The goal for this project was to build it with mostly parts that I had in my lab instead of designing or buying something special so for this reason some hacking had to be done.

Thanks to the MSP430 used inside, In this video I calculate the MS6612 light meter should get up to 470 hours of continuous usage.

Solar Recharger for iPodTouch

One of the most important and available renewable energy sources is the solar power and it is believed that covering 4% of the Earth’s desert area with photovoltaic cells (cells that convert light into electric current) could provide enough electricity for the whole world. Using it may not be that easy, but solar power can be a viable option for mobile devices such as iPods, cell phones or PDAs.

This project utilizes a modified Adafruit MintyBoost Kit (a small USB charger powered by 2 AA alkaline batteries), a 3.7v 2000mAh Lithium Polymer battery, a Li-Poly battery charger and a solar cell, both from Sparkfun. The solar cell’s maximum capacity is 5v at 100mA in bright sunlight and it is used to make the whole device as compact as possible; a bigger cell could be used if faster charging is required.

The problem with the original MintyBoost is that the two AA batteries, if used to recharge an iPodTouch or an iPhone, are discharged pretty quickly so these have been replaced with the Li-Poly described earlier. The MintyBoost kit used in this project has a JST connector which connects to the Li-Poly charger circuit. The solar cell is connected to the charging circuit using a two pronged connector (you can also use another JST connector). The solar cell is then mounted on the MintyBoost metal case using 2″ wide Velcro.

You charge the whole thing by leaving it in the sun. The charger has a red LED which lights up when charging. After completion, you simply plug in your iPodTouch, iPhone or another USB-powered device you want to use. The author names this project the MightyMintyBoost since it improves the old MintyBoost with higher capacity battery and solar power capabilities. Details and pictures in the link.

Solar Recharger for iPodTouch: [Link][via]

June 30th, 2009

LiIon Battery Charger

LiIon Battery Charger

Even though not much information is published about Lithium Ion Batteries, we find them more and more often powering our portable electronics. While their price sometimes can go pretty high, LiIon batteries offer higher capacity from less weight and volume and faster charging. Laptops, portable media players, cell phones, cameras, etc. almost all use the LiIon so there is a very high probability to recover the battery from a damaged device and this way get all the advantages at a small price.

Like with other batteries, inside the LiIon type there are one to four cells connected in series, each at about 3.6-3.7V. Higher capacity is obtained by connecting series groups of cells in parallel. All is nice though until the battery gets empty, then the tricky part starts. Conventional chargers don’t work on LiIon and can even destroy them. There are some generic charges on the market but either they’re very expensive or they’re for small batteries.

Newer batteries communicate with the charger telling the settings to be used for charging. Even older batteries have a thermistor that monitors temperature and a protection against complete depletion. This being said, in this project is presented a DIY solution for a LiIon Battery Charger. There are some things you must know about the battery so that you can safely charge it.

First of all you must know the pin-out, you risk damaging the battery and/or charger if you connect it the wrong way. Then you must know the number of cells but you can determine this by dividing the battery voltage rating by 3.7V, you must also know the capacity and thermistor value. The charge current can vary between half and full capacity rating, the lower value the safest but the slower.

The charger presented in the link is based on application note AVR450 from Atmel. The project uses the AtMega8 microcontroller and it  features adjustable charging settings as well as Smart Battery Interface. Schematics and code for the Atmel are available as well as information on how to operate it. Good luck!

LiIon Battery Charger: [Link]

June 8th, 2009

Universal Battery Charger

Universal Battery Charger

When using different types of batteries it can be quite a pain in the neck to be able to find a single tool to recharge them all with, because most chargers only work with one or a few types of batteries. But here is a charger that can do it all, from sealed lead acid batteries to Lithium Ion and Lithium Polymer – the multi-chemistry battery charger.

The device has two channels and can charge two different types of batteries simultaneously up to 2 amps each. One of the channels can also be used as a discharger. The types currently supported are Nicad, NiMH, LiIon (or LiPoly), sealed lead acid and rechargeable alkaline batteries. The charger uses an ATMega32 microcontroller and a 2 x16 LCD display with a 5 key keypad that enables the user to set and view all necessary parameters, which are saved in an EEPROM and charging and discharging values. A fixed voltage, current limited output, a fixed current, voltage limited output and a variable PWM output are also provided as a bonus.

Two separate circuits are used for charging and discharging, respectively. The brain of the charger is the microcontroller working on 16MHz that generates two 10 bit 16 kHz PWM signals. It also manages the LCD and the keypad and executes the algorithms needed. Powering the microcontroller section is done using a 0.5A 5V regulator. The charger automatically detects if a battery is connected and starts charging/discharging according to the parameters entered by the user.

This project is developed as a commercial product, so no code is released by the designer. Still, he is willing to give additional information about charger design and share some of his experiences with various battery types. Also, the charger, discharger and microcontroller schematics are available in the link below.

Universal Battery Charger: [Link]

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