13 May 17:09
Re: [PIC] CCP1 Glitches in noisy environment (RC Tx)
From: Gordon Williams <g_will <at> cyberus.ca>
Subject: Re: [PIC] CCP1 Glitches in noisy environment (RC Tx)
Newsgroups: gmane.comp.hardware.microcontrollers.pic
Date: 2008-05-13 15:09:39 GMT
Subject: Re: [PIC] CCP1 Glitches in noisy environment (RC Tx)
Newsgroups: gmane.comp.hardware.microcontrollers.pic
Date: 2008-05-13 15:09:39 GMT
Here are some readings across the battery just after the battery connector. The battery is NiCad. I've taken the spring hook clip off of the probe end. The ground lead is about 20 cm long. The scope that I am using is a Bitscope. The probe and scope front end are good to 100 MHz bandwidth. The sample rate is 25 Mhz. If I attach the ground lead to the negative battery terminal but leave the probe free I get 20 mV of noise. If I touch the probe to the ground lead connection I get 60 mV of noise (should be short circuit). Leaving the gnd lead attached and I put the probe on REF. I get 20 mV of noise. Taking the lead off and leaving it on ref there is < 5 mV of noise. This is using the 1x probe and 130mv range. Across the battery For different settings I get different readings: 10x probe, AC +/-Range Noise Vp-p 1.3V 0.69 6.0 0.94 12.0 1.6 1x probe, AC 130 mV 0.06 noise 600 mV 0.08 1.2 V 0.13 3.16 0.15 As you can see, they aren't consistent. Both 1x and 10x noise appears to increase with range setting. Both essentially double from the lowest to the highest in the range. The noise on the 10x probe setting is 10 times the 1x setting. Which one should I believe? Should I be using only the 1x probe setting? I assume that the amount of roll-off I have changes with the settings. The noise is at 72 MHz so it is getting close to the 100 MHz. I don't know what you mean when you say "When you are measuring noise, you must move your ground probe terminal near the probe active ground terminal as well." The transmitter that I am modifying is a hitec laser 4. Guessing that they make 1000s per year. PCB is single sided, no shielding, no separate grounds, looks like there are at least 3 ground loops... You can see pics and the schematic on the FCC site: https://gullfoss2.fcc.gov/oetcf/eas/reports/ViewExhibitReport.cfm?mode=Exhibits&RequestTimeout=500&calledFromFrame=N&application_id=100973&fcc_id='IFHLAS46' I'm replacing IC1 with a PIC on a daughter board and then making the connections that I need at the location of IC1. Interesting that you don't think that it is noise. What else could it be? Regards, Gordon Williams ----- Original Message ----- From: "Vasile Surducan" <piclist9 <at> gmail.com> To: "Microcontroller discussion list - Public." <piclist <at> mit.edu> Sent: Tuesday, May 13, 2008 12:31 AM Subject: Re: [PIC] CCP1 Glitches in noisy environment (RC Tx) : On 5/12/08, Gordon Williams <g_will <at> cyberus.ca> wrote: : > Richard and David, : > : > The stack is OK. : > : > The noise appears to be coming in on the 5v supply and/or ground line(s) : > from the main board. There is no separate ground for the analog, digital : > and RF sections. They are all lumped together. The RF runs directly off of : > the battery voltage, 9.6 volts nom. At the battery with the scope I have : > about 2 volts p-p of noise. : > : > I put a 1 ohm resistor in the supply line expecting that it would make an RC : > filter with the caps on the daughter board because the noise is 72 Mhz. It : > improved things slightly - maybe. : > : > After doing a bit of research, it looks like the 10uF Tant won't do much for : > noise at this frequency because of the ESR. The three 0.1uF ceramics should : > do OK. : > : > I have some ferrite beads on hand that I would like to try out. They are : > axial single beads BL01RN1 : > http://www.electrokit.se/download/0900766b80098a6d.pdf : > : > Putting one on the tip of the scope probe and then measuring the noise : > across the battery terminals dropped the noise by 1/2. : : What scope do you have and how are your probes (1:1, 1:10?) : 0.9Vpp noise directly on battery terminals is very weird. : I think you have a ground problem there or measuring problems or toy : scope or all of them. When you are measuring noise, you must move your : ground probe terminal near the probe active ground terminal as well. : A 72Mhz RF module can't give you such a noise only if its homebrewed : and incorrect shielded. Suply the RF through an 300ohm at 100Mhz : ferrite bead and all SPI or I2C signals through 60-100ohm/100MHz : ferrite beads. I presume RF transmitter is proffesional and well : designed, else this is a medicine for a wooden leg. : : Anyway, my impression is not the noise the problem which is causing : PWM's glitches... : I've seen it on my projects too where it was less than 100mV noise, : but it wasn't in compare mode. : : Wesley : : : > : > Should I be putting a ferrite bead on both the supply and ground line to the : > daughter board? : > : > Would it be a good idea to add a 1uf ceramic as well? : > : > Thanks for your ideas - this is well beyond me. : > : > Regards, : > : > Gordon Williams : > : > : > ----- Original Message ----- : > From: "Richard Prosser" <rhprosser <at> gmail.com> : > To: "Microcontroller discussion list - Public." <piclist <at> mit.edu> : > Sent: Monday, May 12, 2008 3:50 PM : > Subject: Re: [PIC] CCP1 Glitches in noisy environment (RC Tx) : > : > : > : Gordon, : > : You're not just running out of stack or something like that are you? : > : Have you checked stack usage? : > : : > : Otherwise, could the RF be getting back into the chip via an : > : unprotected pin. Do you have ferrite beads / caps on all input (& : > : possibly output ?) pins if the RF level is so high? Once the : > : protection diodes start conducting all sorts of strange things can : > : happen. : > : : > : RP : > : : > : 2008/5/13 Gordon Williams <g_will <at> cyberus.ca>: : > : > : > : > : > : > : You have a huge noise there, try to see why. Almost 2Vpp of noise is a : > : > : > : real mess. : > : > : It's possible that sometime the PWM dutycycle be longer that PWM : > period? : > : > : Only then the CCP output remains high. Maybe a compiler problem ? : > : > : > : > I should have been clearer about the part of the CCP module that I was : > : > using. I'm using the "compare" rather than the "pwm" part. : > : > : > : > I don't think that it is a compiler problem as the effect is random and : > : > nothing else appears to be affected. I can't see it just jumping off : > : > somewhere else in the program and not having an effect on either the : > Timer 1 : > : > or the CCPR1 register. : > : > : > : > I need to look more carefully at the noise on the 5 V section of the : > : > daugther board. It is buried in the transmitter box and a PIA to get : > at. : > : > Because the ADCs are noise free, my assumption was that it was fairly : > noise : > : > free. : > : > : > : > How much noise on the power lines is acceptable? : > : > : > : > If the noisy supply voltage stays between 2.0 and 5.5 volts, is that OK? : > Or : > : > does the noise component need to be kept below some value p-p? : > : > : > : > Regards, : > : > : > : > Gordon Williams : > : > : > : > : > : > : On 5/12/08, Gordon Williams <g_will <at> cyberus.ca> wrote: : > : > : > Hi All, : > : > : > : > : > : > I'm having problems tracking down the reason of some glitches : > occurring : > : > on : > : > : > the CCP1 output and it is driving me a bit crazy. : > : > : > : > : > : > I'm putting some smarts into a basic RC transmitter. I've replaced : > the : > : > : > current chip producing the pulse train to the RF section with a : > daughter : > : > : > board and added a cell phone LCD, some switches and Serial port for : > : > input : > : > : > and output. The serial port and LCD (spi) work fine and they don't : > have : > : > any : > : > : > glitches. The 5 ADC readings for the joysticks (4) and battery : > voltage : > : > also : > : > : > work well with only 1 bit of noise on a 10 bit reading (referenced : > to : > : > the : > : > : > power and gnd lines). : > : > : > : > : > : > The PIC that I am using is the 16F886. Its supply is a 78L05 on the : > : > main : > : > : > board and I have a 10uf Tant and three 0.1uF on the power lines on : > the : > : > : > daughter board. The daughter board is single sided with a ground : > plane : > : > pour : > : > : > under the PIC and every else where I could. Because I don't have : > ADC : > : > : > problems or serial or spi errors that noise must be reasonably : > : > constrained, : > : > : > I think. : > : > : > : > : > : > I'm using CCP1 (pin C2) to produce the PPM that goes to the RF : > section. : > : > It : > : > : > is the standard PPM protocol (each channel pulse is 1 to 2 ms wide : > : > including : > : > : > the following 0.3 ms pulse, repeated every 20ms). : > : > : > : > : > : > Timer1 runs freely. With a CCP1 interrupt (my only interrupt) I : > update : > : > : > CCPR1 with the duration until the next transition high or low and : > the : > : > : > CCP1CON bits to set the next transition in the correct direction. : > My : > : > main : > : > : > program clears a flag and that is all. : > : > : > : > : > : > Most of the time it works perfectly and looks like: : > : > : > http://www.cyberus.ca/~g_will/TxGlitch/NoGlitch1.jpg : > : > : > : > : > : > or detail : > : > : > : > : > : > http://www.cyberus.ca/~g_will/TxGlitch/NoGlitch.jpg : > : > : > : > : > : > The receiver pulses for the first 4 channes are shown in the logic : > : > section : > : > : > below. : > : > : > : > : > : > Every 20 to 100 frames on average (sometimes they are consectutive : > : > frames) I : > : > : > get a glitch: : > : > : > : > : > : > http://www.cyberus.ca/~g_will/TxGlitch/Glitch1.jpg : > : > : > : > : > : > or : > : > : > : > : > : > http://www.cyberus.ca/~g_will/TxGlitch/Glitch2.jpg : > : > : > : > : > : > The green lines indicate where the signal should have been. : > : > : > : > : > : > There is a fair bit of noise - about 1.8 volts p-p because the scope : > : > ground : > : > : > was attached to the battery neg lead. I don't think that my probes : > are : > : > very : > : > : > well shielded either. The noise is from the 72 Mhz RF. : > : > : > : > : > : > In each case the low output flips high. My question is WHY? : > : > : > : > : > : > Timer 1 keeps on rolling as there is no problem with frame spacing : > or : > : > the : > : > : > width or placement of the next good pulse. : > : > : > : > : > : > CCPR1 is not upset or incorrectly set for the same reasons - because : > the : > : > : > next good pulse is in the proper location relative to the last good : > : > pulse. : > : > : > : > : > : > The serial and LCD have been comment out. I'm reading 2 ADC on port : > A : > : > and : > : > : > 3ADC on port B. All other pins on ports A,B,C are inputs and some : > are : > : > : > floating (could this be a problem?) : > : > : > : > : > : > Is there anything else on the chip that may be miss-configured that : > may : > : > be : > : > : > giving me a problem? : > : > : > : > : > : > The chip docs say: : > : > : > Note: Clearing the CCP1CON register will force : > : > : > the CCPx compare output latch to the : > : > : > default low level. This is not the PORT I/O : > : > : > data latch. : > : > : > : > : > : > But I don't think that this applies to me. The only time that I do : > : > anything : > : > : > with the CCP1CON is during the long bit in the frame between the : > pulse : > : > : > series and the glitch doesn't always happen there. : > : > : > : > : > : > It is not read-mod-write ... I'm not writing anything to the port. : > : > : > : > : > : > I read the errata - nothing there indicated a problem. : > : > : > : > : > : > Any ideas what I should be looking at/ trying next?? : > : > : > : > : > : > - I guess I should look at the 5 v power going to the chip to see : > that : > : > it is : > : > : > truly quiet and doesn't have a spike. Brown out is disabled. : > : > : > : > : > : > - Should set the un-used outputs to either high or low. - Good : > right? : > : > : > : > : > : > Funny that it is only affecting one pin that I can see. : > : > : > : > : > : > Looking for suggestions... : > : > : > : > : > : > Regards, : > : > : > : > : > : > Gordon Williams : > : > : > : > : > : > -- : > : > : > 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 : > : > : : > : > : > : > -- : > : > 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 : > : : > : > -- : > 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 : -- -- 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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