This simple project can be used to generate sound which can be heard through a speaker or a buzzer by connecting either of them to its output. The idea is to generate a frequency in the audible range from a normal pulse generator. Using the circuit in a battery saving mode so that it can work for a longer duration is made possible by using a 555 IC. This IC is known to work in three different modes: bistable, astable and monostable, and can work efficiently in all three modes. Also, being casted in an integrated circuit format makes 555 a power efficient and it can be stretched to work for a longer duration.
NE555 is a highly stable controller capable of producing accurate timing pulses. In this project, NE555 is operated in astable mode, i.e., to generate pulses of pre-calculated frequency. In astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multivibrator. With this operation, the frequency and duty cycle are accurately controlled with two external resistors and one capacitor. The frequency of the output pulse is given by the relation:
f = 1/T = 1.4/(R1+2R2)C2
By adjusting the values of the capacitor C1 and resistors R1 & R2, the output frequency of the NE555 can be brought in the audible range of 20 Hz to 20 kHz). Typical values that can be used in this circuit are, C1= 0.1uF, R1= 2k (variable), and R2 = 10 k (variable).
This output of the circuit is filtered by a capacitor and can be supplied to a speaker or a buzzer which will produce sound the sound of calculated frequency.
Filed Under: 555 Timers, Electronic Projects