I have a simple robot which has a circuit board with motors, a flashing LED light to show the bot is on, and an LDR (plus other basic components). When normal light is shone on the LDR, the motors turn the wheels and the bot moves towards the light.
But why is it that I can shine an LED light source (such as an LED torch) onto the LDR and the bot won't move?
It works fine if I use a torch with a filament bulb or I put the bot next to a lamp.
If your LDR is a cadmium sulfide one, and If I recall correctly, the peak sensitivity is for green light, however, the usual "white" LED is a combination of a blue LED and a yellow phosphor resulting a deficiency of green. Still if the torch (flash light for us in the US) is bright enough I'd think it should work anyway.
Another possibility is that the LDR is a infrared sensitive silicon device, a visible LED produces virtually no infrared no matter how bright it is visibly. If you can get your hands on an infrared LED you might try that,
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