mmajid
Newbie level 4
frequency division and duty cycle
I need a circuit capable of producing square wave signals (0 to +5V pulses)
with some fixed frequencies like 30,20,15,10,5,1 MHZ
(the exact value of them is not so important, for example 9 ~ 11 MHZ
is acceptable instead of 10MHZ ).
I found the attached schematic on the web.the circuit produces square wave pulses
by means of a 1MHZ crystal oscillator based on 4584(IC1 in the schematic), and then
successively divides the frequency by 10 by means of a 4017(IC2~8 in the schematic),
and obtains 100k,10k,1k,100,10,1Hz square pulses.
I had tried to use this circuit for my purpose, but the problem was that the maximum
input frequency for 4584 is about 2 MHZ.
because 74HC4017 supports high frequencies( >50MHZ ),can I replace 4584 based crystal
oscillator with a single 33MHZ oscillator (DIP TTL compatible +5V oscillator) and
then feed the oscillator signal to 4017 to obtain square wave pulses whith frequcies
like 33/2, 33/3,...33/10 MHZ ?
The other problem is that 74HC4017 lowers the duty cycle of the output pulse by the
same factor that lowers the frequency.How can I turn back the duty cycle of the
output to the 50% level?
The other question is that what can I do for 1/4, 1/6, 1/8 outputs.How can I turn back
the duty cycle of them to the 50% level?
It has been mensioned on the phillips 74HC4017 datasheet (the attached paragraph)
that the output pulse withs (duty cycle) can be increased by inserting a RC circuit
on the MR input(PIN 15) of the 4017.How it can do this job, and what specifications
it must have? Can you draw the schematic of such a circuit?
On this schematic we can see that the MR pin is connected to a ouput pin.I think
that this will reset the counters successively.what will be the effect of it
on the output?
Because my knowledge of electronics is very limited, can everybody help me by very simple
terms or drawing schematics or refering to somewhwer on the web (for free schematics).
I will be very very pleased if you can help me in this way.
Hi dear ljox
thank you very much for your reply and schematic.
but you dont said me that if I can use a DIP 33MHZ oscillator(instead of a crystal based
RC osillator+ 4584) and a 4017 to obtain the desired frequencies or not?
The other question is that what can I do for 1/4, 1/6, 1/8 outputs.How can I turn back
the duty cycle of them to the 50% level?
It has been mensioned on the phillips 74HC4017 datasheet (the attached paragraph)
that the output pulse withs (duty cycle) can be increased by inserting a RC circuit
on the MR input(PIN 15) of the 4017.How it can do this job, and what specifications
it must have? Can you draw the schematic of such a circuit?
On this schematic we can see that the MR pin is connected to a ouput pin.I think
that this will reset the counters successively.what will be the effect of it
on the output?
I need a circuit capable of producing square wave signals (0 to +5V pulses)
with some fixed frequencies like 30,20,15,10,5,1 MHZ
(the exact value of them is not so important, for example 9 ~ 11 MHZ
is acceptable instead of 10MHZ ).
I found the attached schematic on the web.the circuit produces square wave pulses
by means of a 1MHZ crystal oscillator based on 4584(IC1 in the schematic), and then
successively divides the frequency by 10 by means of a 4017(IC2~8 in the schematic),
and obtains 100k,10k,1k,100,10,1Hz square pulses.
I had tried to use this circuit for my purpose, but the problem was that the maximum
input frequency for 4584 is about 2 MHZ.
because 74HC4017 supports high frequencies( >50MHZ ),can I replace 4584 based crystal
oscillator with a single 33MHZ oscillator (DIP TTL compatible +5V oscillator) and
then feed the oscillator signal to 4017 to obtain square wave pulses whith frequcies
like 33/2, 33/3,...33/10 MHZ ?
The other problem is that 74HC4017 lowers the duty cycle of the output pulse by the
same factor that lowers the frequency.How can I turn back the duty cycle of the
output to the 50% level?
The other question is that what can I do for 1/4, 1/6, 1/8 outputs.How can I turn back
the duty cycle of them to the 50% level?
It has been mensioned on the phillips 74HC4017 datasheet (the attached paragraph)
that the output pulse withs (duty cycle) can be increased by inserting a RC circuit
on the MR input(PIN 15) of the 4017.How it can do this job, and what specifications
it must have? Can you draw the schematic of such a circuit?
On this schematic we can see that the MR pin is connected to a ouput pin.I think
that this will reset the counters successively.what will be the effect of it
on the output?
Because my knowledge of electronics is very limited, can everybody help me by very simple
terms or drawing schematics or refering to somewhwer on the web (for free schematics).
I will be very very pleased if you can help me in this way.
Hi dear ljox
thank you very much for your reply and schematic.
but you dont said me that if I can use a DIP 33MHZ oscillator(instead of a crystal based
RC osillator+ 4584) and a 4017 to obtain the desired frequencies or not?
The other question is that what can I do for 1/4, 1/6, 1/8 outputs.How can I turn back
the duty cycle of them to the 50% level?
It has been mensioned on the phillips 74HC4017 datasheet (the attached paragraph)
that the output pulse withs (duty cycle) can be increased by inserting a RC circuit
on the MR input(PIN 15) of the 4017.How it can do this job, and what specifications
it must have? Can you draw the schematic of such a circuit?
On this schematic we can see that the MR pin is connected to a ouput pin.I think
that this will reset the counters successively.what will be the effect of it
on the output?
