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frequency to duty cycle

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charles767

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i have a rectangular wave with variable frequency,

how can i obtain a wave with variable duty cycle?

regards
Charles
 
Do you mean you want to convert the variable frequency signal to one with constant frequency, and a duty cycle that varies as a function of the frequency of the input signal? If so, you have to specify the frequency range of the input signal, and the desired frequency of the output. Voltage amplitudes also need to be specified.
 
or do you want to have a seperate divice to give you variable duty cycle with fixed frequency or with variable frequency? you want to design a circuit? or you need to find out some ready made boards? or want to get it from what you have?
 
I have a input signal (rectangular wave) with variable frequency.

i search a circuit that have like output signal a constant frequency and a duty cycle that varies as a function of the frequency of the input signal.

range input [0, 4kHz]
The frequency of the output for example 1kHz but i must can change it.
the voltage amplitude for example 1V but i must can change it.
 
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there are number of circuits you can find on net for changing duty cycle by applying/ varying a voltage using a pot, or etc. its basically a PWM. what else you have to do with is to have a frequency to voltage convertor and then feed it to the PWM circuit.
 
see the attached pic of Freq. to voltage converter and voltage controlled pulse width generator, you may need a squire wave input to complete it. some one has posted a circuirt for PWM with variable frequency in a different post. it also can be usefull with slight modification. you have to combine all in good way to get your accuracy.
 

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I need what he needs also, I think.

I'm looking to have a variable frequency square wave, pulsed on the negative side as the input.

the output frequency needs to match the input frequency, but vary the pulse width output in a linear fashion with the frequency input.

and have an adjustment knob that would set the pulse width for fine tuning, from zero pulse width at zero frequency to 100% pulse width at 5khz (preferable 5 knobs that would each target a set frequency range, yet all work together at the same time), all voltages need to operate from 10-15v and the output needs to be able to power up to 8 small 12v solenoids...

I'm willing to pay a tiny bit for a working diagram...
 
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Your help said that i need two block:

block 1 ) Freq. to voltage converter
and
block 2 ) voltage controlled pulse width generator

but in the two circuit to change the voltage (block 1) and to change the duty cycle (block 2) there are variable resistors.

i have a rectangular wave with variable frequency,

changing the frequency of the input signal should vary the duty cycle of rectangular wave output.
 
If you feed block 1 into block 2, that will do what you want. The variable resistors are to customize the circuit for the actual frequencies you need.
 
I need what he needs also, I think.

I'm looking to have a variable frequency square wave, pulsed on the negative side as the input.

the output frequency needs to match the input frequency, but vary the pulse width output in a linear fashion with the frequency input.

and have an adjustment knob that would set the pulse width for fine tuning, from zero pulse width at zero frequency to 100% pulse width at 5khz (preferable 5 knobs that would each target a set frequency range, yet all work together at the same time), all voltages need to operate from 10-15v and the output needs to be able to power up to 8 small 12v solenoids...

I'm willing to pay a tiny bit for a working diagram...

That's a very easy one Joe. To get 100% pulse width at 5kHz you need a fixed high pulse time of 200uS.
At 2.5kHz that same fixed high pulse time of 200uS gives you 50% duty, so it is linear.

All you need is a 555 timer circuit or equivalent that makes a fixed 200uS high time pulse for every input pulse.
 
since you need zero width at zero Hz,
achiving pulse widh from ZERO may not be possible, it may have a limitation depends on the response time of the components used. but from a reasonably narrow width to a certain value can be possible.

also when you increase the frequency, it put limitation on the pulse width. if you work on duty cycle instead it will make good value.

or you can inverse your idea to have zero width when high frequency and increase it when frequency comes down.

you should start working on paper and decide the ranges and all before you customise you circuit.
 
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