Understanding IC 555. Design note 3

We all used IC 555 in many applications. Why it is called as 555 Timer? There are three 5K resistors inside the IC that makes it as versatile IC for Timer applications. IC555 was introduced in 1971by the Signetics corporation as SE555 / NE555 and was called as IC555“IC Time Machine”. Later its CMOS version IC 7555 and Dual Timer IC 556 were introduced.
Continue reading “Understanding IC 555. Design note 3”


Flip-Flop control using LDR. Sensor Circuit 10

IC 555 has an internal Flip-Flop and its working determines the output state of the IC. The discharge input of the IC has an NPN transistor with open collector. The On/Off of this transistor also depends on the state of the Flip-Flop. The Flip-Flop is under the control of the lower and upper comparator of the IC which can be independently controlled by external voltage. Here two LDRs are used for controlling the comparators.

Continue reading “Flip-Flop control using LDR. Sensor Circuit 10”

Movement Detector. Sensor Circuit.4

Here is an LDR based movement detector for day time use. It is highly useful in shops, banks etc to confirm the entry and exit of persons. It uses two LDRs and the popular timer IC555.

Continue reading “Movement Detector. Sensor Circuit.4”

Thermister based Fire Alarm. Unusual Design 4

What happens when only a few pins of 555 is used? Still we can make circuits. Here ,is a simple Fire alarm  based on IC555. The trigger pin2 is used to achieve the result in addition the VCC and Ground pins. In this design, the IC555 act like a switch to give  high output. When the temperature in the Room or a device exceeds the set limit, alarm sounds.
Continue reading “Thermister based Fire Alarm. Unusual Design 4”

Unusual 555 Oscillator. Unusual Design. 3

IC555 is making me happy. This tiny chip can be exploited in many ways. Here I am using Output pin3 and Threshold pin 6 to make an Audio oscillator. Another unusual way to design an Astable.
Continue reading “Unusual 555 Oscillator. Unusual Design. 3”

555 Sound Transmitter. Unusual Design 2

Not satisfied with IC 555 design. Now I am going to exploit its Control voltage pin 5. This pin is used to give a controlled voltage to control the working of the Flip-Flop inside the IC. But if it is not used, it will be connected to the ground through a 0.01 disc capacitor. I am going to give a minute voltage into this pin. Let us see what happens.

Continue reading “555 Sound Transmitter. Unusual Design 2”

Timer with a difference. Unusual Design 1

You know the working of 555 Timer and a number of circuits using the IC 555 are available. But I am experimenting with this unusual design. It will give more time delay than the usual 555 Monostable design which gives only maximum 3 minutes. See the trick.

Continue reading “Timer with a difference. Unusual Design 1”