Need a 50% duty cycle corrector

[ariakovo]

Hi all,

I have a clock (ne555) that has 20% duty dycle and I want to change duty cycle to 50%.I don't want to change the frequency just the duty cycle.The phase mus't change a lot.I can't play with the ne555 because I transmit this frequency and then I want to have this frequency in the receiver but I want it in 50% duty cycle.Also I can't make the same (or a similar) circuit in the receiver because I want to synchronize the two components (frequency drift etc).So the only way is to transmit the frequency.

Thanks for your time

 

[Roff]

Will the frequency be changing? If so, at what rate?

 

[ericgibbs]

Hi all,

I have a clock (ne555) that has 20% duty dycle and I want to change duty cycle to 50%.I don't want to change the frequency just the duty cycle.The phase mus't change a lot.I can't play with the ne555 because I transmit this frequency and then I want to have this frequency in the receiver but I want it in 50% duty cycle.Also I can't make the same (or a similar) circuit in the receiver because I want to synchronize the two components (frequency drift etc).So the only way is to transmit the frequency.

Thanks for your time

hi,
A simple way for a precise 50% duty cycle is to double the frequency of the 555 and drive a divide by 2 bistable.

It is possible to get a 50% duty cycle for a 555 by using variable resistors for both the R/C timing and/or by pass diodes.

I would recommend the first option, because as you vary the 555 freq the duty cycle is always 50%.

 

[audioguru]

With two diodes and a pot then you can adjust the duty-cycle of a 555 to anything you want.

 

[ericgibbs]

With two diodes and a pot then you can adjust the duty-cycle of a 555 to anything you want.

I 'think' he is saying he wants to vary the basic freq of the 555, if I am reading his post correctly.????

 

[audioguru]

He wants a fixed frequency but wants a 50% duty-cycle.

Then maybe a CD4047 IC should be used. It has an oscillator with one resistor and oune capacitor. It has a digital divide-by-two to give a perfect 50% duty cycle. It has two outputs with one inverted if it is needed.

 

[ericgibbs]

He wants a fixed frequency but wants a 50% duty-cycle.

Then maybe a CD4047 IC should be used. It has an oscillator with one resistor and oune capacitor. It has a digital divide-by-two to give a perfect 50% duty cycle. It has two outputs with one inverter if it is needed.

If he ever comes back he will hopefully give us more information.

It would nice to know, what exactly he is trying to do with system as a whole.

 

[ariakovo]

hi,
A simple way for a precise 50% duty cycle is to double the frequency of the 555 and drive a divide by 2 bistable.

It is possible to get a 50% duty cycle for a 555 by using variable resistors for both the R/C timing and/or by pass diodes.

I would recommend the first option, because as you vary the 555 freq the duty cycle is always 50%.

Sorry for not answering I had a problem but I am back.
I know how to make a 50% duty cycle squeare signla (with a crystal for example) but i want to transmit this frequency in 20% duty cycle and the i want to take this frequency in the receiver and change it to 50% duty cycle but i want the frequency remains the same and of cource not a big chane in the phase.The frequency doen't change (150Hrez).Imagine that someone gives you a frequency in a wire and he tells you that i have a 150Hz frequency in 20% duty cycle and i want an electronic component that in the input it takes the frequency i give you and in the output i take the same frequency but in 50% duty cyle and of cource without a big change in the phase.Thanks in advance

 

[ariakovo]

If he ever comes back he will hopefully give us more information.

It would nice to know, what exactly he is trying to do with system as a whole.

I made a photo curtain (this is the name in market). 8 infrared proximity sensors.
The problem is that i want to sychronize them. There are two ways. The first is to connect the emitter and the receiver with a wire. The second is to trassmit the frequency. I know how to transimt the frequency and take it back in the receiver but the problem is that i want it to 50% duty cucle but i have to transmite it to 20%.So i take the frequency but i want to change the duty cyle without a big change in the phase.Sorry for not responding.If you have something in mind please post it.Thanks

 

[ariakovo]

He wants a fixed frequency but wants a 50% duty-cycle.

Then maybe a CD4047 IC should be used. It has an oscillator with one resistor and oune capacitor. It has a digital divide-by-two to give a perfect 50% duty cycle. It has two outputs with one inverter if it is needed.

No fixed frequency.I have a frequency and i want to change only the duty cycle.I can't make the frequency again.Please read my posts to others

 

[ariakovo]

Will the frequency be changing? If so, at what rate?

No the frequency remains the same and the duty cycle is 20%.I want to change it in 50%.Not to make the circuit again because i want to transimt the frequency and then to sych

 

[3v0]

Can you transmit a 300Hz signal and use a divide by 2 bistable as suggested by Erick in the 3rd post ?

EDIT: You may have to rig the circuit to ensure they were in phase if you had a divide circuit at each IR unit. Is that why you did not like the idea?

Maybe a better question is why you are forced to XMIT a 20% duty cycle when you need a 50% ?

 

[ariakovo]

Can you transmit a 300Hz signal and use a divide by 2 bistable as suggested by Erick in the 3rd post ?

EDIT: You may have to rig the circuit to ensure they were in phase if you had a divide circuit at each IR unit. Is that why you did not like the idea?

Maybe a better question is why you are forced to XMIT a 20% duty cycle when you need a 50% ?

Ok I start to understand. The problem is that I have to make a long transition and I can't have 50% duty cycle in the emitter (too much current).The best I can give for this is 20% or less. I use 4% or 5% duty cycle for the other ireds. I will transmit 300Hz and then I will use a divider but I don't know any circuit: divide by 2 bistable. So if you know any circuit or an IC that does this work I will be glad. Thank you

 

[MrAl]

Hi,

Are you familiar with any TTL or CMOS ic chips, such as flip flops?

 

[ariakovo]

Hi,

Are you familiar with any TTL or CMOS ic chips, such as flip flops?

Sorry. feel like a stupid. I am working on it. I will use flip flop or a counter. Thanks again.

 

[KMoffett]

How precise and accurate does the 50% duty cycle have be? I don't recall you saying. If the frequency is unchanging, how about a monostable with a period of 1/2 the period of your transmit frequency, triggered by the leading edge of your 20% pulse. 3.33333mS for your 150Hz frequency signal.

Or, is there something else I'm missing.

Ken

 

[ericgibbs]

How precise and accurate does the 50% duty cycle have be? I don't recall you saying. If the frequency is unchanging, how about a monostable with a period of 1/2 the period of your transmit frequency, triggered by the leading edge of your 20% pulse. 3.33333mS for your 150Hz frequency signal.

Or, is there something else I'm missing.

Ken

hi Ken,
I think he also wants to vary the original freq from the 555 with the 20/80%.

 

[KMoffett]

No the frequency remains the same and the duty cycle is 20%....

It may be a language problem, but it looks like the frequency remains unchanged...but ?????

Ken

 

[Roff]

Ariakovo, how do you transmit information with constant frequency and constant duty cycle? Are you turning it on and off?

 

[ariakovo]

Ariakovo, how do you transmit information with constant frequency and constant duty cycle? Are you turning it on and off?

I use a simple ired that I transit the fisrst signal and then I use the TSOP2240 to take it back see second signal.So I have to send it in duty cycle 20% and take it in duct cycle 80%.But for the synch I need the same frequency I transmit (or the divided frequency by a factor) but in 50% duty cycle.