555 Timer for 1 Hz with 0.1 % duty cycle.

[amayilsamy]

How to make 555 Astable multivibrater for 1 Hz?

Duty Cycle On Time=0.1 ms, Off time=999.9 ms.


Or Which is the best way for 0.1 % duty cycle in 1 Hz.


Thanks in advance.....

 

[crutschow]

One good way is to use two 555 (or one dual 556) timers. The first is an astable with a 1s period. This triggers the second 555 which is connected as a one-shot (monostable) with a 0.1ms period.

 

[BradtheRad]

Each pulse is .001 second long, at a time period of 1 Hz.

Just to see if it is possible, I tried it with a single 555. With careful adjustment I managed to get pulses .002 sec long.



The scope traces show that the capacitor charges and discharges inside a range of 26 mV. That is how small the adjustment gets, in order to obtain the narrow duty cycle.

Furthermore a change in duty cycle causes a change in overall time period, and vice versa.

Crutschow's recommendation of two 555's will be easier to get right. The time periods can be adjusted independently of the other.

 

[amayilsamy]

Thanks for Both of you.

How it possible in dual timers. Help me out how to do it. I need exactly 0.1 ms on time in 1 Hz....

 

[godfreyl]

You could use standard astable circuit below with:
R1 = 2.2 Megohms
R2 = 220 Ohms
C = 0.68uF

That should oscillate at about 1Hz, with time high = 1S and time low = 0.1mS.

To get the waveform you want, just invert the output from the 555. You can use another 555 as an inverter.

 

[crutschow]

Thanks for Both of you.

How it possible in dual timers. Help me out how to do it. I need exactly 0.1 ms on time in 1 Hz....

How exact is "exactly"?

 

[amayilsamy]

I already do it with single timer. Can't achieve 0.1 % in 1 Hz. Its 0.4% in 1.025 Hz. So, I need near than 0.1 % in 1 Hz with maximum 2% errors.

 

[crutschow]

I already do it with single timer. Can't achieve 0.1 % in 1 Hz. Its 0.4% in 1.025 Hz. So, I need near than 0.1 % in 1 Hz with maximum 2% errors.

For that accuracy you will either have to go to a crystal controlled oscillator and counter or use trimpots to tweak the resistor values for the 555 to get the desired frequency and period.

 

[neddie]

Do it with a 8-pin micro. Then sand off the top of the micro and write 555 on top :0)