Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

5 Questions on NE555

Status
Not open for further replies.

Suraj143

Active Member
I’m using NE555 in ASTABLE mode. I want to turn an LED on & off continuously with these requirements.

ON time 3 Seconds
OFF time 1 Second
(LED will turn ON 3S & OFF in 1S)

These are the formulas I used to calculate my R1 & R2. C1 I used 10uF.

Mark time (output high): Tm = 0.7 × (R1 + R2) × C1

Space time (output low): Ts = 0.7 × R2 × C1

After calculating I got this values.
R1=285 Kohms
R2=142 Kohms

Questions

1) Is my values correct?

The duty cycle is the proportion of the complete cycle for which the output is high (the mark time).
The duty cycle formula is given by D = Tm / (Tm+Ts).

2) What is the different between Duty cycle and the Mark time? These both are depending on ON time?

3) What is the meaning of 90% duty cycle? Is that the mark time is ON for 90% & the other 10% is space time?

4) In my earlier example the duty cycle is 0.75.Is that means the mark time is 0.75? But I calculate the Mark time as 3 seconds.

5) If I want to turn ON an LED bulb for a calculated time and OFF for another time do I need to consider about Duty Cycle? Or can I ignore that.
 
Mark time = output high = ON time

4) In my earlier example the duty cycle is 0.75.Is that means the mark time is 0.75? But I calculate the Mark time as 3 seconds.
ur duty cycle is 75 % Because the full cycle is 4 second, 3 second on time, 3/4 x 100 % = 75 %
 
The values you have calculated look OK, but you may get some inaccuracy because of the leakage through the electrolytic cap which makes it discharge slightly faster than you expect.
 
Electrolytic capacitors have a very wide range in their value. Your 10uF capacitor might be 8uF to 15uF.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top