Latch-up circuit using 555 and opto-coupler

Here’s a simple latch-up circuit using 555 timer and opto-coupler MCT2E. You can also use PC817 in place of MCT2E.  The NE555 timer is configured in astable mode.The components are selected in such a way that the frequency output of the astable circuit lies within the audio range. Opto-coupler, MCT2E is is used for latching the alarm.Under normal conditions, pin 4 of NE555 timer is set to ground via resistor R2(470Ohm) and its output at Pin 3 is held LOW. When switch S1 is pressed momentarily, transistor T1 (BC548) conducts to bring reset pin 4 to logic “HIGH” state, as a result, 555 timer activates and starts the sound and the LED inside the optocoupler glows and the phototransistor conducts. The transistor gets base bias via phototransistor and resistor R6(470R). The sound remains ON till you press the reset switch(S2).  When switch S2 is pressed, the base of the transistor connects to the ground(0V) and resets the 555 timer bringing Pin 4 to LOW state. This disables the alarm. (more…)

MINIBREAD

MINIBREAD is a simple technique of making electronic projects on mini breadboard. I have published basic electronic projects keeping electronic amateurs and students in mind. (more…)

Astable mode of 555 timer

Description: Astable mode of 555 timer is used to generate pulses at regular interval. READ ABOUT ASTABLE MODE. 

The following schematic has been taken from buildcircuit.com. The following circuit can work as a music generator, Infrared transmitter and LED blinker depending upon the values of R1, R2 and C1. (more…)

Monostable module

Description: In the monostable mode, the 555 works as a “one-shot” pulse generator.  Other applications of monostable mode include timers, pulse-width modulation (PWM), missing pulse detection,  touch switches, frequency divider, capacitance measurement, bouncefree switches  and so on.  (more…)

FREE 555 timer simulators for electronics beginners

All of us know that NE555(or other versions) is a versatile IC for building big and small projects. Recently, I found some free simulators that would be very useful for electronics beginners. Please go the links I have given on this page and download those applications for FREE. You may also find something more useful on those pages. I will update this page again once I find more simulators. Please write me if you know any. (more…)

Light activated police siren using 555 timer and light dependent resistor(LDR)

Here’s a simple light activated police siren using light dependent resistor and NE555 timer. Before you make this project, I would recommend you to make the following projects.

a. Light sensor and dark sensor

I strongly recommend you to make a dark sensor and light sensor using LDR and understand clearly how it works.

b. NE555 astable mode– Understand the working of astable mode of NE555 timer.

The police siren project is based on these two projects, so you need to understand these two projects first. (more…)

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