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I would like to make a "wake up machine" with my son. It would have a small solar panel with a small doorbell. Can I just hook up a 6V solar panel to the bell with a capacitor in between, once the cap is charged it rings the bell?

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  • \$\begingroup\$ You will need a fairly large solar panel to ring a bell, unless you include a battery. Solar charging a battery safely is a fairly complex subject. It's possible you might get somewhere with a small, efficient buzzer (maybe piezeo based?) and an ultracapacitor. Don't overlook that in many parts of the world it world for part of the year it is still quite dark at wakeup time; if you are hoping to run this from indoor lighting, that is usually far weaker than mid-day sun. \$\endgroup\$ – Chris Stratton Feb 18 '18 at 18:15
  • \$\begingroup\$ That probably won't work. The bell will discharge the capacitor faster than it is being charged. You need a circuit to detect when the voltage has reached some pre-determined level and then suddenly (rather than sunrise-style) turn on the bell. \$\endgroup\$ – Transistor Feb 18 '18 at 18:15
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You should leave the solar charging to a professional circuit, and instead have a comparator with a potentiometer and a photoresistor, so the bell turns on when there is just the right amount of sunlight. (Bear in mind the fact that you will need a large enough battery and the sun doesn't start shining at the same time every day)

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