Sunday, January 23, 2011

Overload protection circuit using 555 timer

-Vijay Kumar P.
Overload protection circuits are required in inverters and uninterrupted power supplies to make sure that the loads connected to them do not exceed the maximum power ratings. This project describes a simple overload protection circuit based on a 555 timer IC. The current drawn by a load is sensed through a 5 W 1 Ohm resistor. The voltage drop across this resistor is proportional to the current drawn and hence can be used to sense any short circuit of excess load current. An optocoupler is used to isolate the mains AC part from the rest of the circuit.

Smoke alarm project using 555 timer IC

-Pradeep G
This project uses a 555 timer IC with an optical sensor to create a smoke detection alarm system. The optical sensor consists of an IR diode and a photodiode with a small gap in between. During normal condition the photodiode is receiving the IR signal from the IR diode. The presence of smoke interrupts the signal to the photodiode which in turn activates the 555 timer IC to generate alarm. The timer IC is configured as an astable multivibrator with a frequency in the audible range.

Audio amplifier for condenser mic

- D. Prabakaran
This is a low cost condenser mic amplifier that provides amplified audio output of 0.5 watts at 4.5 V supply. The preamplifier portion uses two BC148 transistors that amplifies the weak audio signal output from the condenser mic. The output of the preamplifier is fed to the input of a BEL1895 IC. It is a monolithic audio power amplifier commonly used in AM radios. The output from the power amplifier drives a 4 Ohm speaker through a coupling capacitor C14 (470 uF).