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”.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. 

Just as a PC software, that are being used in PCs to increase the typing skill and speed in a computer keyboard, this device has been developed to do the same job but without any PC. The device has a PS/2 keyboard port to connect a computer PS/2 keyboard (not an USB keyboard) and a LCD screen to display. When the circuit is assembled and programmed, a PS/2 keyboard has to be connected at the PS/2 socket provided in the device and it then serves as a portable TYPING ENHANCER. It needs only a 5V power supply and nothing else. It has no connection with PC. 

This device can be used to control (ON/OFF) eight high voltage electrical equipments with a remote control. The LEDs connected shows the status of the relays (ON or OFF). If one relay is ON then the corresponding LED will be ON otherwise it will be OFF. The remote control is shown in figure. The RED…

The circuit that has been designed here to extract the voice out of music channel is basically a differential amplifier build around an op amp. Two circuits are drawn, one with bipolar power supply and the other with unipolar power supply. Advantage of bipolar supply is that the output voltage swing will be greater and…

The short circuit detector described here can be used to detect short circuit condition on a LOAD operating at a maximum voltage of 12V. It is applicable to any portable devices working below 12V. The circuit employs a PNP transistor and a 555 Timer.  COMPONENTS: 1.      555 Timer 2.      PNP Transistor (2N3906) 3.      Relay PNP…

Various audio tone control circuits have been developed since the evolution of electronic audio systems. Some are being developed as passive tone control and some are active. The difference between them lies in the amplification and attenuation of the signal. An audio tone control circuit with an amplifier integrated with it is called ACTIVE tone…

  Here is the project of controlling audio volume and audio tone (bass and treble) with a remote control designed using microcontroller AT89S52.It is a mono audio controller and to make it stereo similar circuits have to be made for the both LEFT and RIGHT channels. I have not connected the components in a PCB…

  Here is the project of controlling a desktop computer with a remote control. The functions of a computer like opening and closing folders, opening media player and doing its operations, etc can be done from a distance. It requires a few hardware components to build. The project is to be interfaced with the desktop…