Post by thread:[PIC]: 10 PWM outputs on PIC16F874

Hi, I need to control 10 DC motors using DC Voltage control. Can this be done in Software PWM Only. Any Ideas. Another point is that the motors will all be operated in 4 discrete steps off, low, medium, high. If this is so does it simplify things. What frequency of PWM would be good for DC Motor control The motors are small motors taking about 100ma at 13.6 Volts DC rgds ramana -- 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

>What frequency of PWM would be good for DC Motor control The motors are >small motors taking about 100ma at 13.6 Volts DC This depends on the core of the motor. If the motor has an iron core, then a reasonably low frequency needs to be used. If the motor is a coreless type (Falhauber or similar, also known as a bell wound armature) then the frequency needs to be quite high, of the order of 20kHz. If you really want to chase the differences , try a model railroading list which has details of DCC decoders for electronic control. -- 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

----- Original Message ----- From: Ramana <spam_OUTramanabvTakeThisOuTDANLAWINC.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Wednesday, August 23, 2000 7:47 AM Subject: Re: [PIC]: 10 PWM outputs on PIC16F874 > Hi, I need to control 10 DC motors using DC Voltage control. Can this be > done in Software PWM Only. Any Ideas. Sure. Try using 'vertical math'. > Another point is that the motors will all be operated in 4 discrete > steps > off, low, medium, high. If this is so does it simplify things. This means you can probably use a relatively poor resolution in your PWM. I would _not_ expect to get away with a resolution of just 4 equal-sized intervals however. > What frequency of PWM would be good for DC Motor control The motors are > small motors taking about 100ma at 13.6 Volts DC The lowest you can get away with given the fact that you want to bit bang ten of these. > rgds > ramana > > -- > 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

Hello, May I know what "Try using 'vertical math'" is. thanks ramana -----Original Message----- From: Bob Ammerman [RAMMERMANKILLspamPRODIGY.NET] Sent: Wednesday, August 23, 2000 5:36 PM To: .....PICLISTKILLspam.....MITVMA.MIT.EDU Subject: Re: [PIC]: 10 PWM outputs on PIC16F874 ----- Original Message ----- From: Ramana <EraseMEramanabvspam_OUTTakeThisOuTDANLAWINC.COM> To: <PICLISTspam_OUTMITVMA.MIT.EDU> Sent: Wednesday, August 23, 2000 7:47 AM Subject: Re: [PIC]: 10 PWM outputs on PIC16F874 > Hi, I need to control 10 DC motors using DC Voltage control. Can this be > done in Software PWM Only. Any Ideas. Sure. Try using 'vertical math'. > Another point is that the motors will all be operated in 4 discrete > steps > off, low, medium, high. If this is so does it simplify things. This means you can probably use a relatively poor resolution in your PWM. I would _not_ expect to get away with a resolution of just 4 equal-sized intervals however. > What frequency of PWM would be good for DC Motor control The motors are > small motors taking about 100ma at 13.6 Volts DC The lowest you can get away with given the fact that you want to bit bang ten of these. > rgds > ramana > > -- > 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 list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On 23 Aug 2000, at 17:17, Ramana wrote: > Hi, I need to control 10 DC motors using DC Voltage control. Can this be > done in Software PWM Only. Any Ideas. > Another point is that the motors will all be operated in 4 discrete > steps > off, low, medium, high. If this is so does it simplify things. > > What frequency of PWM would be good for DC Motor control The motors are > small motors taking about 100ma at 13.6 Volts DC > You will find numerous references on the PICLIST archive covering multiple PWM outputs in software under the "servo" keyword (including code listings). If the motor is a standard iron core (like most model railway motors) then I personally found 400Hz an excellent frequency, i.e. the motor started best at this frequency under heavy load. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________ -- 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

> Hi, I need to control 10 DC motors using DC Voltage control. Can this be > done in Software PWM Only. Any Ideas. I've done similar things a few times doing the PWM in software. There are different approaches to this, depending on how dedicated the processor is to just the PWM task. For example, a single dedicated PIC can do fast PWM by jumping an adjustable amount into a list of PWM "on" instructions, followed by a single PWM "off" instruction. One project I'm currently working on needs to control a DC motor and still do quite a bit of other stuff, like floating point servo computations. There I did the PWM from the interrupt routine. It's a tradeoff between how often you are willing to allow interrupts, how long a PWM period you can tolerate, and how much effective resolution you need. In this case I used a 20MHz PIC with a 500 Hz PWM frequency with the on time in steps of 50uS. This therefore required a regular interrupt every 50uS. We are still playing with how much granularity is really needed to drive the motor. I think we're overdoing it and could therefore decrease the PWM period, but others are investigating that right now. At 500Hz with this motor, you can hear the PWM frequency, but the inertia completely damps it out from a drive point of view. > Another point is that the motors will all be operated in 4 discrete > steps > off, low, medium, high. If this is so does it simplify things. Generally yes, since most software PWM schemes have a finite number of on/off slices per PWM interval. This means you only need 4 slices, which allows shorter periods. > What frequency of PWM would be good for DC Motor control The motors are > small motors taking about 100ma at 13.6 Volts DC You just have to experiment. The motor is a mechanical system that probably can't even "see" 100Hz. The whine at the PWM frequency may be more of a problem than any angular vibration. All things being equal, it's nice to do PWM for mechanical systems above the audible frequency range, but your not going to get that doing it in software. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, @spam@olinKILLspamcognivis.com, http://www.cognivis.com -- 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

On Wed, 23 Aug 2000, Ramana wrote: > Hi, I need to control 10 DC motors using DC Voltage control. Can this be > done in Software PWM Only. Any Ideas. > Another point is that the motors will all be operated in 4 discrete > steps > off, low, medium, high. If this is so does it simplify things. > > What frequency of PWM would be good for DC Motor control The motors are > small motors taking about 100ma at 13.6 Volts DC Well, how 'bout 8? http://www.dattalo.com/technical/software/pic/pwm8.asm Of course, you'll still need the low pass filter and power amplifier. Scott -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu