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Return to BlogMailbox Project Powered by Solar Energy
Posted Feb 07, 2012 at 11:50 am
Figure 1
The project aims to use the sun to provide power to a self-sufficient mailbox wherein the number of the house is displayed depending on the level of the battery.
A 5V 80mA Polysilicon solar cell is used to provide power on the Mailbox while the three AA NiMH batteries are charged with the sun energy. When there is not enough light to charge the battery, the system must work autonomously. The 3 digit is being driven by the PIC according to a sequence that is defined in its program when there is no light especially during night time. The PIC is running with infinite loop where the period is approximately 1 second as the red LED blinks accordingly when the battery is totally low.
Through the Sziklai pair composed by 2N2907 and 1N1711, the 3 AA NiMH cell are charged by the solar cell. When the sun is off and the battery is at full charge, this is necessary to ensure a very low reverse current. In order to prevent the battery for overcharging which will degrade significantly its lifetime, the value of Zener diode should be 4.6V for battery protection purpose.
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