Build A Digital Tachometer/RPM Counter

Current Part:

PIC 18F452 Microcontroller
PIC Programmer
IR Emitter Diode
IR Detector
5kΩ,100kΩ Trimpot
100Ω Resistor
16x2 LCD Screen
Desktop Computer Fan

Parts List Details
           Some of these parts may be new to you, others may not. Either way I'll explain what the more important parts are below to give you a better feel for what is going on and what these parts do.

PIC 18F452
           Microchip's PIC microcontroller will be used to display text to the output LCD and also for counting the pulses from the IR rpm counter circuit. The code will be shown and explained in the software section of this tutorial.

PIC Programmer
           The PICkit 2 PIC Programmer was used to put the final software code on to the pic microcontroller. I suggest using this programmer as it is both widely available and supports programming for almost all of microchip's PIC products.

           The trimpot is used as a variable resistor for both the LCD screen and for the IR rpm counter circuit. The LCD screen needs to have a certain resistance in order for the contrast to be right, then the text will show up perfectly. The digital tachometer circuit uses the trimpot to bias the IR Detector properly, sending pulses whenever there is a change between the Detector and Emitter.

IR Emitter / IR Detector
           The IR Emitter device sends an infrared signal just like any normal LED lights up a room. The difference is you won't see any light shinning from the IR Emitter because our eyes cannot see it. The IR Detector will detect if any infrared light is being shined at it. If IR light shines at the detector, it allows current to pass through it to ground.

16x2 LCD
           The 16x2 LCD gives us a nice platform for displaying text that is easily readable and very accurate. This LCD uses the HD44780 standard and is the same one that I used from the Interfacing A PIC To LCD (16×2) tutorial.