Here is a trial of building a tachometer using AT89S52 Microcontroller. This is a digital tachometer which works using infrared rays. The tachometer designed here can measure rotational speed up to 4200 rpm which is sufficient for small scale use. If the speed goes beyond 4200 rpm, it gives a message on the display screen as “OUT OF RANGE”.
1. AT89S52 Microcontroller
2. 11.0592 MHz Crystal
3. 16*2 Alphanumeric Display Screen
4. 5V Power Supply
5. Speed Sensor Module
Speed sensor module:
The speed sensor module is a completely home-made module to detect speed of a rotational body. The picture of the module that I have made is shown below. The function of this module is that it converts the speed of a rotational body to pulses. These pulses are fed to a microcontroller. The microcontroller counts them and displays them with a unit of rpm.
The components required to make the module are:
1. Wheel of an optical mouse
3. Screw bearing
4. Steel rod (1 mm diameter, 10 cm long)
5. Infrared Transmitter LED
6. Infrared Receiver (TSOP1738)
7. Capacitor (47uF)
8. Resistor (100R)
Take out the wheel of a damaged optical mouse and make a hole at the center of the wheel. Put the steel rod at the hole and glue it tightly so that the rod and the wheel rotate simultaneously. Make the plywood frame as shown in figure and screw the screw bearings on both sides so that the rod with the wheel can be mounted. After mounting the rod (with the wheel) on the screw bearings, try rotating the wheel with your finger. While rotating, the rod should have a minimum friction with the screw bearings. This will help measuring the exact speed. Then make the connections of the Infrared Transmitter and the Infrared Receiver as shown in the circuit diagram. Place the Infrared Transmitter on one side of the wheel and the Infrared Receiver on another side both facing each other. Here is a top view of the arrangement.
Don’t forget to make a hole on the wheel as shown in the picture below. It is extremely important. The hole will allow passing the infrared rays from the infrared transmitter to the infrared receiver.
Now you have your speed sensor module ready. This module should have four wires coming out of it. They are:- +5V Power Supply, Power Ground, wire connecting the –ve terminal of the Infrared Transmitter and the wire connecting the output terminal of the TSOP1738 Infrared Receiver.
Let us now discuss how to connect this above made module to the microcontroller.
The circuit diagram should be connected as shown in the Circuit Diagram tab. The 5V Power and Ground of the speed sensor module should be connected to the Power supply to the circuit. The –ve terminal of the infrared transmitter and the output terminal of the infrared receiver should be connected to the specified pins of the microcontroller (see circuit diagram).