Post by thread:[PIC]: Frequency multiplier?

> I've got a variable frequency signal (200hz to 4khz) whose frequency I want > to increase by 30% (5v signal). IE if the input frequency is 1000hz, I > want to output 1300hz. Is there an easy method of doing this? I've heard > of PLL, but don't have a clue how to build them, so if there's an easier > option that would be great. > > Gary It depends on what you need to do with the signal. If the resulting output signal can have significant jitter, and unequal size cycles then this job can easily be done with a single component: an 8-pin PIC. If you need to keep a 'square wave' output then it gets a little trickier, but can still be done in a small PIC. Just to give you an idea of how you could do it if jitter and output cycle size don't matter: ; ===================== ; The main loop. Each iteration of this loop processes ten ; cycles of the input signal (in the copypulse routine). Three of ; those cycles are doubled by calling the outpulse routine ; to send an extra pulse in the low portion of the input ; pulse. mainloop: call copypulse call copypulse call copypulse call outpulse call copypulse call copypulse call copypulse call outpulse call copypulse call copypulse call copypulse call outpulse call copypulse goto mainloop ; ===== copy an input pulse to the output pin ====== copypulse: ; look for the rising edge waithi: btfss INPUT goto waithi btfss INPUT goto waithi ; we just saw a rising edge, copy it to the output bsf OUTPUT ; wait for the input to go low again waitlo: btfsc INPUT ; wait for input to be low goto waitlo btfsc INPUT ; check twice to protect against glitches goto waitlo ; we just saw a falling edge, copy it to the output bcf OUTPUT retlw 0 ; ===== output an extra pulse ===== ; ; At 4Hz (the maximum input frequency) the low level during ; which we have to output our extra pulse lasts for 1/8000 ; of a second. We have to fit a low-high-low into that time ; to fit our pulse in. To allow for input jitter and modest ; overfrequency we'll set the time for the first low and high ; to about 1/32000 of a second outpulse: ; output low for 1/32000 of a second call delay ; delay 1/32000 ; output high for the next 1/32000 bsf OUTPUT call delay ; output low until the next pulse bcf OUTPUT retlw 0 Bob Ammerman RAm Systems -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Since you put this as the [PIC] topic, I'm going to invent a PIC solution for this, which I haven't tried, but thinking should be doable... Measure the low-time and high-time of the first pulse, then generate pulses at 130% the frequency of that ..... repeatedly in a loop. While that's happening, in a sort of feedback mechanism, count both input and output pulses and adjust accordingly by offsetting the next pulse(s). This method should provide low jitter, but would add a small (approx 1/2 to 1-pulse) delay from input to output, and depending on the actual coding, may introduce a limitation on how fast the output will follow the input on freq change. Of course this is not totally trivial, but it should be doable with any simple PIC. Cheers, -Neil. On Wednesday 23 April 2003 20:08, Gary Neal wrote: {Quote hidden}> Hi, > > I've got a variable frequency signal (200hz to 4khz) whose frequency I want > to increase by 30% (5v signal). IE if the input frequency is 1000hz, I > want to output 1300hz. Is there an easy method of doing this? I've heard > of PLL, but don't have a clue how to build them, so if there's an easier > option that would be great. > > Thanks, > > Gary -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> I've got a variable frequency signal (200hz to 4khz) whose frequency I > want to increase by 30% (5v signal). IE if the input frequency is > 1000hz, I want to output 1300hz. Is there an easy method of doing > this? I've heard of PLL, but don't have a clue how to build them, so > if there's an easier option that would be great. A PLL (Phase Locked Loop) could be a solution. If you don't have a clue about them, then learn or get someone else to do the design. There's got to be loads of material out there on PLLs, so I won't repeat most of it here. Basically, you can use a PLL to multiply a frequency by a rational number. However, things get more tricky as the integers get larger and the frequency range ratio gets wider. Depending on response speed, a PIC might be another solution. You could use a CCP module in capture mode to determine the incoming period, then use PWM output to produce a signal with .77 of the input period. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

pic microcontroller discussion list <> wrote on Thursday, April 24, 2003 12:57 PM: > A PLL (Phase Locked Loop) could be a solution. If you don't have a > clue about them, then learn or get someone else to do the design. > There's got to be loads of material out there on PLLs, so I won't There is loads of material. Unfortunately much of it is quite confusing, at least to me... with arbitrary 2*pi appearing in some app notes etc, and not in others, and contradictory advice on choosing the right phase comparator for best performance. The PLL section in Horowitz & Hill is still the plainest advice I've come across on the subject, it's nice to see books still have value :-) I've produced a PLL circuit for a low speed noisy FSK comms link. It works, but I can't help thinking it should work better, the VCO signal needs quite a lot of post-filtering to get reliable data out. If anyone has any good pointers on FSK demodulation, choosing the right phase comparator and loop filter design, I'd love to hear them- the FSK is a couple of kHz, data rate a few 10's of bps. The principle is easy to understand, and it sounds like the 'right' solution for the OP's problem, but the practicalities seem more complex. I know it's not just me, I've never met anyone who claims to be expert in PLLs in Real Life(TM), and only a few who claim to be, online... Nigel -- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Looking at the question as inputting a signal with a 50% duty cycle and outputting a signal 130% greater with a 50% duty cycle, here is my solution. Requires 4 routines, count input pulse width see if input changed decrement output count see if time to change output COUNT INPUT PULSE WIDTH In order to get the increase in frequency, the input count must be reduced before it becomes the count for the output. This is done by not counting the input pulse every forth time. The 'fourth input counter' will add a count to the input count to 'tweak it from 125% to 130% every 13th time it is called. The 52 (4*13) input timings results in 39 (3*13) input counts, and if 1 input count is added at this time, the percentage of 40 counts to 52 timings is 130%. SEE IF INPUT CHANGES When the input state changes, the input count is moved to the 'last pulse count' and the input pulse count is cleared. It may be a good idea to average the last pulse count and input pulse instead of just moving it. This is easily done by adding the two and right shifting the results. This averaging will encourage a 50% duty cycle for the output pulses. DECREMENT OUTPUT COUNT Just subtract one from output count. SEE IF TIME TO CHANGE OUTPUT if output count is zero, toggle output pulse and move 'last pulse count' to output count So there would be three series of count input pulse width see if input changed decrement output count see if time to change output And a fourth series with the 'count input pulse width' modified to only counting every 13th time. One main concept is that the input pulse and output pulse have no relationship in time except the 'last pulse count', and that count can change any time with the output routine using it when it toggles the output pulse and starts a new pulse. Bill {Original Message removed}

Great, very simple, very good. Bill ----- Original Message ----- From: "Rychta Bretislav" <spam_OUTBretislavRychtaTakeThisOuTALVISHAGGLUNDS.SE> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Monday, April 28, 2003 11:48 PM Subject: SV: [PIC]: Frequency multiplier? The better way is to add 10 to input count and subtract 13 from output count. When output count underflow, toggle output pulse and ADD 'last pulse count' to output count. This approach don't need any further correction and allow you to easy change ratio of input and output frequency by changing only 2 constants. Run sequence on interrupt from timer to get constant sampling frequency which is in your case higher than 2*4000*13/10 Hz and lower than 2*200*65536/10 Hz (for 2-Byte counters) Breta -----Ursprungligt meddelande----- Fren: Bill & Pookie [williamcornutt111KILLspamATTBI.COM] Skickat: mendag 28 april 2003 16:05 Till: .....PICLISTKILLspam.....MITVMA.MIT.EDU Dmne: Re: [PIC]: Frequency multiplier? Looking at the question as inputting a signal with a 50% duty cycle and outputting a signal 130% greater with a 50% duty cycle, here is my solution. Requires 4 routines, count input pulse width see if input changed decrement output count see if time to change output COUNT INPUT PULSE WIDTH In order to get the increase in frequency, the input count must be reduced before it becomes the count for the output. This is done by not counting the input pulse every forth time. The 'fourth input counter' will add a count to the input count to 'tweak it from 125% to 130% every 13th time it is called. The 52 (4*13) input timings results in 39 (3*13) input counts, and if 1 input count is added at this time, the percentage of 40 counts to 52 timings is 130%. SEE IF INPUT CHANGES When the input state changes, the input count is moved to the 'last pulse count' and the input pulse count is cleared. It may be a good idea to average the last pulse count and input pulse instead of just moving it. This is easily done by adding the two and right shifting the results. This averaging will encourage a 50% duty cycle for the output pulses. DECREMENT OUTPUT COUNT Just subtract one from output count. SEE IF TIME TO CHANGE OUTPUT if output count is zero, toggle output pulse and move 'last pulse count' to output count So there would be three series of count input pulse width see if input changed decrement output count see if time to change output And a fourth series with the 'count input pulse width' modified to only counting every 13th time. One main concept is that the input pulse and output pulse have no relationship in time except the 'last pulse count', and that count can change any time with the output routine using it when it toggles the output pulse and starts a new pulse. Bill ----- Original Message ----- From: "Gary Neal" <EraseMEgln103spam_OUTTakeThisOuTPSU.EDU> To: <PICLISTspam_OUTMITVMA.MIT.EDU> Sent: Wednesday, April 23, 2003 6:08 PM Subject: [PIC]: Frequency multiplier? > Hi, > > I've got a variable frequency signal (200hz to 4khz) whose frequency I want > to increase by 30% (5v signal). IE if the input frequency is 1000hz, I > want to output 1300hz. Is there an easy method of doing this? I've heard > of PLL, but don't have a clue how to build them, so if there's an easier > option that would be great. > > Thanks, > > Gary > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

What if the duty cycle is not 50%, and say variable? RA ----- Original Message ----- From: "Bill & Pookie" <@spam@williamcornutt111KILLspamATTBI.COM> To: <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> Sent: Tuesday, April 29, 2003 12:57 PM Subject: Re: [PIC]: Frequency multiplier? {Quote hidden}> Great, very simple, very good. > > Bill > > ----- Original Message ----- > From: "Rychta Bretislav" > <RemoveMEBretislavRychtaTakeThisOuTALVISHAGGLUNDS.SE> > To: <spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU> > Sent: Monday, April 28, 2003 11:48 PM > Subject: SV: [PIC]: Frequency multiplier? > > > The better way is to add 10 to input count and > subtract 13 from output > count. When output count underflow, toggle output > pulse and ADD 'last pulse > count' to output count. > This approach don't need any further correction > and allow you to easy change > ratio of input and output frequency by changing > only 2 constants. > Run sequence on interrupt from timer to get > constant sampling frequency > which is in your case higher than 2*4000*13/10 Hz > and lower than 2*200*65536/10 Hz (for 2-Byte > counters) > > Breta > > -----Ursprungligt meddelande----- > Fren: Bill & Pookie > [TakeThisOuTwilliamcornutt111EraseMEspam_OUTATTBI.COM] > Skickat: mendag 28 april 2003 16:05 > Till: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU > Dmne: Re: [PIC]: Frequency multiplier? > > > Looking at the question as inputting a signal with > a 50% duty cycle and outputting a signal 130% > greater with a 50% duty cycle, here is my > solution. > > Requires 4 routines, > > count input pulse width > see if input changed > decrement output count > see if time to change output > > > COUNT INPUT PULSE WIDTH > > In order to get the increase in frequency, the > input count must be reduced before it becomes the > count for the output. This is done by not > counting the input pulse every forth time. > > The 'fourth input counter' will add a count to the > input count to 'tweak it from 125% to 130% every > 13th time it is called. The 52 (4*13) input > timings results in 39 (3*13) input counts, and if > 1 input count is added at this time, the > percentage of 40 counts to 52 timings is 130%. > > SEE IF INPUT CHANGES > > When the input state changes, the input count is > moved to the 'last pulse count' and the input > pulse count is cleared. It may be a good idea to > average the last pulse count and input pulse > instead of just moving it. This is easily done by > adding the two and right shifting the results. > This averaging will encourage a 50% duty cycle for > the output pulses. > > DECREMENT OUTPUT COUNT > > Just subtract one from output count. > > SEE IF TIME TO CHANGE OUTPUT > > if output count is zero, toggle output pulse and > move 'last pulse count' to output count > > So there would be three series of > count input pulse width > see if input changed > decrement output count > see if time to change output > > And a fourth series with the 'count input pulse > width' modified to only counting every 13th time. > > One main concept is that the input pulse and > output pulse have no relationship in time except > the 'last pulse count', and that count can change > any time with the output routine using it when it > toggles the output pulse and starts a new pulse. > > Bill > > > ----- Original Message ----- > From: "Gary Neal" <gln103EraseME.....PSU.EDU> > To: <EraseMEPICLISTMITVMA.MIT.EDU> > Sent: Wednesday, April 23, 2003 6:08 PM > Subject: [PIC]: Frequency multiplier? > > > > Hi, > > > > I've got a variable frequency signal (200hz to > 4khz) whose frequency I want > > to increase by 30% (5v signal). IE if the input > frequency is 1000hz, I > > want to output 1300hz. Is there an easy method > of doing this? I've heard > > of PLL, but don't have a clue how to build them, > so if there's an easier > > option that would be great. > > > > Thanks, > > > > Gary > > > > -- > > http://www.piclist.com hint: The list server can > filter out subtopics > > (like ads or off topics) for you. See > http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The list server can > filter out subtopics > (like ads or off topics) for you. See > http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The PICList is > archived three different > ways. See http://www.piclist.com/#archives for > details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Tue, 29 Apr 2003, Reinaldo Alvares wrote: > What if the duty cycle is not 50%, and say variable? Any square wave can be made into a 50% duty cycle by dividing by 2. In other words, just watch the rising (or falling) edge. Brata's approach still works. This is just another example of a phase accumulator. I haven't been monitoring this thread too closely, but the easiest way to solve this problem for a single channel is to utilize the PIC's input capture and timer 2 outputs. For example, configure TMR1 to capture all rising edges and PR2 to specify TMR2's period. The value stuffed in PR2 is simply multiplicative (and possibly filtered) factor of the capture interval. The fact that someone hasn't suggested this solution implies that either this is for a PIC without these peripherals or there is more than one channel. [but after reading the original poster's request, it appears that only one channel is required -- so maybe there's another reason.] One way to do this in software is like so: In the (high frequency) interrupt routine: CurrentState = IOPort(); rising_edge = (CurrentState ^ LastState) & CurrentState; LastState = CurrentState; if(rising_edge & BIT_n) { rollover = rising_edge_counter; rising_edge_counter = 0; } else rising_edge_counter++; if(freq_out == 0) { toggle_output(); freq_out = Fout_half_period; } else freq_out--; And in the main loop: if (rollover) { Fout_update_period(); rollover = 0; } Where Fout_update_period() scales the period of the output clock to be a multiplicative factor of the input clock. Or more specifically, the periods are scaled. This rather verbose approach is easily scalable to multiple channels. To monitor the rising edges and control the scaled frequency outputs, then something like this would suitable for a high frequency interrupt (e.g. tmr0 rollovers): movf Input_PORT,W ;Read the current xorwf LastState,W ;compare to the last xorwf LastState,F ;Save current as last andwf LastState,W ;Get the rising edges. movwf temp ; iorwf rollovers,F ;Let the main loop know ; before processing the rollovers, ; generate the outputs (this way you'll be less susceptible to ; the jitter incurred with the non-isochronous code that processes ; the rising edges.) clrf FoutToggle ; assume that the outputs aren't ; going to change movf Fout0_period,W ;Get the (half) period in case we roll decf Fout0_ctr,F ;Toggle when this reaches zero ;Check the rollovers - use btf's instead skpnz ;of goto's for isochronous execution. movwf Fout0_ctr ;rolled over, so reset the counter skpnz ; bsf FoutToggle,0 ;and set this bit for below ... same for other outputs ; now update the outputs movf FoutToggle,W xorwf Fout,W movwf Fout movwf Output_PORT ; now process the rising edges. ch0: incf Ch0_ctr ;Assume rising edge did not occur btfsc temp,0 goto re0 ;Handle the rising edge ch1: ... chn: ... return ; or interrupt exit code re0: decf Ch0_ctr,W ; movwf Ch0_period clrf Ch0_ctr goto Ch1 re1: ... ------------ In the main loop, ch0_period and when it becomes non-zero, update the Fout0_period. Again, this is just a detailed explanation of the phase accumulator alogrithm proposed by Breta. Scott -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Thanks to all for your answers to my 50% stuff question. I perhaps didn't explain myself properly or didn't understand your answer correctly. Let me please rephrase my question. Let's say I want to multiply the frequency of an input square wave by some factor "F".Consider a sensor giving pulses from a rotating shaft, if the shaft accelerates then two consecutive periods are different. Every next period will be shorter than the previous one. Now if I divide the first period "P" by "F" and output an "F" amount of pulses with periods equal to "P/F" then the PIC will still be outputting pulses while the next period is already happening. I can't loose counts since I need this for positioning, direction and speed measurement purposes. I have to watch both edges for any change in the direction of the shaft.The sensor is a quadrature encoder with only A and B outputs, no Z. I have to output two channels out of phase by ~90% to the system processing the data.The phase difference is naturally the same as the incoming pulse. I have managed to do it for a fixed or slow variable frequency.I implemented it in software on an 16F84A, I know they are outdated, but I have lots of them!. When the shaft accelerates fast then I start to miss about 3 to 10% of the pulses depending on the acceleration, getting offsets in position.When the shaft is slowing down then is ok because the next period will be longer. There will be space enough in time to accommodate the multiplied pulses before the next ones will have to be outputted. I might be missing something here, I don't know what a phase accumulator is but I'll try to find out. It looks to me that this task is just not possible to fix on a base of period by period multiplication. I appreciate very much any advise or pointer to how to solve this. And sorry for taking this thread, I didn't mean to. Best regards RA {Original Message removed}

>I implemented it in software on an 16F84A, I know they are >outdated, but I have lots of them!. When the shaft accelerates >fast then I start to miss about 3 to 10% of the pulses >depending on the acceleration, getting offsets in position. I suspect that using any micro is going to cause you problems. I think you may have to resort to something like Direct Digital Synthesis, or a proper phase lock loop system as a minimum. Whatever you do there will be a time lag between the encoder speeding up and your multiplied output catching up, as the multiplier cannot predict when the next edge is going to occur that it will need to measure. Your other problem is going to occur with the lowest rotation rate of the encoder that you wish to lock to. I cannot recall you stating this, but I seriously doubt you will be able to go right down to 0 rpm, and I get the feeling that is what you want to do. When you refer to offsets in position, are you trying to make an x-y plotter or something similar? It seems to me that what you really need to do is get an encoder that has more steps per revolution. Your only other way to option that I can think of is to remove the encoder from its current connection, and have a suitable gearbox between it and the drive shaft to increase the shaft speed into the encoder. One of these two solutions is going to be the only way you will get a satisfactory low speed performance. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

----- Original Message ----- From: "Alan B. Pearce" <EraseMEA.B.PearceEraseMERL.AC.UK> To: <@spam@PICLIST@spam@spam_OUTMITVMA.MIT.EDU> Sent: Wednesday, April 30, 2003 9:45 AM Subject: Re: [PIC]: Frequency multiplier? > >I implemented it in software on an 16F84A, I know they are > >outdated, but I have lots of them!. When the shaft accelerates > >fast then I start to miss about 3 to 10% of the pulses > >depending on the acceleration, getting offsets in position. > > I suspect that using any micro is going to cause you problems. I think you > may have to resort to something like Direct Digital Synthesis, or a proper > phase lock loop system as a minimum. Whatever you do there will be a time > lag between the encoder speeding up and your multiplied output catching up, > as the multiplier cannot predict when the next edge is going to occur that > it will need to measure. That's exactly what I thought until I saw the post here about multiplying a frequency with a PIC. Perhaps it's because the input frequency was fixed and didn't matter a few periods lost for adjustments. Perhaps I missunderstood the whole thing; but I had to ask, this is why this list is for after all. Using DDS was not an option because of the price of those. > > Your other problem is going to occur with the lowest rotation rate of the > encoder that you wish to lock to. I cannot recall you stating this, but I > seriously doubt you will be able to go right down to 0 rpm, and I get the > feeling that is what you want to do. You're right again. The minimum was 0 rpm, and yes I did had to use a time out for that. Otherwise the output pulses would have been way too long. > > When you refer to offsets in position, are you trying to make an x-y plotter > or something similar? It seems to me that what you really need to do is get > an encoder that has more steps per revolution. Your only other way to option > that I can think of is to remove the encoder from its current connection, > and have a suitable gearbox between it and the drive shaft to increase the > shaft speed into the encoder. One of these two solutions is going to be the > only way you will get a satisfactory low speed performance. No is not an x-y plotter.The encoder is on a moving cart with a scanning system on it. The pulses are used to trigger one scan per pulse. The encoder is connected to the shaft of one of the wheels. I used magnets placed on the wheel to trigger an Allegro hall effect sensor with quadrature output. Because of the size of the wheel I could not mount more magnets on it. I used the smallest ones I could found 1mm diameter. The magnets were used because this equipment goes into water, dust and many other tough conditions, where optical systems are difficult to implement. So the end was to get an E4 encoder from USdigital and get a rugged case for it. The whole construction is a cylinder 120mm long and 29mm diameter and solved all the problems. I spent quite a while trying to do the trick with a micro, that's why I was interested in some opinions regarding this. I guess from the beginning it was a doomed project. Anyway, I always try to listen to other people because one can never learn to much. Thanks a lot for your time. RA > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email spamBeGonelistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

{Quote hidden}> -----Original Message----- > From: Reinaldo Alvares [SMTP:TakeThisOuTreinaldoalvares.....TakeThisOuTTELIA.COM] > Sent: Wednesday, April 30, 2003 9:22 AM > To: TakeThisOuTPICLISTKILLspamspamMITVMA.MIT.EDU > Subject: Re: [PIC]: Frequency multiplier? > No is not an x-y plotter.The encoder is on a moving cart with a scanning > system on it. The pulses are used to trigger one scan per pulse. The > encoder > is connected to the shaft of one of the wheels. I used magnets placed on > the > wheel to trigger an Allegro hall effect sensor with quadrature output. > Because of the size of the wheel I could not mount more magnets on it. I > used the smallest ones I could found 1mm diameter. The magnets were used > because this equipment goes into water, dust and many other tough > conditions, where optical systems are difficult to implement. So the end > was > to get an E4 encoder from USdigital and get a rugged case for it. The > whole > construction is a cylinder 120mm long and 29mm diameter and solved all the > problems. I spent quite a while trying to do the trick with a micro, > that's > why I was interested in some opinions regarding this. I guess from the > beginning it was a doomed project. Anyway, I always try to listen to other > people because one can never learn to much. > Thanks a lot for your time. > Perhaps consider a reluctance sensor, as used on engine managment systems for engine position sensing? This way all you need on the rotating part is a ferrous toothed wheel which should give you considerably better resolution. You can use two reluctance sensors to give a quadrature output if needed. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to .....postmasterRemoveMEbookham.com. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

On Wed, 30 Apr 2003, Reinaldo Alvares wrote: {Quote hidden}> Thanks to all for your answers to my 50% stuff question. > I perhaps didn't explain myself properly or didn't understand your answer > correctly. > Let me please rephrase my question. Let's say I want to multiply the > frequency of an input square wave by some factor "F".Consider a sensor > giving pulses from a rotating shaft, if the shaft accelerates then two > consecutive periods are different. Every next period will be shorter than > the previous one. Now if I divide the first period "P" by "F" and output an > "F" amount of pulses with periods equal to "P/F" then the PIC will still be > outputting pulses while the next period is already happening. I can't loose > counts since I need this for positioning, direction and speed measurement > purposes. I have to watch both edges for any change in the direction of the > shaft.The sensor is a quadrature encoder with only A and B outputs, no Z. I > have to output two channels out of phase by ~90% to the system processing > the data.The phase difference is naturally the same as the incoming pulse. I > have managed to do it for a fixed or slow variable frequency.I implemented > it in software on an 16F84A, I know they are outdated, but I have lots of > them!. When the shaft accelerates fast then I start to miss about 3 to 10% > of the pulses depending on the acceleration, getting offsets in > position.When the shaft is slowing down then is ok because the next period > will be longer. There will be space enough in time to accommodate the > multiplied pulses before the next ones will have to be outputted. I might be > missing something here, I don't know what a phase accumulator is but I'll > try to find out. It looks to me that this task is just not possible to fix > on a base of period by period multiplication. I appreciate very much any > advise or pointer to how to solve this. And sorry for taking this thread, I > didn't mean to. Okay. There are two pieces of information that are being manipulated. There's the frequency *and* there's the pulse width. The phase accumulator approach can still be made to work. The job would be *so* much easier to accomplish with a better endowed PIC than the lowly f84... 1) Measure the input period, i.e. time between rising edges 2) Measure the input pulse width, i.e. time between a rising and falling edge. 3) Scale the input period and input frequency to produce the output period and frequency. The hard part (with an f84) is sampling the signals fast enough. Here are some snippets to help: Edge detector: movf IOPORT,w ;sample the incoming signal xorwf last_sample,w ;compare to the last sample andlw IOBIT ; skpnz ;If they're the same then no need to goto no_change ;process xorwf last_sample,f ;Save this sample for next time andwf last_sample,W ;Is this a rising edge? skpnz goto falling_edge rising_edge: ... goto no_change falling_edge: ... no_change: ------------------ Now to generate the scaled pulse output, I'd use phase shifted counters: http://www.dattalo.com/technical/theory/pwm.html The periods of the rising and falling edge counters are the same and equal the scaled frequency output. The relative phase shift corresponds to the desired pulse width. See http://www.dattalo.com/technical/software/pic/pwm8.asm for example of 8 parallel PWM outputs that use this technique. For a single channel, there several optimizations one could make. Scott -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistserv@spam@spam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Reinaldo, One on-the-side question ... I remember you stating that this was on a cart of some type with a 29mm diameter wheel, and one sensor on the wheel. You also mentioned 1khz max input rate. 29mm dia ~= 91mm circumference. At 1000 khz with one sensor (which means 1000 rpm), this means 91000 mm per sec, or approx 328 km per hour...!? Are you sure that the assumptions are realistic? Having a buffer is a great idea, but this may be pushing it a bit I think. Either I messed up with the math, read something wrong, am assuming something incorrect, or ... ? Cheers, -Neil. On Friday 02 May 2003 00:38, Reinaldo Alvares scribbled: > Thanks to everyone for your suggestions, very interesting and educational. > I'll give a try to this problem again to see if I can get any useful > results. As Alan B. Percy and Ben Jackson pointed out there's always going > to be some error in the output pulses. The question is, whether I can get > the error to be low or not. I think some 1 to 3% would be ok, so I'll try > the suggestions from Picdude and Scott Dattalo and see what's going to > happen. And sorry for my late reply, here in Sweden yesterday was a free > day at work. > Best regards > RA > {Original Message removed}