There are a number of resources scattered across the Internet that provide detailed breakdowns of common products, such as batteries, but we haven’t seen anything quite as impressive as this site. It’s an overwhelming presentation of data that addresses batteries of all types, including 18650’s (and others close in size), 26650’s, and more chargers than you can shake a LiPo at. It’s an amazing site with pictures of the product both assembled and disassembled, graphs for charge and discharge rates, comparisons for different chemistries, and even some thermal images to illustrate how the chargers deal with heat dissipation.
Mike Buss used an Arduino Duemilanove, Parallax RFID reader, micro servo, and piezo electric speaker to make a personalized, lockable keepsake box for his girlfriend’s birthday:
The outside of the box is really simple: it just contains a button and an RGB LED. When she presses the button, the LED lights up green or red depending on if the box is locked. When she waves one of the three personalized RFID cards over the box, a little tune plays and the box unlocks.
As part of the project I also did some cool trick with a Pololu pushbutton power switch to make the battery last a lot longer. Since the Arduino is only powered for a few seconds when listening for RFID tags, the battery lasts a lot longer. When the box is finished locking or unlocking (or after a small time delay), it sends a signal to the power switch to turn off the power and conserve battery life. The box has been running on the same 9V battery I put in 4 years ago!