This is a small, off-the-shelf, DIY digital tachometer that uses a photo-interruptor (IR emitter/detector) to keep track of the RPM of anything. It's a simple yet very effective design that I thought you guys might like. The RPMs of a desktop computer fan are tracked as an example with this system Follow the Link http://www.pyroelectro.com/tutorials/digital_tachometer_rpm/ Submitted by : Ch... more.

Here is a solar charger circuit to charge Lead Acid or Ni-Cd batteries using solar energy. The circuit harvests solar energy to charge a 6 volt 4.5 Ah rechargeable battery for various applications. The charger has Voltage and Current regulation and Over voltage cut off facilities. The circuit uses a 12 volt solar panel and a variable voltage regulator IC LM 317. The solar panel consists of sola... more.