NE555 - Let's Emit a pulse
What is 555 timer?555 timer IC could be regarded as one of the most successful chips ever made. Statistics show that 555 timer IC is the world's mostly manufactured IC with over 1billion IC's still being produced each year. From hobby electronics to engineering, 555 comes in handy in enormous range of applications. If you are a starter this is probably the best IC to start with, given its simplicity and capability.
So what can 555 do? let's get started. First application will be emitting a pulse.
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| pinout of 555 timer |
Vcc - positive supply pin
ground - ground pin
pin 2 - trigger pin. output triggers when voltage on pin falls below 1/3rd of supply voltage
pin 6 - threshold pin. 555 output goes low when voltage on the pin goes above 2/3rd of supply voltage
pin 4 - reset pin
pin 5 - control pin. As of now do not pay much attention to this pin as i will go through its uses in the next tutorials
Components needed:
R4: 100K
R1: 4.7K
R3: 470
R2: 10K linear potentiometer
C1: 47 μF electrolytic
C2: 0.1 μF ceramic
IC1: 555 timer
D1: 5mm LED
If you are unable to find some parts feel free to replace them with close substitutes. At this point what matters is seeing what is happening.
First make the connections as shown in the schematic above. Begin by turning the potentiometer(R8) to its maximum resistance. Then gradually reduce the resistance of R8. At some point you will observe LED light up, stays on for 5 seconds and go off. So that is it, you emitted the pulse, but what exactly went through? how can you customize this? let me take you through it
555 output triggered when the voltage on the pin 2 of the IC fell below 1/3 of the supply voltage(in this case below 3v). It then emits a pulse whose time length depends on R4, C1 and triggers off again. 555 in this mode is called monostable mode
So what do all the resistors, capacitors around 555 do?
R1, R2 - acts as a voltage divider to change voltage on pin2
R3 - limit the current through LED
R4, C1 - controls the duration of the pulse. If you are aware of the time constant concept you will understand duration of pulse is roughly equal to R4*C4 (time constant). Of course you will need to have a little idea of insides of 555, which is available on data sheet. And if you are unfamiliar with time constant concept just remember the result i derived
C2 - it's used to prevent any voltage fluctuations from affecting our proceedings. However it's not critical as for now
Note: You can add an electrolytic capacitor of 100uf between positive and negative supply to prevent any effect from supply voltage fluctuations
So we are done for now. You are free to customize this according to your need. Cheers :)
