HillHacks Lantern

One of the most important part of HillHacks is its school program where hillhackers conduct workshops free of cost for the local school kids. Previous edition school programmes have included(source hillhacks):

  • Makey-makey electronics
  • Paper circuits
  • Electromagnets
  • Mapmaking
  • Programming Arduino
  • Cryptography
  • Theatre
  • Circus arts
  • Rubik’s cubes
  • Solar lanterns
  • Audiobook recording
  • Electronic music

This year at HillHacks 3 I also wanted to teach kids how to solder. I believe that’s an essential skill every kid should have along with programming. During the HillHacks 0 that happened in the year 2014 my friend Akiba brought some solar lanterns based on cl0116 IC from Chiplink. That’s a pretty cool IC which drives the LEDs and takes care of charging a single NiMh battery via a solar panel. Both functionalities in a single TO-94 packaged silicon die. Since I didn’t have much time to think of a design from scratch I decided to modify Akiba’s design and added an astable multivibrator to add a blink feature to the LEDs and make it more fun for kids. Also, instead of using cl0116 I used qf5252 which is almost similar except that it has a different pinout and a cutoff voltage of 0.8v instead of 0.6v with cl0116.

The lantern has got two modes: blink and hold. In the blink mode the LEDs blink alternatively in an astable multivibrator mode with a time constant set by R1,C2 and R2,C3. While in the hold mode both LEDs will glow simultaneously. Components used:

  • qf5252 as solar charge controller and booster.
  • L1 inductor = 100 uH. We can use anyvalue between 100-330 uH. Lesser the value brighter will be the LEDs.
  • C1 = 10uF filtering cap.
  • C2, C3 = 47uF. Decrease this to blink the LEDs faster.
  • R1, R2 = 150 Kohm. Alternatively, these values can also be reduced to blink LEDs faster.
  • R3, R4 = 220 ohms.
  • Q1, Q2 = PNP 2N3906 transistor.
  • D1 = 1n5819 schottky diode.
  • D2, D3 = 1W LEDs. Warm white looks great.
  • Solar panel = 2V 130ma(260mW). Any 2V panel can be used. More the wattage, Faster would be the charging.

Schematics and project files can be found on the project’s github page. Here are some videos of the lanterns.

“Blink” mode:

“Hold” mode:

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