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Richard Erlacher
02/29/12 20:12
Read: 1011 times
Denver, Co
USA


 
#186309 - Yes ... but ...
Responding to: Daniel Contarino's previous message
He said "... frequency input 1Hz to 70Hz frequency output 10Hz to 700Hz..." with no indication of why a multiplication by 10 is needed for his task of displaying the frequency. He did indicate that the input is AC, but that he can convert it to pulse format.

Now, I'm not clear as to why he needs the frequency multiplier. 10 Hz is quick enough that, when divided by 10 it will give meaningful and readable information. Since the input is in the range 10 to 70 Hz, he could easily detect zero crossings, or peaks in the AC waveform, very possibly a sinusoid, and time the interval between them. That would provide good data as to the frequency.

Accumulating phase error between a local VCO and an input waveform would take quite a bit of time and to acquire lock would require probably on the order of 32 cycles, but because it's such a slow rate, doing it in firmware would be easy enough. That, again, requires timers, but you have them in an 805x, and extending them in firmware is straightforward.

I'd recommend he examine various PLL options, e.g. the all-digital PLL application of the 74HC297. Those two clocks used by that device can be generated in firmware and don't even have to leave the MCU, yet can be applied in the exact way the '297 does it. Then, if he decided he needs to use a multiplier to update his display, he can do that. I'd guess that he can divide his input clock by 10 and still arrive at a useful speed indicator.

RE




List of 52 messages in thread
TopicAuthorDate
frequency multiplier x 10      Mahmood Elnasser      02/20/12 14:29      
   You need some specs first.      Michael Karas      02/20/12 19:56      
      and even more questions for your tutor        Jim Granville      02/21/12 12:42      
   Analog solution...      Kai Klaas      02/21/12 05:49      
      Input wave form      Per Westermark      02/21/12 06:09      
      Too Bad...      Michael Karas      02/21/12 06:16      
   have you considered a "rate multiplier"?      Richard Erlacher      02/21/12 08:18      
   PCA?      Erik Malund      02/21/12 12:51      
      PCA Yes      Michael Karas      02/21/12 15:38      
   Update      Mahmood Elnasser      02/22/12 00:43      
      2 i.c.s plus 6 R, C      David Prentice      02/22/12 03:03      
      4046 / 7490      Michael Karas      02/22/12 03:36      
      I put my bet in the digital solution      Daniel Contarino      02/22/12 13:33      
         digital solution      Mahmood Elnasser      02/22/12 13:46      
            MCU / CPLD      Michael Karas      02/22/12 13:57      
            Simple digital solution...      Kai Klaas      02/23/12 05:59      
               Engine too fast      Mahmood Elnasser      02/23/12 06:48      
                  it could be made simpler        Jim Granville      02/29/12 19:22      
                     cute      Erik Malund      03/01/12 08:07      
               OR      Erik Malund      02/23/12 06:52      
   Frequency Multipiler      Satish S Munot      02/29/12 10:06      
      Motivation?      Per Westermark      02/29/12 10:14      
         Motivation ?????????      Satish S Munot      02/29/12 10:55      
            Motives      Per Westermark      02/29/12 11:24      
               OK      Satish S Munot      02/29/12 12:40      
                  motivation guess      Maarten Brock      03/02/12 01:14      
                     I had the same feeling...      Kai Klaas      03/02/12 08:25      
                        and if you looked at any of his previous posts ...      Richard Erlacher      03/02/12 20:02      
   A number of thins concern me ...      Richard Erlacher      02/29/12 12:31      
      answers      Mahmood Elnasser      02/29/12 14:45      
      Boring...      Kai Klaas      02/29/12 16:05      
         And in this case...      Daniel Contarino      02/29/12 18:11      
            Yes ... but ...      Richard Erlacher      02/29/12 20:12      
               Making what you need, from what you can get..      Jim Granville      02/29/12 22:14      
                  slogans      Satish S Munot      02/29/12 23:59      
                  Is that what the display needs?      Richard Erlacher      03/01/12 06:38      
                     10-700 Hz is expected output frequency - not input frequency      Per Westermark      03/01/12 06:57      
                        I did make one mistake      Richard Erlacher      03/01/12 07:18      
                           old rpm analog (or digital) display is what they have      Jim Granville      03/01/12 12:01      
                              bursts...      Kai Klaas      03/01/12 13:19      
                                 See LM2917 for ancient tacho examples      Jim Granville      03/01/12 13:40      
   PLL      Mahmood Elnasser      03/18/12 06:57      
   More detail?      Richard Erlacher      03/18/12 12:30      
      Yes, more details, please...      Kai Klaas      03/18/12 12:43      
         Details      Mahmood Elnasser      03/31/12 00:24      
            This can have to do ...      Kai Klaas      03/31/12 09:25      
               sharp edges      Mahmood Elnasser      04/01/12 03:59      
                  Which phase-detector?      Richard Erlacher      04/01/12 08:21      
               re: this can have      Andy Peters      04/02/12 10:49      
                  What I would do...        Kai Klaas      04/03/12 07:40      
                     Very Low Frequency      Mahmood Elnasser      04/19/12 15:30      
                        Give it a try...      Kai Klaas      04/19/12 17:14      

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