A Tachometer is a device that measures angular $($rotary$)$ speed of a rotating object in rounds per minutes

$($RPM$).$ There are mechanical tachometers and digital tachometers, however, in this project we address

the design and implementation of a digital tachometer. Specifically, the design and implementation of a

device that counts the number of revolutions in a measured time interval and displays the value of RPM

for the given interval.

In this project, you are required to implement the system shown in Figure$-1.$ A PIC micro$-$controller should

be used to measure$/$compute the number of rotations of a rotating object in RPM every $5$ seconds. An

infra$-$red $($IR$)$ sensor module is used to detect the existence of a rotating object $$ the basic principle of

that will be explained later with the aid of Figure$-2.$

Figure$-1$: General setup.

The calculation of the RPM for a single object is done every $5$ seconds according

RPM $=$ count x $12(1)$

In case of more than one rotating object, for example a fan with N blades, the RPM is calculated by

RPM $=$ count x $12/$ N $(2)$

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where, N $=$ number of rotating objects $($e$.$g$.,$ number of blades in a fan$).$The measured$/$calculated RPM

must be displayed on a $16$ x $2$ liquid crystal display $($LCD$)$ see Figure $1.$

The system allows the user to set a threshold value for the RPM$,$ beyond which an alarm is triggered. To

make this convenient for the user, the full range is divided into four intervals $($shown in the second column

in Table$-1).$ The choice of interval is determined by selecting the correct combination of the pins of a dualin$-$line $($DIP$)$ switch $$ shown in Figure$-1.$ After choosing the interval, the user can increment$/$decrement

the count value $$ if he$/$she likes $$ to modify the value of the selected threshold by pressing one of the two

push buttons shown in Figure$-1.$ One push button for $$increment$$ and another push button for

$$decrement$.$ The micro$-$controller should do sound a beep using a buzzer and display the message $$RPM

MAX EXCEEDED!$$ as long as the measured RPM is greater than the threshold.

Table$-1$: Setting the speed threshold.

DIP switch Threshold value of count Percentage of maximum speed

$006325\%$

$0112750\%$

$1019175\%$

$11255100\%$

Detecting objects using IR

An IR sensor emit infrared light and once this light hits an object, it is reflected back to the sensor$.$

Depending on the strength of the reflected light, the sensor will know if an object exists or not and further

can know how far or close an object is$.$ The basic idea is illustrated in Figure$-2.$

In the $1990$s we used to build IR circuits and its conditional circuits from scratch in Jordan, but nowadays

we have them built as modules. For example, the HW$-201$ IR is an obstacle sensor module. The detection

range of this module is from $2$ to $30$ cm $($depending on the type and color of surface$).$ This module has a

digital output only, that is$,$ it only outputs a HIGH or LOW signal, which we can understand as logic $1$ or

logic $0.$ HIGH if an object is detected and LOW if no object is detected. This module requires $5$ volts DC to

operate.

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Figure$-2$: Basic idea of IR object detection.

Design and Development

For this project, you are required to design, implement and test the system in simulation using MPALB

and Proteus, and then build the hardware prototype for the system and test it using a rotating object.

For the software part, you need to program in assembly, and you are encouraged to maximize the use of

interrupts, subroutines and hardware timers in your design. Make sure to include detailed explanation for

your design and all the calculations that you do$.$