5 Questions on NE555 - Electronic Circuits Projects Diagrams Free

Suraj143 · 3rd April 2007, 06:22 AM

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.

bananasiong · 3rd April 2007, 08:45 AM

Mark time = output high = ON time

Quote:

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 %

dch222 · 3rd April 2007, 01:42 PM

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.

audioguru · 3rd April 2007, 02:23 PM

Electrolytic capacitors have a very wide range in their value. Your 10uF capacitor might be 8uF to 15uF.

Ayne · 3rd April 2007, 04:56 PM

http://www.doctronics.co.uk/programs/ic_555.exe

This will save much of ur time..

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3rd April 2007, 06:22 AM	(permalink)
Suraj143	5 Questions on NE555 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.

3rd April 2007, 01:42 PM	(permalink)
dch222	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.

3rd April 2007, 02:23 PM	(permalink)
audioguru	Electrolytic capacitors have a very wide range in their value. Your 10uF capacitor might be 8uF to 15uF. __________________ Uncle $crooge

3rd April 2007, 04:56 PM	(permalink)
Ayne	http://www.doctronics.co.uk/programs/ic_555.exe This will save much of ur time..