How to use - USB solar charger
On a fine day, orient the cells perpendicularly to the sun using a small tool made from a piece of white cardboard and a screw (the shadow of the screw head should be projected at its base).
Hold cells in position with pegs.
Check that the red light on the USB card has lit up.
Connect the battery. The red light should normally switch off and come back after a few minutes.
Reorient the solar cells several times during the day to follow the movement of the sun.
Once the battery is sufficiently charged, disconnect it and connect a device to be recharged to its large USB socket using a compatible cable.
The box may be decorated ! 
As the power of DIY solar cells is necessarily limited, powerful devices such as the latest smartphones vsn only be recharged by only a few %.
To get more energy, you need to expose the cells for several days in a row.
It is possible to plug a USB device directly into the socket. This only works with low-power devices (e.g. small speakers, lamps, mini-fans, etc.). The cells are connected in parallel to increase the amperage while maintaining a voltage of 5 volts, corresponding to the specifications of a USB plug.
The series of cells will produce a maximum current of 5 volts and 0.75 amperes, i.e. a maximum power of 3.75 watts. With 4 cells, we could produce 5 volts and 1 ampere, which would be better.
As the current produced by the solar cells fluctuates, an electronic circuit regulates the voltage (from 0.9 V) to ensure the required 5 volts needed for a USB plug to work properly.
Inside the case of the powerbank is a 3.6-volt battery which can supply appliances with 5 volts and 1 ampere.
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