Rural India is slowly trying to come out of the darkness with initiatives like solar powered lamps and other such technologies. Most of the designs are simple and seem very very effective, both cost-wise and building-wise. This years IIT Bombay 2010 Techfest had some radical yet simplistic technology on display and here’s one that takes into account your health, the environment and you mobile phone is at the center of it all.

The one issue most users have with a mobile handset is battery life and in many places of rural India, electricity is sometimes scarce. Finding a suitable time and place to charge your mobile is not easy in this neck of the woods. It’s very difficult hence, for villages to keep this mode of communication alive. So as a solution, an entry at the 2010 IIT Bombay Techfest, for “Prayas-Utkarsh”, saw an initiative called the Bicycle Mobile Charger. The project was co-created by Sujay Dilip Shet, (B. Tech Electrical) and Rahul Pradip Sakharkar (B. Tech EXTC) of Dr Babasaheb Ambedkar Technological University in Lonere, Maharashtra.

Charging Your Phone on the Go
One might argue that Solar energy can be used as a viable option to charge electrical gadgets sustainability, but their maintenance and upkeep can be cumbersome and expensive. Moreover, solar panels are rendered useless during heavy rain, cloud cover and in the night time.

So why pick a bicycle to create a changing device?
The mobile charger using a bicycle dynamo is simple in design, easy to implement and light in weight. It requires minimum components and these are cheap and readily available in the market, hence making the circuit a portable one. Such a charger has a long life and comes with almost negligible maintenance costs. The entire circuit can be easily mounted in a small place or carried away if required. The cost of such charger unit may range from Rs 50 to 100, which is affordable for anyone.

The charger is not only long lasting but also does not add to the carbon footprint. The dynamo charger uses an eco-friendly way of charging the mobile. It just converts the mechanical energy into electrical energy. The charging can be done any time and in any season. The mobile can even be charged while the user is on his way to work.

Understanding The Design
The device is made of a dynamo charger which is uncomplicated. The charger has a simple design and consists of a bridge rectifier with four diodes (1N4001GP). The frequency of input voltage required to charge the mobile is minimum 45 Hz and the input resistance of IC LM7806 is assumed to be 500 ohm. The expression for ripple factor using pi filter is given bellow:
r = ________________________
4*√2 * ω * ω * C1* C2* L*RL
Where, ω =2*pi*f
f =input frequency
C1, C2 =Capacitors used
L =inductor
RL =Load resistance= Input resistance of IC
To get 5% ripple we have from above formula
C1*C2*L=88.45 nano
If C1=C2=C=1000 micro farad
L=18 mH
Let us select 10 mH inductor.

Typical output current of IC LM7806 is 1 A, so to get 350 mA of current, for successful charging of mobile a 100 ohm resistor is placed across the input resistance of mobile which is approximately 180 ohm. The connection diagram is shown in Fig (1) and output in Fig (2) on the following page. As for the circuit configuration, the variable output up to 12V AC from the dynamo when cycle is in motion is given to bridge rectifier that converts AC input voltage into pulsating DC output voltage.

The AC voltage is filtered out from this output voltage through pi filter. This gives around 99% pure DC output voltage. This is not suitable to charge the mobile because as input AC voltage from the dynamo varies the output also varies. Stabilized voltage of 6 volts DC is obtained through a positive regulator IC LM7806. The output current of IC is typically 1A. Current divider circuit gives 350mA of current for successful charging of the mobile.

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