Analog signal conditioning
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Re: Analog signal conditioning
by John Ferrell-2
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Yes but that requires access at the tower top.
Also, I don't think the pot is a significant factor in the problem. Essentially I am trying to duplicate an ohm meter. It is interesting that MicroChip offers special purpose chips for Ohm meters. John Ferrell W8CCW "All that is necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke http://DixieNC.US ----- Original Message ----- From: "Michael Rigby-Jones" <Michael.Rigby-Jones@...> To: "Microcontroller discussion list - Public." <piclist@...> Sent: Wednesday, May 07, 2008 5:11 AM Subject: RE: [PIC]Analog signal conditioning > > >> -----Original Message----- >> From: piclist-bounces@... [mailto:piclist-bounces@...] On > Behalf >> Of John Ferrell >> Sent: 06 May 2008 20:31 >> To: Microcontroller discussion list - Public. >> Subject: Re: [PIC]Analog signal conditioning >> >> Until I fell into the trap I would have agreed with you. The AP Notes >> regarding ADC are serious reading. >> If you keep the pot onboard with the PIC you can get away with a lot. >> Reading the wiper of a 5K pot across Vcc and ground is not a problem. >> >> My Pot is at the end of about 75 feet of cable. The cable contributes > some >> unknown reactance in the configuration. The troublesome noise is a >> byproduct >> of the conversion within the PIC. The current requirements are likely > to >> be >> damaging to the Pot (500 ohms) if I simply put Vcc across it... I have > a >> 4.3K resistor in series with it. >> >> The conclusion that I draw at this time is that remote sensing is not > a >> simple matter even if it is just a resistor. >> > > Did you see my original post on differential measurement? > > 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. > ======================================================================= > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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RE: Analog signal conditioning
by Michael Rigby-Jones
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> -----Original Message----- > From: piclist-bounces@... [mailto:piclist-bounces@...] On Behalf > Of John Ferrell > Sent: 07 May 2008 13:30 > To: Microcontroller discussion list - Public. > Subject: Re: [PIC]Analog signal conditioning > > Yes but that requires access at the tower top. > Also, I don't think the pot is a significant factor in the problem. > I don't believe it would. You have a resistive sensor on the end of two long wires, so you can simply use a differential amp at the other end to remove (or at least attenuate) common mode noise. 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. ======================================================================= -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by M. Adam Davis-2
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Something you might try is measuring using current from the shack
side. Set up a constant current source (LM317 or similar) and then measure the voltage at the output of the regulator. The voltage will vary based on the position of the pot in order to make the current constant. It should help significantly, based on the description of the problems you're having. -Adam On 5/7/08, John Ferrell <johnferrell@...> wrote: > Yes but that requires access at the tower top. > Also, I don't think the pot is a significant factor in the problem. > > Essentially I am trying to duplicate an ohm meter. It is interesting that > MicroChip offers special purpose chips for Ohm meters. > > John Ferrell W8CCW > > "All that is necessary for the triumph of evil is for good men to do > nothing." -- Edmund Burke > http://DixieNC.US > > ----- Original Message ----- > From: "Michael Rigby-Jones" <Michael.Rigby-Jones@...> > To: "Microcontroller discussion list - Public." <piclist@...> > Sent: Wednesday, May 07, 2008 5:11 AM > Subject: RE: [PIC]Analog signal conditioning > > > > > > > >> -----Original Message----- > >> From: piclist-bounces@... [mailto:piclist-bounces@...] On > > Behalf > >> Of John Ferrell > >> Sent: 06 May 2008 20:31 > >> To: Microcontroller discussion list - Public. > >> Subject: Re: [PIC]Analog signal conditioning > >> > >> Until I fell into the trap I would have agreed with you. The AP Notes > >> regarding ADC are serious reading. > >> If you keep the pot onboard with the PIC you can get away with a lot. > >> Reading the wiper of a 5K pot across Vcc and ground is not a problem. > >> > >> My Pot is at the end of about 75 feet of cable. The cable contributes > > some > >> unknown reactance in the configuration. The troublesome noise is a > >> byproduct > >> of the conversion within the PIC. The current requirements are likely > > to > >> be > >> damaging to the Pot (500 ohms) if I simply put Vcc across it... I have > > a > >> 4.3K resistor in series with it. > >> > >> The conclusion that I draw at this time is that remote sensing is not > > a > >> simple matter even if it is just a resistor. > >> > > > > Did you see my original post on differential measurement? > > > > 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. > > ======================================================================= > > > > -- > > http://www.piclist.com PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- EARTH DAY 2008 Tuesday April 22 Save Money * Save Oil * Save Lives * Save the Planet http://www.driveslowly.org -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by Spehro Pefhany
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Quoting "M. Adam Davis" <stienman@...>:
> Something you might try is measuring using current from the shack > side. Set up a constant current source (LM317 or similar) and then > measure the voltage at the output of the regulator. The voltage will > vary based on the position of the pot in order to make the current > constant. > > It should help significantly, based on the description of the problems > you're having. > > -Adam Vdd +----------+ .-. | | 499R | | '-' | +------------+--------------------------------+----+ | | | \ | | .-. | - | 500R Pot | |<--+ BFTranzorb ^ \ | | | eg. 10V | | '-' | | | +---------+----------- | -------------------------------+ | | === | GND | | | | | | To ANx PIC .-. +------+---------------+ 2K | | | | + | | | --- '-' | --- 47uF/16V | | | +------+ | === GND The voltage at the ADC input is V = Rx/(499 + Rx) so it varies from 0 to about 2.5V for pot value from min to max (ignoring wire resistance etc.) It's a trivial exercise to solve for Rx as a function of ADC reading. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s...@... Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by John Ferrell-2
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Yes. If that 512 mv was stable my rotation measurement would be simple.
There are 360 degrees + an additional 90 degrees of overlap to report. John Ferrell W8CCW "All that is necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke http://DixieNC.US ----- Original Message ----- From: "Jinx" <joecolquitt@...> To: "Microcontroller discussion list - Public." <piclist@...> Sent: Wednesday, May 07, 2008 1:50 AM Subject: Re: [PIC]Analog signal conditioning >> The current requirements are likely to be damaging to the Pot >> (500 ohms) if I simply put Vcc across it > > Is that true ? 5000mV/500R -> 10mA -> 50mW > >> I have a 4.3K resistor in series with it > > That would reduce your measurable voltage range from 5000mV > to 521mV wouldn't it ? > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by John Ferrell-2
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I have tried that circuit without the "BFTranzorb" and the 2k resistor with
the same noisy results. I guess I live a sheltered life, this was the first time I had heard the word "Tranzorb" John Ferrell W8CCW "All that is necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke http://DixieNC.US ----- Original Message ----- From: "Spehro Pefhany" <speff@...> To: <piclist@...> Sent: Wednesday, May 07, 2008 11:58 AM Subject: Re: [PIC]Analog signal conditioning > Quoting "M. Adam Davis" <stienman@...>: > >> Something you might try is measuring using current from the shack >> side. Set up a constant current source (LM317 or similar) and then >> measure the voltage at the output of the regulator. The voltage will >> vary based on the position of the pot in order to make the current >> constant. >> >> It should help significantly, based on the description of the problems >> you're having. >> >> -Adam > > > > > Vdd > +----------+ > .-. > | | 499R > | | > '-' > | > +------------+--------------------------------+----+ > | | | > \ | | .-. | > - | 500R Pot | |<--+ > BFTranzorb ^ \ | | | > eg. 10V | | '-' > | | | > +---------+----------- | -------------------------------+ > | | > === | > GND | > | > | > | > | > | To ANx PIC > .-. +------+---------------+ > 2K | | | | + > | | | --- > '-' | --- 47uF/16V > | | | > +------+ | > === > GND > > > The voltage at the ADC input is > > V = Rx/(499 + Rx) so it varies from 0 to about 2.5V for pot value from > min to max (ignoring wire resistance etc.) > > It's a trivial exercise to solve for Rx as a function of ADC reading. > > Best regards, > Spehro Pefhany > -- > "it's the network..." "The Journey is the reward" > s...@... Info for manufacturers: > http://www.trexon.com > Embedded software/hardware/analog Info for designers: > http://www.speff.com > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by John Ferrell-2
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I will put this on my list of things to try.
John Ferrell W8CCW "All that is necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke http://DixieNC.US ----- Original Message ----- From: "M. Adam Davis" <stienman@...> To: "Microcontroller discussion list - Public." <piclist@...> Sent: Wednesday, May 07, 2008 10:54 AM Subject: Re: [PIC]Analog signal conditioning > Something you might try is measuring using current from the shack > side. Set up a constant current source (LM317 or similar) and then > measure the voltage at the output of the regulator. The voltage will > vary based on the position of the pot in order to make the current > constant. > > It should help significantly, based on the description of the problems > you're having. > > -Adam > > On 5/7/08, John Ferrell <johnferrell@...> wrote: >> Yes but that requires access at the tower top. >> Also, I don't think the pot is a significant factor in the problem. >> >> Essentially I am trying to duplicate an ohm meter. It is interesting that >> MicroChip offers special purpose chips for Ohm meters. >> >> John Ferrell W8CCW >> >> "All that is necessary for the triumph of evil is for good men to do >> nothing." -- Edmund Burke >> http://DixieNC.US >> >> ----- Original Message ----- >> From: "Michael Rigby-Jones" <Michael.Rigby-Jones@...> >> To: "Microcontroller discussion list - Public." <piclist@...> >> Sent: Wednesday, May 07, 2008 5:11 AM >> Subject: RE: [PIC]Analog signal conditioning >> >> >> > >> > >> >> -----Original Message----- >> >> From: piclist-bounces@... [mailto:piclist-bounces@...] On >> > Behalf >> >> Of John Ferrell >> >> Sent: 06 May 2008 20:31 >> >> To: Microcontroller discussion list - Public. >> >> Subject: Re: [PIC]Analog signal conditioning >> >> >> >> Until I fell into the trap I would have agreed with you. The AP Notes >> >> regarding ADC are serious reading. >> >> If you keep the pot onboard with the PIC you can get away with a lot. >> >> Reading the wiper of a 5K pot across Vcc and ground is not a problem. >> >> >> >> My Pot is at the end of about 75 feet of cable. The cable contributes >> > some >> >> unknown reactance in the configuration. The troublesome noise is a >> >> byproduct >> >> of the conversion within the PIC. The current requirements are likely >> > to >> >> be >> >> damaging to the Pot (500 ohms) if I simply put Vcc across it... I have >> > a >> >> 4.3K resistor in series with it. >> >> >> >> The conclusion that I draw at this time is that remote sensing is not >> > a >> >> simple matter even if it is just a resistor. >> >> >> > >> > Did you see my original post on differential measurement? >> > >> > 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. >> > ======================================================================= >> > >> > -- >> > http://www.piclist.com PIC/SX FAQ & list archive >> > View/change your membership options at >> > http://mailman.mit.edu/mailman/listinfo/piclist >> > >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > > -- > EARTH DAY 2008 > Tuesday April 22 > Save Money * Save Oil * Save Lives * Save the Planet > http://www.driveslowly.org > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by John Ferrell-2
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The conversion process in the AD is the source of the noise, the impedance
(not resistance) of the long wire run seems to be aggravating it. John Ferrell W8CCW "All that is necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke http://DixieNC.US ----- Original Message ----- From: "Michael Rigby-Jones" <Michael.Rigby-Jones@...> To: "Microcontroller discussion list - Public." <piclist@...> Sent: Wednesday, May 07, 2008 10:52 AM Subject: RE: [PIC]Analog signal conditioning > > >> -----Original Message----- >> From: piclist-bounces@... [mailto:piclist-bounces@...] On > Behalf >> Of John Ferrell >> Sent: 07 May 2008 13:30 >> To: Microcontroller discussion list - Public. >> Subject: Re: [PIC]Analog signal conditioning >> >> Yes but that requires access at the tower top. >> Also, I don't think the pot is a significant factor in the problem. >> > > I don't believe it would. You have a resistive sensor on the end of two > long wires, so you can simply use a differential amp at the other end to > remove (or at least attenuate) common mode noise. > > 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. > ======================================================================= > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by Spehro Pefhany
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Quoting John Ferrell <johnferrell@...>:
> I have tried that circuit without the "BFTranzorb" and the 2k resistor with > the same noisy results. *With* that value electrolytic capacitor mounted close to the MCU, and directly between analog ground and the analog input? > I guess I live a sheltered life, this was the first time I had heard the > word "Tranzorb" Perhaps better known by the generic term "TVS". The BF, of course, is "Big Fat". > John Ferrell W8CCW > > "All that is necessary for the triumph of evil is for good men to do > nothing." -- Edmund Burke > http://DixieNC.US > > ----- Original Message ----- > From: "Spehro Pefhany" <speff@...> > To: <piclist@...> > Sent: Wednesday, May 07, 2008 11:58 AM > Subject: Re: [PIC]Analog signal conditioning > > >> Quoting "M. Adam Davis" <stienman@...>: >> >>> Something you might try is measuring using current from the shack >>> side. Set up a constant current source (LM317 or similar) and then >>> measure the voltage at the output of the regulator. The voltage will >>> vary based on the position of the pot in order to make the current >>> constant. >>> >>> It should help significantly, based on the description of the problems >>> you're having. >>> >>> -Adam >> >> >> >> >> Vdd >> +----------+ >> .-. >> | | 499R >> | | >> '-' >> | >> +------------+--------------------------------+----+ >> | | | >> \ | | .-. | >> - | 500R Pot | |<--+ >> BFTranzorb ^ \ | | | >> eg. 10V | | '-' >> | | | >> +---------+----------- | -------------------------------+ >> | | >> === | >> GND | >> | >> | >> | >> | >> | To ANx PIC >> .-. +------+---------------+ >> 2K | | | | + >> | | | --- >> '-' | --- 47uF/16V >> | | | >> +------+ | >> === >> GND >> >> >> The voltage at the ADC input is >> >> V = Rx/(499 + Rx) so it varies from 0 to about 2.5V for pot value from >> min to max (ignoring wire resistance etc.) >> >> It's a trivial exercise to solve for Rx as a function of ADC reading. >> >> Best regards, >> Spehro Pefhany >> -- >> "it's the network..." "The Journey is the reward" >> s...@... Info for manufacturers: >> http://www.trexon.com >> Embedded software/hardware/analog Info for designers: >> http://www.speff.com >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s...@... Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by Jinx-4
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>Yes. If that 512 mv was stable my rotation measurement would
> be simple If the pot can have Vcc (I haven't met a pot that couldn't take 50mW), that would reduce the impedance and possibly make the noise disappear. Even something as simple as a capacitor on the ADC input may help Also improve resolution too, if that matters. Currently you'd be looking at about 1mV/degree over 450 degrees travel at the pot wiper With 5000mV reference, unamplified 521mV would mean about 5 degree resolution (ie 5000/1024 = 5mV per ADC bit) -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by John Ferrell-2
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This seems to be taking on a life of its own!
5 degrees is accurate enough for my needs. If I damage the sensor pot I am not sure I can repair or replace it. I have tried the capacitor but I am using a development board that does not make getting a cap directly on the AD pin easy. John Ferrell W8CCW "All that is necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke http://DixieNC.US ----- Original Message ----- From: "Jinx" <joecolquitt@...> To: "Microcontroller discussion list - Public." <piclist@...> Sent: Wednesday, May 07, 2008 7:03 PM Subject: Re: [PIC]Analog signal conditioning > >Yes. If that 512 mv was stable my rotation measurement would >> be simple > > If the pot can have Vcc (I haven't met a pot that couldn't take > 50mW), that would reduce the impedance and possibly make > the noise disappear. Even something as simple as a capacitor > on the ADC input may help > > Also improve resolution too, if that matters. Currently you'd be > looking at about 1mV/degree over 450 degrees travel at the > pot wiper > > With 5000mV reference, unamplified 521mV would mean about > 5 degree resolution (ie 5000/1024 = 5mV per ADC bit) > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by Jinx-4
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> This seems to be taking on a life of its own!
;-) Just exploring all the possibilities > If I damage the sensor pot I am not sure I can repair or replace it Well, that's fair enough. I'd be cautious too in that case -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by Apptech
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> This seems to be taking on a life of its own!
> 5 degrees is accurate enough for my needs. If time response is not critical, and it may be, then yuou can smooth this as much as you need to make it stable against any sensible amount of random noise. For faster response even a modest formally designed (as opposed to just a big RC) low pass filter (say 2 to 4 poles) will make a vast difference to the response time. A 4 pole LP filter can require as little as 2 transistors and some passives. You can get 3 with a single transistor if needs be. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Analog signal conditioning
by Jinx-4
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> The troublesome noise is a byproduct of the conversion within
> the PIC John, could you expand on or clarify that please. I'm unsure now whether the problem is with a pot at the end of a cable or down at the board -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
