It is also possible to construct an active reflector to alert the drivers of a pedestrian crossing the road. Presented here is the circuit of an active reflector that can warn the drivers even when no light falls on it. Even without the ambient light or vehicle headlight falling on its sensor, the LED blinks.
The circuit (Fig. 1) consists of a light-dependent resistor (LDR1), timer IC NE555 (IC1), transistor BC547 (T1) that acts as a buffer and LED driver, and a bright red LED (LED1). NE555 timer is configured in oscillator mode. When ambient light is dim, there is a potential drop across the light-dependent resistor below the level set by the combination of VR1 and R1, and reset terminal (pin 4) of NE555 goes high to enable the oscillator.
Transistor BC547 (T1) then switches LED1 on and off at the oscillation frequency. Resistor R3 (220-ohm) limits the current through the LED to a safe value. Sensitivity of light sensor LDR1 can be set using potentiometer VR1.
After construction and testing, house the circuit in an appropriate cabinet with LDR1, VR1 and LED1 mounted on the front panel. Mount LDR1 such that LED light does not fall on it. Glue a piece of self-adhesive black sheet marked with a transparent pedestrian symbol to the front panel (refer Fig. 2). Next, attach a cloth peg at the rear side of the enclosure using a suitable screw and attach the reflector to the cloth with the cloth peg clip.