This Solar based LED flasher can Alert vehicles in heavy traffic areas or places where road work is going on. It is fully automatic and turns on in the evening. During day time it remains off and charge the battery using solar energy.
The circuit has two sections. A battery charger and a Flasher circuit. The battery charger uses 6 volt solar panel to convert light energy into electrical energy. During day time, the fully illuminated solar panel provides 6 volts DC through diode D1 to charge battery. When current flows through D1, base of the PNP Darlington transistor T1 remains positive to keep it off. So the flasher section will not get current and it remains off. When the light falling on the solar panel reduces, current flow through D1 ceases and it reverse biases. T1 then conducts as its base becomes negative. This provides current to the flasher circuit.
Flasher circuit is built around the popular binary counter IC HEF4060. A CMOS version is used to reduce the power consumption. When the IC gets battery power supply from the collector of T1, it resets through C1 and R2 and starts oscillations using R4 and C2. Out put pulses will be available from the Q3 output (pin7) causing T2 to turn on/off alternately. This makes the LED string flashing.
The circuit is designed for six LEDs using a miniature 4.8 volt rechargeable battery. If more LEDs are required, increase the value of solar panel to 12 volts and the capacity of battery to 6 volt 4.5Ah. Use High bright transparent yellow LEDs for more visibility. For portable use, fix a switch in the battery positive.