So, after distributing kits to kids at hillhacks last year few complained that fully charged lantern is getting discharged even when the lantern was switched off via switch U1 in the previous schematics. After a closed inspection I realised that q5252 ic has some leakage current which discharges the battery within one day. To fix this I have added an another switch SW1 next to the battery (just for this version though, see below schematics). So now people can store a charged lantern in dark by switching off this switch and there won't be a leakage of current.
Caveat is that to switch on the lantern again we will have to switch on two switches now, i.e. both SW1 and U1. This is not the best design whch I will try to fix in the next version.
First circuit boards arrived. I also made few custom circit boards for Hill Hacks with Hill Hacks logo on them. These boards are meant for Hill Hacks conference and its school program. The components are meant to be soldered on the front side of the board. While the back side is just for marketing purpose :)
The entire circuit runs on a 1.2V NiMh battery which gets charged by a 2V solar panel. The board has got a qf5252 ic. This is a tiny but very interesting ic which serves as a switching boost converter and solar charge controller. It only need and external inductor for boosting a 1.2 volt NiMh battery sufficiently high to light LEDs. It runs at a frequency of around 100 Khz.
I filtered the spikes from the boost converter and added an astable multivibrator to blink two leds alternatively to make it more fun for kids. This blinking mode can be disabled with a switch so that the lantern will glow continuously.
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.
Here are some photos from the event:
At Knowledge Garden, Upper Bagsu Dharmashala, India.
Knowledge gargen in upper Bagsu is a smaller hacker space promoting DIY repair culture among the people in mountains. Here are some pics of Pranshu and Shubham learning how to solder. :)
At Tibetan Children’s Village (TCV) school in Suja, Bir, Himachal Pradesh, India
As a part of HillHacks school program we conducted a soldering workshop at TCV Suja. The school is located at the foot steps of Dhauladhar mountains of Himalayas. The view from the school is breath taking. I wish I had a school like this. Around 30 students from 6th grade participated in the workshop. To my surprise some kids soldered better than few adults at Hillhacks :), probably because they had more hands as can be seen in the below photo.
Nitesh Kadyan
Kids who participated:
