I'm trying to find the easiest way to interface between an Arduino IR receiver and an IR flashlight.
Yesterday I learned a lot from a question: Can Arduino IR Recievers Detect Signals from IR Flashlights? Basically, the moral of the story from that was, at least with that particular Arduino IR receiver, it expects a modulated frequency in the IR signal. That means that remotes can work well with such receivers. On the other hand the IR flashlight would not, because it is not modulated.
Since then, I have been thinking about the best next step to tackle the problem. I now turn my interest to modifying the Arduino module. Not only do I believe reworking the IR flashlight may be more difficult in comparison, but also I need to keep the IR flashlight's signal intact.
Question: Is there any hope for modifying an Arduino IR receiver module to capture unmodulated IR? Or perhaps even better, is there an off-the-shelf solution that could work for me?
Further Clarification
- Signal: I need to work with an unmodulated signal, the IR flashlight's IR must remain on and uninterrupted. it has beam mode and flood mode, ideally the solution would be robust to both
- Range: I would like it to be sensitive to at least 10 yds, ideally much further
- Environment: I have a night-time environment in mind, so the ambient IR should be minimal, hopefully only the IR flashlight will be detected
- Application: For the moment, this is nothing too fancy, I would just like to have a green LED to light up if the module is hit by my flashlight's IR
- Duplicate Distinction: allow me to explain my rationale. The prior post I asked about the proof of concept. In this post the focus of the question was on implementation and hardware/software selection and modification. While the subject matter of the two posts are identical, the scope of the inquiry is different. After I got the community's feedback about the first question, I was able to contemplate and think on how to approach the problem with a better understanding of the underlying principles. At least in my mind, each post served a distinct purpose. Perhaps if I had combined them into one question it would be more concise, but given all the new material (to me) that has unfolded in this discussion, I probably would have butchered the terminology/physics to even phrase a question that wasn't really confusing. I decided to err on the side of safety and take it step by step and only ask a specific question once I was confident that I knew how to formulate that question in a clear and scientific way.
Best Answer
You cannot modify an existing receiver, because the demodulator is in the same package as the sensor device. They cannot be separated without destroying them.
Instead, you need a bare phototransistor, which is like a regular bipolar transistor but conducts when light strikes it instead of having a base terminal. Choose one which has a built-in infrared filter if you can, so that it does not respond to other light as much. (A photodiode can also be used, but it responds faster with a weaker output — it is good for modulated IR but not what you need.)
simulate this circuit – Schematic created using CircuitLab
(CircuitLab doesn't have a phototransistor symbol, so I used a regular transistor. The proper symbol is just this but with the "incoming light" arrows added.) The resistor should be large enough to limit the maximum current when the phototransistor conducts (no less than 100 Ω but possibly much higher), and otherwise chosen by experiment to produce a reasonable range of values depending on the illumination.
You will likely want to use one of the analog input pins on your Arduino so that you can choose a suitable activation threshold in software. Without modulation to help, choosing a useful threshold is hard, because ambient light — especially sunlight — includes infrared. You may want to write code to detect, not a certain absolute level, but a relatively sudden increase (as when the flashlight is turned on or moved to strike the sensor) — a high-pass filter.