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.

 

1-10 Minute Adjustable Timer using 555 IC

This project uses 555 timer  IC in monostable mode. The circuit starts timing when switched on. The green LED lights to show that timing is in progress. When the time period is over the green LED turns off, the red LED turns on and the bleeper sounds.

The time period is set by adjusting the variable resistor. It can be adjusted from 1 to 10 minutes (approximately) with the parts shown in the diagram. You can mark the times on a scale drawn on the box.

 Source: http://www.kpsec.freeuk.com/projects/timer.htm

Online Resources for 555 Timer IC

The 555 timer IC was first introduced by the Signetics Corp. in 1971. It has been more 35 years and this IC is still very popular among hobbyists and is used in numerous projects. With just a few external resistors and capacitors, it can be used to build many circuits and you don't even need to understand the function of each pin in detail. It has 8-pins and it is frequently used in astable mode to generate a continuous series of pulses, and in monostable mode too when one shot or pulse of desired time period is required.

The internal block diagram of a 555 Timer IC is shown below.

Source: http://www.ibiblio.org/kuphaldt/electricCircuits/Exper/45005.png