$ – Trevor_G Apr 7 '17 at 16:55
  • \$\begingroup\$ Ambient sensors are highly unlikely to react fast enough (although I don't know about Radio Shack's). Photodiodes should work well though. Yes, a high pass at about same frequency as laser modulation, plus a bit. Perhaps 100Hz or lower might help if the photodiode or laser circuitry aren't reacting fast enough. If the laser is more than 1mW then it should easily be bright enough. \$\endgroup\$ – CL22 Apr 8 '17 at 12:11
  • \$\begingroup\$ @Trevor What kind of sensor reception circuitry do you prefer here? I have tried voltage divider and differential op-amp circuit. \$\endgroup\$ – user5311361 Apr 8 '17 at 14:58

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