Blinking red Led from a 2.1v solar panel

Thread Starter


Joined Mar 16, 2016
Hi All

i am very new to electronics, and am trying to build a small circuit powered by 2.1vdc solar panel (no load) to make ......

1) a Red Led blink
2) Charge a battery (AA or AAA)
3) "know" when its day or night

The general idea would be that while the sun shines it will charge the AA or AAA, and at night the little red led will flash continuously until the sun rises again, repeating the cycle day after day !

hope you can help !


Joined Jun 22, 2012
Don't think you'll do it, leds need a minimum of 1.8v to work, so thats only 0.3v less than your battery, doesn't give much headroom for current limit, you would need to use a led chip like PR4403 series.


Joined Apr 24, 2011
Charging a NiCad battery is as simple as getting a schotkey diode to put between the solar cell and the battery. But that only gets you 1.2 volts at night which is not enough to light the led.

If you open up most any garden light you will find there is a little chip in there that has the diode to charge the battery, and uses the solar cell to detect night. At night it has a simple boost converter to pump up the voltage to light a led.

The led is intended to remain on all the time. You can get LEDs that flash on their own, but that may be a problem when they are off as the booster may not see the load it needs. A Zener diode should catch that and still let the led work, but I would have to check a few things before trying that.

So I would suggest getting a little garden light and pull it apart to see what it has inside. If you see a small 4 lead device inside that is the one you want... And the thing that looks like a resistor is actually an inductor so be careful with it.