Re: CCP1 Glitches in noisy environment (RC Tx)

> 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.
>
> 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@...>
> To: "Microcontroller discussion list - Public." <piclist@...>
> 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@...>:
> : >
> : >
> : > : 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@...> 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