How to Modify Arduino IR Recievers to detect Unmodulated IR?
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 &ndash; 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.