The circuit above implements a light switch which is activated by darkness and movement, using an LDR and a PIR sensor respectively. It draws its power from the voltage it's switching, using a 7805 voltage regulator (on the left). A manual override switch is also provided.
The sketch below implements the brains of this circuit. Highlights are:
- It smooths the light reading using an array of samples to prevent accidental triggering.
- Hysteresis also helps with this, a light reading below the light threshold is definitely daylight, while one above the dark threshold is definitely night-time.
- The light level is tunable using a potentiometer, when it's between the light and dark thresholds, an LED is lit indicating dusk.
- Another LED is lit, using the signal from the PIR, when motion is detected. This is useful when positioning the box in daylight!
- A manual override is provided to turn on the light for half an hour when it's daytime, and turn it off for 15s at night-time. (The latter allows the light to be turned off and the operator time to get out of the way.)