Programmable Duty Cycle Generation

Thread Starter

winzo

Joined Feb 16, 2009
3
Hi All,

I'm looking for a programmable (serial or parallel) chip that can generate a duty cycle 0-100%, sourced by a 3 or 5 V supply. The tricky part is I need a low freq range: 1-30Hz. This output will be strobing the FSELECT pin of an AD9832 for FSK.

I looked at the MC8640 but it seemed way too advanced. Any suggestions?
 

Thread Starter

winzo

Joined Feb 16, 2009
3
I looked into using a PIC microcontroller, but from what I could figure, none could generate PWM signals at that low a frequency (1-30Hz).

But a microcontroller solution just seems like overkill. Is there anything that I can load a few words into from a serial connection, and it will generate a waveform at a certain % duty cycle, at a certain frequency? If it needs to be externally clocked, that is doable as well...
 

jpanhalt

Joined Jan 18, 2008
11,087
The 12-series PICs in 8-pin packages run with almost no peripheral components. You generate the PWM in software, not the CCP/PWM packages they may come with. Make high, delay1, make low, delay2, and so forth. It's hardly overkill today. One might even argue that by comparison, PWM using a discrete component, like an NE555 is overkill in that application. If you need more accuracy, you can always and easily use a crystal or resonator.

John
 

italo

Joined Nov 20, 2005
205
there is no such a thing as 0% duty cycle or 100% duty cycle. So unless you change your question to something that is possible then I may help you.
 

KMoffett

Joined Dec 19, 2007
2,918
there is no such a thing as 0% duty cycle or 100% duty cycle. So unless you change your question to something that is possible then I may help you.
Interesting! What's your reasoning there? I can make an 8-pin PICAXE 08M microcontroller PWM from full OFF (0% duty cycle) to full ON (100% duty cycle) or anywhere in between. I can easily do a slow 1 to 30HZ PWM. Two pots for two ADC inputs..FREQ and DUTY. One logic level PWM output. Programming in BASIC. Component wise it doesn't get much simpler.

Ken
 

Thread Starter

winzo

Joined Feb 16, 2009
3
I used a 555 in prototyping, but I needed something programmable because I can't swap R/C in my final version.

So I'm going with the PIC12F683. Thanks for the help everyone!
 
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