Arduino Tachometer

Current Part:

Arduino UNO
16x2 LCD
5kΩ Trimpot
Jumper Wire
2x 2n2222 NPN Transistor
Infrared LED
10Ω Resistor
100kΩ Resistor
15kΩ or 16kΩ Resistor
Computer Fan

Parts List Details
           The parts used in this project are all listed out above, but the more interesting and necessary parts are listed out below with a little more detail to describe their function.

Arduino UNO
           This is the Arduino board that we will be using to process the IR break-beam pulses that tell us when the CPU fan has moved. The Arduino will use these pulses along with a timer to figure out what the current RPM of the fan is.

16x2 LCD
           After the Arduino has figured out what the curent RPM is, it will be displayed on this LCD so that it's obvious to the user.

5kΩ Trimpot
           This trimpot will be used for setting the contrast of the 16x2 LCD. It's gives an anaolg output varying from +5v to 0, which the LCD translates to a brightness setting.

IR Emitter Diode and Phototransistor
           The photo transistor turns on whenever intense Infrared light shines on it. So whenever the IR LED is on and shining, it keeps the phototransistor biased 'on', but if the IR LED is blocked, by...for example a CPU fan blade, the phototransistor is biased 'off'.

2n3904 and 2n3906
           These transistors will mainly be used as level shifters to ensure the pulses output from the IR break-beam to the Arduino come in the form of +0v to +5v and nothing in-between.