The post explains a solar garden light circuit with programmable timer controller which enables the connected LEDs to light up or shut off after some delay, as preferred by the user, thus it's not entirely dependent on the solar panel parameters. The idea was requested by "Unknown".
The Circuit Request
It'd be neat if you devised a circuit that could:
1. Detect Darkness
2. Wait an adjustable amount of time, say 1-3 hours
3. energize a light, or relay
4. Stay on for an adjustable amount of time 3-8 hrs
That'd be a huge improvement over typical solar garden lights, as they typically come on too early, and stay on too long.
The Circuit Design
Referring to the proposed solar garden light with timer circuit diagram, we see a couple of IC 4060 timer stages interlinked together to form a set of sequential programmable timers.
During day time when the solar panel is active, the connected battery is allowed to charge through it, while the 4060 timers are held inactive due to the presence of the positive voltage from the panel to pin12 of the upper 4060 IC.
When darkness sets in, depending upon the selection of the zener diode between the solar panel positive and pin12 of the upper 4060 IC, the voltage is brought down to zero allowing pin12 to get a resetting zero logic via the connected 1M resistor.
Once this happens the upper IC 4060 begin counting and after a predetermined delay set by its pin9 capacitor and pin10 pot, its pin3 goes high.
The BC547 connected with this pin3 now activates all the connected LEDs illuminating them after the desired period of time has elapsed. The 1N4148 diode connected across this pin3 and pin11 of the upper 4060 freezes the IC counting process and latches the LEDs permanently ON.
However, in this situation, the lower BC547 also gets triggered and resets pin12 of the lower IC 4060 which in turn begins counting, and identically after a set period of time determined by its own pin9 capacitor and pin10 pot values switches ON its pin3.
This high from pin3 of the lower IC 4060 latches itself due to the presence of the 1N4148 diode across its pin3 and pin11, and it also grounds the base of the LED BC547 driver such that all LEDs shut off.
The entire solar garden light timer circuit now latches in this position until the next morning, when the rising positive voltage from the solar panel yet again resets the upper IC pin12 and the entire circuit. The circuit stays inactive until dark.
The cycle thus keeps repeating as explained above.
Single Adjustable Delay OFF Solar Timer Circuit
The above explained design can be simplified to obtain an adjustable delay switch OFF after the LEDs are switched ON in the evening.