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555 Timer Circuits

This section of EG Labs brings you some interesting electronic projects and circuits based on 555 Timer IC. These 555 timer based circuits and schematics are a good reference to learn and understand the basic timer circuits.
Latest 555 Timer Circuits

RPM counters are used to measure Speed of Motors (AC/DC) or any Rotating Object. They measures and indicates current Rotating Speed of Motor. They are very essential in applications like Speed Control of Motors and close Loop Control System. Such industrial RPM counters are very accurate made up of microcontroller or microprocessor.

The circuit presented here transmits pulses wirelessly to long distance (more than 20 meter) using keychain LASER (readily available in market). A transmitter generates continuous pulses that are fed to LASERLASER blinks at the rate of pulse frequency and emits light pulses. LDR on the receiver side, detects this light pulses and reproduces it at the output. So the same pulses that are generated at transmitter side can be received at receiver side to longer distance.

To begin with the first thing that is required for this project is to prepare LASER. So let us start with how to prepare a LASER. LASER key-chains available in the market are like this. To prepare it for the project we need to take out its anode and cathode terminals to provide pulses. In order to remove button cells and keychain part from backside of the keychain. You will see one small spring, which is cathode terminal. Connect one wire with this as shown in the figure below.

ASK means Amplitude Shift Keying (also known as ON-OFF keying). It’s one of the Modulation Scheme used to transmit Digital Data using High Frequency carrier signal. It’s very simple and popular method. It transmits 1’s and 0’s of Digital Data by transmitting carrier or no carrier like


·         Bit 1 (logic high) is Transmitted with carrier frequency Fc

·         Bit 0 (logic low) is Transmitted with no carrier


Means series of bits – bit stream is transmitted as carrier ON and carrier OFF. That’s why it is also known as ON-OFF keying.


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