After liberating the solar cell, circuit board and battery (with contacts), I saw that the main component was a YX8018 LED Controller that is used in many of the inexpensive solar powered lawn lights and decorations.  It uses the solar cell to both charge the 1.2v battery as well as determine if the LED should be turned on or off whether or not there is light shining on it.  

After taping the battery to the contacts and charging the battery, the first attempt was to just have the LED shine on the solar cell.   This had no effect, and when the solar cell was shielded from ambient light and in the dark, the LED simply stayed on.  My assumption was that the LED did not produce enough light to have solar cell generate enough voltage for the LED controller to shut off the LED.

I wanted to make the minimum number of modifications/use the least number of additional components.  By adding a 100 uF capacitor in parallel with the solar cell, I thought could fool the YX8018 LED Controller:

  • With sufficient light, the solar cell charges the battery (and the capacitor).  The LED stays off.
  • Once the solar cell is shielded from the ambient light and in the dark, the solar cell stops charging the battery and the capacitor slowly discharges.  
  • When the voltage drops low enough, the controller turns on the LED as per normal operation.  But with the little bit of light from the LED shining on the solar cell, the solar cell slowly charges the capacitor.
  • When the voltage across the capacitor rises high enough, the LED controller is fooled into thinking the solar cell is generating enough voltage to charge the battery and shuts off the LED.
  • With no light, the capacitor slowly discharges and the cycle starts over again.
  • When the light from the LED is totally blocked from the solar cell, the LED light is turned on and stays on.

By adding a single capacitor across the solar cell and shining the LED on the solar cell, when in the dark the controller turns the LED on, but the light from the LED causes the controller to turn off the LED, which makes everything dark and the cycle repeats.  Now have a blinking solar LED light!

Thought this was a nice way to abuse the LED Controller....