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Chris
Guest
Tue Feb 09, 2010 10:54 pm
On Feb 9, 11:16 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
Quote:
On Tue, 9 Feb 2010 10:03:30 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
One of the guys in this thread sent me an Application Guide:
http://tinyurl.com/yd8yc5h
This is a very interesting read. However, the information here does
not seem to agree with the design suggestion for the crystal network
in the data sheet for the 6040B. Fig. 13 (http://tinyurl.com/yjyunkr
). Shows that Cxtal=C1+C2+Cstray. If I understand the application
guide 1/Cxtal=1/C1+1/C2.
Yes, but input (and stray capacitance should also be taken into
account).
If my crystal is rated 17pF, then by the
data sheet I need 2 8.5pF caps.
The data sheet is incorrect on this point.
Rs is current limiting. However, I
am using an off the shelf 3932160Hz crystal from Digi-Key, and there
is no indication to what the current limitation (per Rs in Fig. 13)
It's limited by the maximum crystal power dissipation and series
resistance of the crystal, crystal frequency, load capacitance, supply
voltage. HC-49 ~4MHz crystals are usually good for 1-2mW, some of the
SMD parts or kHz tuning fork types, down in the microwatts.
should be. Also, "Rc" is claimed to be to broaden the freq.
response. However, there is no reference to this in the application
guide.
Any guidance would be appreciated.
Thanks,
Chris Maness
KQ6UP
Given a physically larger crystal that can take 1-2mW of drive, you
can probably forget about Rs, use 22-27pF for the caps and 1M for the
parallel resistor. More caution is called for at high supply voltage.
Should I use 25pF trimmers so that I can dial in the freq.
Thanks,
Chris
Spehro Pefhany
Guest
Wed Feb 10, 2010 12:01 am
On Tue, 9 Feb 2010 14:04:39 -0800 (PST), Chris
<christopher.maness_at_gmail.com> wrote:
Quote:
On Feb 9, 1:23 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat
wrote:
On Tue, 9 Feb 2010 12:54:53 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
On Feb 9, 11:16 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat
wrote:
On Tue, 9 Feb 2010 10:03:30 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
One of the guys in this thread sent me an Application Guide:
http://tinyurl.com/yd8yc5h
This is a very interesting read. However, the information here does
not seem to agree with the design suggestion for the crystal network
in the data sheet for the 6040B. Fig. 13 (http://tinyurl.com/yjyunkr
). Shows that Cxtal=C1+C2+Cstray. If I understand the application
guide 1/Cxtal=1/C1+1/C2.
Yes, but input (and stray capacitance should also be taken into
account).
If my crystal is rated 17pF, then by the
data sheet I need 2 8.5pF caps.
The data sheet is incorrect on this point.
Rs is current limiting. However, I
am using an off the shelf 3932160Hz crystal from Digi-Key, and there
is no indication to what the current limitation (per Rs in Fig. 13)
It's limited by the maximum crystal power dissipation and series
resistance of the crystal, crystal frequency, load capacitance, supply
voltage. HC-49 ~4MHz crystals are usually good for 1-2mW, some of the
SMD parts or kHz tuning fork types, down in the microwatts.
should be. Also, "Rc" is claimed to be to broaden the freq.
response. However, there is no reference to this in the application
guide.
Any guidance would be appreciated.
Thanks,
Chris Maness
KQ6UP
Given a physically larger crystal that can take 1-2mW of drive, you
can probably forget about Rs, use 22-27pF for the caps and 1M for the
parallel resistor. More caution is called for at high supply voltage.
Should I use 25pF trimmers so that I can dial in the freq.
Thanks,
Chris
Your application cares about the last 0.01%?
Yes, my application does depend on the freq. being spot on. A little
off, and my film dialog will look like a bad kung foo flick.
It will always be a bit off, the engineering question is how much is
acceptable.
Quote:
You can't 'pull' a normal
quartz crystal much.
I am getting a freq. counter in a couple of days. It is supposed to
be good within .3Hz. I was thinking that with the trimmer, I could
account for a unknown, stray capacitance.
Just a thought. What do you think?
0.3Hz at what frequency? Accuracy or resolution? The first divided
output is divided by 16 (IIRC), so about 245kHz, so you ought to be
able to see +/-1ppm. Perhaps the slowest gate time is 3 seconds and
it's a conventional (rather than reciprocal) counter. But the counter
timebase might not be that *accurate*. ~4MHz crystals are typically
accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes,
just for comparison.
Quote:
Regards,
Chris
Chris
Guest
Wed Feb 10, 2010 12:04 am
On Feb 9, 1:23 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
Quote:
On Tue, 9 Feb 2010 12:54:53 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
On Feb 9, 11:16 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat
wrote:
On Tue, 9 Feb 2010 10:03:30 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
One of the guys in this thread sent me an Application Guide:
http://tinyurl.com/yd8yc5h
This is a very interesting read. However, the information here does
not seem to agree with the design suggestion for the crystal network
in the data sheet for the 6040B. Fig. 13 (http://tinyurl.com/yjyunkr
). Shows that Cxtal=C1+C2+Cstray. If I understand the application
guide 1/Cxtal=1/C1+1/C2.
Yes, but input (and stray capacitance should also be taken into
account).
If my crystal is rated 17pF, then by the
data sheet I need 2 8.5pF caps.
The data sheet is incorrect on this point.
Rs is current limiting. However, I
am using an off the shelf 3932160Hz crystal from Digi-Key, and there
is no indication to what the current limitation (per Rs in Fig. 13)
It's limited by the maximum crystal power dissipation and series
resistance of the crystal, crystal frequency, load capacitance, supply
voltage. HC-49 ~4MHz crystals are usually good for 1-2mW, some of the
SMD parts or kHz tuning fork types, down in the microwatts.
should be. Also, "Rc" is claimed to be to broaden the freq.
response. However, there is no reference to this in the application
guide.
Any guidance would be appreciated.
Thanks,
Chris Maness
KQ6UP
Given a physically larger crystal that can take 1-2mW of drive, you
can probably forget about Rs, use 22-27pF for the caps and 1M for the
parallel resistor. More caution is called for at high supply voltage.
Should I use 25pF trimmers so that I can dial in the freq.
Thanks,
Chris
Your application cares about the last 0.01%?
Yes, my application does depend on the freq. being spot on. A little
off, and my film dialog will look like a bad kung foo flick.
You can't 'pull' a normal
Quote:
quartz crystal much.
I am getting a freq. counter in a couple of days. It is supposed to
be good within .3Hz. I was thinking that with the trimmer, I could
account for a unknown, stray capacitance.
Just a thought. What do you think?
Regards,
Chris
MooseFET
Guest
Wed Feb 10, 2010 3:31 am
On Feb 9, 12:54 pm, Chris <christopher.man...@gmail.com> wrote:
Quote:
On Feb 9, 11:16 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat
wrote:
On Tue, 9 Feb 2010 10:03:30 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
One of the guys in this thread sent me an Application Guide:
http://tinyurl.com/yd8yc5h
This is a very interesting read. However, the information here does
not seem to agree with the design suggestion for the crystal network
in the data sheet for the 6040B. Fig. 13 (http://tinyurl.com/yjyunkr
). Shows that Cxtal=C1+C2+Cstray. If I understand the application
guide 1/Cxtal=1/C1+1/C2.
Yes, but input (and stray capacitance should also be taken into
account).
If my crystal is rated 17pF, then by the
data sheet I need 2 8.5pF caps.
The data sheet is incorrect on this point.
Rs is current limiting. However, I
am using an off the shelf 3932160Hz crystal from Digi-Key, and there
is no indication to what the current limitation (per Rs in Fig. 13)
It's limited by the maximum crystal power dissipation and series
resistance of the crystal, crystal frequency, load capacitance, supply
voltage. HC-49 ~4MHz crystals are usually good for 1-2mW, some of the
SMD parts or kHz tuning fork types, down in the microwatts.
should be. Also, "Rc" is claimed to be to broaden the freq.
response. However, there is no reference to this in the application
guide.
Any guidance would be appreciated.
Thanks,
Chris Maness
KQ6UP
Given a physically larger crystal that can take 1-2mW of drive, you
can probably forget about Rs, use 22-27pF for the caps and 1M for the
parallel resistor. More caution is called for at high supply voltage.
Should I use 25pF trimmers so that I can dial in the freq.
You may be better off placing a 100pF trimmer in series with the
crystal.
The C1 / C2 ratio doesn't want to be too far from 1.0 since it
controls the
swing at both ends.
The DC feedback resistor doesn't matter much so long as it is large
enough.
The crystal drive resistor needs to be low enough to get the crystal
to start
beyond that, you don't really use it to set the power level. The
capacitors
do more to set that than the resistor.
If you find that the oscillator runs slow, you may want to replace or
parallel
the crystal drive resistor with a small capacitor. This is not often
explained in
the data sheets and app notes but if the delay through the inverter of
the 4060 is
too large, the oscillator will want to run at a lower frequency. You
fix this by
adding a phase lead with the capacitor.
Quote:
Thanks,
Chris
Paul Keinanen
Guest
Wed Feb 10, 2010 8:44 am
On Tue, 09 Feb 2010 18:01:44 -0500, Spehro Pefhany
<speffSNIP_at_interlogDOTyou.knowwhat> wrote:
Quote:
But the counter
timebase might not be that *accurate*. ~4MHz crystals are typically
accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes,
just for comparison.
100 pm might apply to some cheap microprocessor crystals, but for
decades (before frequency synthesizers) , channel crystals were made
for radio telephones to within a few ppm. A 100 ppm crystal would have
caused the transmission on the wrong channel, a slightly smaller error
would cause bad audio distortion, since the signal would be partially
outside the receiver de modulator bandwidth.
When ordering a frequency for a specific frequency, specify also the
load capacitance or specify the frequency slightly (a few dozen ppm)
above the desired frequency and pull it down to the desired frequency
with a parallel capacitor. Pulling upwards is harder with a series
inductance.
Overtone crystals (typically above 20 MHz) have a more limited pulling
range.
Spehro Pefhany
Guest
Wed Feb 10, 2010 3:11 pm
On Wed, 10 Feb 2010 09:44:26 +0200, the renowned Paul Keinanen
<keinanen_at_sci.fi> wrote:
Quote:
On Tue, 09 Feb 2010 18:01:44 -0500, Spehro Pefhany
speffSNIP_at_interlogDOTyou.knowwhat> wrote:
But the counter
timebase might not be that *accurate*. ~4MHz crystals are typically
accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes,
just for comparison.
100 pm might apply to some cheap microprocessor crystals, but for
decades (before frequency synthesizers) , channel crystals were made
for radio telephones to within a few ppm. A 100 ppm crystal would have
caused the transmission on the wrong channel, a slightly smaller error
would cause bad audio distortion, since the signal would be partially
outside the receiver de modulator bandwidth.
When ordering a frequency for a specific frequency, specify also the
load capacitance or specify the frequency slightly (a few dozen ppm)
above the desired frequency and pull it down to the desired frequency
with a parallel capacitor. Pulling upwards is harder with a series
inductance.
Or if he really needs ppm-level accuracy/stability or better, replace
the crystal with a TCXO or VCTCXO (or even OCXO if warm-up time is not
important).
Eg.
http://www.ecsxtal.com/store/pdf/vc_txo_35sm.pdf
or
http://www.abracon.com/Precisiontiming/AOCJY.pdf
Specs are important, because the 4060 apparently won't work with
off-the-shelf frequencies, wheras the PIC or some equivalant
combination of HCMOS could.
Quote:
Overtone crystals (typically above 20 MHz) have a more limited pulling
range.
Related to the inverse of the square of the overtone, so 1/9 range for
a 3rd overtone.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff_at_interlog.com Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com
Spehro Pefhany
Guest
Wed Feb 10, 2010 5:49 pm
On Wed, 10 Feb 2010 07:52:52 -0800 (PST), Chris
<christopher.maness_at_gmail.com> wrote:
Quote:
On Feb 10, 6:11 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat
wrote:
On Wed, 10 Feb 2010 09:44:26 +0200, the renowned Paul Keinanen
keina...@sci.fi> wrote:
On Tue, 09 Feb 2010 18:01:44 -0500, Spehro Pefhany
speffS...@interlogDOTyou.knowwhat> wrote:
But the counter
timebase might not be that *accurate*. ~4MHz crystals are typically
accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes,
just for comparison.
100 pm might apply to some cheap microprocessor crystals, but for
decades (before frequency synthesizers) , channel crystals were made
for radio telephones to within a few ppm. A 100 ppm crystal would have
caused the transmission on the wrong channel, a slightly smaller error
would cause bad audio distortion, since the signal would be partially
outside the receiver de modulator bandwidth.
When ordering a frequency for a specific frequency, specify also the
load capacitance or specify the frequency slightly (a few dozen ppm)
above the desired frequency and pull it down to the desired frequency
with a parallel capacitor. Pulling upwards is harder with a series
inductance.
Or if he really needs ppm-level accuracy/stability or better, replace
the crystal with a TCXO or VCTCXO (or even OCXO if warm-up time is not
important).
Eg.http://www.ecsxtal.com/store/pdf/vc_txo_35sm.pdf
or http://www.abracon.com/Precisiontiming/AOCJY.pdf
Specs are important, because the 4060 apparently won't work with
off-the-shelf frequencies, wheras the PIC or some equivalant
combination of HCMOS could.
Overtone crystals (typically above 20 MHz) have a more limited pulling
range.
Related to the inverse of the square of the overtone, so 1/9 range for
a 3rd overtone.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers:http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
This is the actual crystal I ordered from digikey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=X975-ND
If I get the thing dialed in, the 30ppm is tolerable for my
application. I will try 25pF fixed capacitor for the PI network part
of the circuit. If I am paranoid should I still figure a value to
limit the current so that @ 12V the max power is ~2mw?
Yes, particularly if you care much about drift. This particular xtal
is rated at 1mW maximum.
Quote:
Am I running
into a greater chance that I will not be driving it enough to
oscillate?
Yes. You could empirically increase it until it doesn't start then go
down by a fairly large safety margin (maybe 3:1). Or work it out from
the transconductance of the oscillator amplifier (I think NXP
specifies typical values on their HC datasheet).
http://www.freescale.com/files/microcontrollers/doc/app_note/AN1783.pdf
Quote:
Or is the minimum power so far below the max power limit
that it does not matter? I will use a 2Meg resistor for the
foldback.
DC feedback = bias.
Quote:
Maybe a 25pF trimmer in parallel will let me dial the freq
right in. The specified crystal frequency is what I need. I am not
trying to shift it off the package frequency. I just want to put some
variability in so that I can compensate for stray capacitance after I
have mounted it in the tape deck.
Thanks Guys,
Chris Maness
Chris
Guest
Wed Feb 10, 2010 5:52 pm
On Feb 10, 6:11 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
Quote:
On Wed, 10 Feb 2010 09:44:26 +0200, the renowned Paul Keinanen
keina...@sci.fi> wrote:
On Tue, 09 Feb 2010 18:01:44 -0500, Spehro Pefhany
speffS...@interlogDOTyou.knowwhat> wrote:
But the counter
timebase might not be that *accurate*. ~4MHz crystals are typically
accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes,
just for comparison.
100 pm might apply to some cheap microprocessor crystals, but for
decades (before frequency synthesizers) , channel crystals were made
for radio telephones to within a few ppm. A 100 ppm crystal would have
caused the transmission on the wrong channel, a slightly smaller error
would cause bad audio distortion, since the signal would be partially
outside the receiver de modulator bandwidth.
When ordering a frequency for a specific frequency, specify also the
load capacitance or specify the frequency slightly (a few dozen ppm)
above the desired frequency and pull it down to the desired frequency
with a parallel capacitor. Pulling upwards is harder with a series
inductance.
Or if he really needs ppm-level accuracy/stability or better, replace
the crystal with a TCXO or VCTCXO (or even OCXO if warm-up time is not
important).
Eg.http://www.ecsxtal.com/store/pdf/vc_txo_35sm.pdf
or http://www.abracon.com/Precisiontiming/AOCJY.pdf
Specs are important, because the 4060 apparently won't work with
off-the-shelf frequencies, wheras the PIC or some equivalant
combination of HCMOS could.
Overtone crystals (typically above 20 MHz) have a more limited pulling
range.
Related to the inverse of the square of the overtone, so 1/9 range for
a 3rd overtone.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers:http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
This is the actual crystal I ordered from digikey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=X975-ND
If I get the thing dialed in, the 30ppm is tolerable for my
application. I will try 25pF fixed capacitor for the PI network part
of the circuit. If I am paranoid should I still figure a value to
limit the current so that @ 12V the max power is ~2mw? Am I running
into a greater chance that I will not be driving it enough to
oscillate? Or is the minimum power so far below the max power limit
that it does not matter? I will use a 2Meg resistor for the
foldback. Maybe a 25pF trimmer in parallel will let me dial the freq
right in. The specified crystal frequency is what I need. I am not
trying to shift it off the package frequency. I just want to put some
variability in so that I can compensate for stray capacitance after I
have mounted it in the tape deck.
Thanks Guys,
Chris Maness
John Fields
Guest
Wed Feb 10, 2010 8:41 pm
On Wed, 10 Feb 2010 07:52:52 -0800 (PST), Chris
<christopher.maness_at_gmail.com> wrote:
Quote:
---
In a Pierce oscillator, since the load capacitance is presented in
series with the crystal, if the crystal has a specified load capacitance
of 17pF the load capacitors should be about 35pF each.
---
Quote:
If I am paranoid should I still figure a value to
limit the current so that @ 12V the max power is ~2mw?
---
No, because in your case the crystal is designed to dissipate a
_maximum_ of one milliwatt. Also, you don't use the caps to change the
crystal's power dissipation, you change it by varying the value of the
series resistor.
---
Quote:
Am I running
into a greater chance that I will not be driving it enough to
oscillate? Or is the minimum power so far below the max power limit
that it does not matter?
---
Somewhere between the maximum rated power it'll dissipate when
oscillating and the minimum power required to get it to start is where
you should be working. Follow Spehro's advice.
---
Quote:
I will use a 2Meg resistor for the foldback.
---
It's not foldback, it's 'feedback' and it's used to bias the inverter
into its linear region so that noise will cause the crystal to start
ringing which will generate a voltage which will be fed into the
amplifier, amplified, and then sent back into the crystal to generate an
even larger voltage and...
---
Quote:
Maybe a 25pF trimmer in parallel will let me dial the freq
right in.
---
If it were me I'd use 33pF to ground on the input side of the inverter
and about a 70pF trimmer to ground on the other side so that it'd be
around the middle of its range at your operating frequency.
---
Quote:
The specified crystal frequency is what I need.
I am not trying to shift it off the package frequency.
I just want to put some variability in so that I can compensate
for stray capacitance after I have mounted it in the tape deck.
---
Then that's what loading it with the recommended load capacitance will
get you, since crystals are ground slightly high and the loading caps
are used to tune out strays an pull the crystal down to the desired
frequency.
Here are some other good reads:
http://www.ecsxtal.com/store/pdf/quar_des.pdf
http://www.ecsxtal.com/store/pdf/oscir_des.pdf
http://www.ecsxtal.com/store/pdf/clock_app.pdf
JF
Chris
Guest
Wed Feb 10, 2010 10:09 pm
On Feb 10, 8:49 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
Quote:
On Wed, 10 Feb 2010 07:52:52 -0800 (PST), Chris
christopher.man...@gmail.com> wrote:
On Feb 10, 6:11 am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat
wrote:
On Wed, 10 Feb 2010 09:44:26 +0200, the renowned Paul Keinanen
keina...@sci.fi> wrote:
On Tue, 09 Feb 2010 18:01:44 -0500, Spehro Pefhany
speffS...@interlogDOTyou.knowwhat> wrote:
But the counter
timebase might not be that *accurate*. ~4MHz crystals are typically
accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes,
just for comparison.
100 pm might apply to some cheap microprocessor crystals, but for
decades (before frequency synthesizers) , channel crystals were made
for radio telephones to within a few ppm. A 100 ppm crystal would have
caused the transmission on the wrong channel, a slightly smaller error
would cause bad audio distortion, since the signal would be partially
outside the receiver de modulator bandwidth.
When ordering a frequency for a specific frequency, specify also the
load capacitance or specify the frequency slightly (a few dozen ppm)
above the desired frequency and pull it down to the desired frequency
with a parallel capacitor. Pulling upwards is harder with a series
inductance.
Or if he really needs ppm-level accuracy/stability or better, replace
the crystal with a TCXO or VCTCXO (or even OCXO if warm-up time is not
important).
Eg.http://www.ecsxtal.com/store/pdf/vc_txo_35sm.pdf
or http://www.abracon.com/Precisiontiming/AOCJY.pdf
Specs are important, because the 4060 apparently won't work with
off-the-shelf frequencies, wheras the PIC or some equivalant
combination of HCMOS could.
Overtone crystals (typically above 20 MHz) have a more limited pulling
range.
Related to the inverse of the square of the overtone, so 1/9 range for
a 3rd overtone.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers:http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www..speff.com
This is the actual crystal I ordered from digikey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=X975-ND
If I get the thing dialed in, the 30ppm is tolerable for my
application. I will try 25pF fixed capacitor for the PI network part
of the circuit. If I am paranoid should I still figure a value to
limit the current so that @ 12V the max power is ~2mw?
Yes, particularly if you care much about drift. This particular xtal
is rated at 1mW maximum.
Am I running
into a greater chance that I will not be driving it enough to
oscillate?
Yes. You could empirically increase it until it doesn't start then go
down by a fairly large safety margin (maybe 3:1). Or work it out from
the transconductance of the oscillator amplifier (I think NXP
specifies typical values on their HC datasheet).
http://www.freescale.com/files/microcontrollers/doc/app_note/AN1783.pdf
Or is the minimum power so far below the max power limit
that it does not matter? I will use a 2Meg resistor for the
foldback.
DC feedback = bias.
Maybe a 25pF trimmer in parallel will let me dial the freq
right in. The specified crystal frequency is what I need. I am not
trying to shift it off the package frequency. I just want to put some
variability in so that I can compensate for stray capacitance after I
have mounted it in the tape deck.
Thanks Guys,
Chris Maness
Here is what I have so far. 2 Meg to bias. Two 20pF for the Pi
network. These have an equivalent of 10pF. I would imagine that any
stray capacitance would add to this in parallel. Hopefully the stray
capacitance is less than 7pF. That would satisfy the 17pF that the
crystal wants to see to be on freq. I will add a 20pF trimmer
parallel to the crystal for fine tuning. I would imagine I would need
to take any frequency measurements off of the next divider stage so as
not to introduce more stray capacitance and throw the freq.
measurement. As far as the current limiting resistor, I will use a
high value like a 20k pot with a 10k resistor in series. I will
decrease the value until the circuit starts oscillating. In the final
circuit I will use half that value.
Here is a photo of the circuit:
http://chrismaness.com/backend/spice_simulation/Photo_3.png
Thanks,
Chris Maness
Chris
Guest
Tue Feb 16, 2010 6:46 pm
I finished the this part of the project. The design with the 3.9Mhz
crystal with a CD4060 works perfectly. My tape deck is running
again. However, there is a small 480Hz hum in the record/play audio
now. This is very slight hum, not noticeable when there is dialog. I
did not notice this when the unit was running from a tuning fork time
reference. However, the tuning fork itself was audible outside the
chassis, and maybe masking my ability to hear the hum through the
headphones.
There is a voltage divider resistor (1k) in series with the circuit.
This was in place because the tuning fork ran off of 12V and the
supply was 24V. My circuit is using a voltage regulator to drop the
voltage down to 12V. There is now about a 8V drop across the
resistor. If I remove the resistor, the hum gets much louder. If I
shunt the power with a 1000uF cap after the resistor the hum gets
louder. If I shunt before the resistor the hum drops into the Nyquist
noise when I monitoring through the preamp. It is still there, but
buried. Is there a better way to get rid of this hum/ripple? The cap
is rather big and not as effective as I would like.
Thanks,
Chris Maness
Chris
Guest
Tue Feb 16, 2010 10:57 pm
On Feb 4, 7:00 pm, Ross Herbert <rherb...@bigpond.net.au> wrote:
Quote:
On Tue, 2 Feb 2010 08:29:47 -0800 (PST), Chris <christopher.man...@gmail.com
wrote:
:What is the simplest way to get480Hzfrom a crystal controlled
:oscillator? Looks like most of the pre-packaged XO's and VCXO, seem
:to put out much higher frequencies. Would a series of dividers be the
:best way?
:
:Thanks,
:Chris KQ6UP
You might be able to still pick up this surplus
itemhttp://surplussalespa..com/catalog/product_info.php?products_id=7474
With a bit of trimming I'm sure it could be pulled to 3.360kHz and then you can
use a divide by 7 counter using the HCF4018 to get480Hz.http://www.jaycar..com.au/images_uploaded/CD4018B.PDF
It is already built and installed. I just need to solve the little
hum problem that it created. However, overall it is working good.
Thanks,
Chris
ehsjr
Guest
Wed Feb 17, 2010 4:31 am
Chris wrote:
Quote:
I finished the this part of the project. The design with the 3.9Mhz
crystal with a CD4060 works perfectly. My tape deck is running
again. However, there is a small 480Hz hum in the record/play audio
now. This is very slight hum, not noticeable when there is dialog. I
did not notice this when the unit was running from a tuning fork time
reference. However, the tuning fork itself was audible outside the
chassis, and maybe masking my ability to hear the hum through the
headphones.
There is a voltage divider resistor (1k) in series with the circuit.
This was in place because the tuning fork ran off of 12V and the
supply was 24V. My circuit is using a voltage regulator to drop the
voltage down to 12V. There is now about a 8V drop across the
resistor. If I remove the resistor, the hum gets much louder. If I
shunt the power with a 1000uF cap after the resistor the hum gets
louder. If I shunt before the resistor the hum drops into the Nyquist
noise when I monitoring through the preamp. It is still there, but
buried. Is there a better way to get rid of this hum/ripple? The cap
is rather big and not as effective as I would like.
Thanks,
Chris Maness
Got a schematic of the power supply and the regulator?
Ed
Chris
Guest
Wed Feb 17, 2010 6:20 am
On Feb 16, 7:31 pm, ehsjr <eh...@nospamverizon.net> wrote:
Quote:
Chris wrote:
I finished the this part of the project. The design with the 3.9Mhz
crystal with a CD4060 works perfectly. My tape deck is running
again. However, there is a small 480Hz hum in the record/play audio
now. This is very slight hum, not noticeable when there is dialog. I
did not notice this when the unit was running from a tuning fork time
reference. However, the tuning fork itself was audible outside the
chassis, and maybe masking my ability to hear the hum through the
headphones.
There is a voltage divider resistor (1k) in series with the circuit.
This was in place because the tuning fork ran off of 12V and the
supply was 24V. My circuit is using a voltage regulator to drop the
voltage down to 12V. There is now about a 8V drop across the
resistor. If I remove the resistor, the hum gets much louder. If I
shunt the power with a 1000uF cap after the resistor the hum gets
louder. If I shunt before the resistor the hum drops into the Nyquist
noise when I monitoring through the preamp. It is still there, but
buried. Is there a better way to get rid of this hum/ripple? The cap
is rather big and not as effective as I would like.
Thanks,
ChrisManess
Got a schematic of the power supply and the regulator?
Ed
Yes I will post them shortly. The unit runs off of two separate
battery packs. 1 24V pack with a negative ground, and one 12V pack
with a positive ground. The schematics I have are separate because I
was modeling them in LTSpice.
Chris
RFI-EMI-GUY
Guest
Thu Feb 18, 2010 5:08 am
On 2/16/2010 11:46 AM, Chris wrote:
Quote:
I finished the this part of the project. The design with the 3.9Mhz
crystal with a CD4060 works perfectly. My tape deck is running
again. However, there is a small 480Hz hum in the record/play audio
now. This is very slight hum, not noticeable when there is dialog. I
did not notice this when the unit was running from a tuning fork time
reference. However, the tuning fork itself was audible outside the
chassis, and maybe masking my ability to hear the hum through the
headphones.
There is a voltage divider resistor (1k) in series with the circuit.
This was in place because the tuning fork ran off of 12V and the
supply was 24V. My circuit is using a voltage regulator to drop the
voltage down to 12V. There is now about a 8V drop across the
resistor. If I remove the resistor, the hum gets much louder. If I
shunt the power with a 1000uF cap after the resistor the hum gets
louder. If I shunt before the resistor the hum drops into the Nyquist
noise when I monitoring through the preamp. It is still there, but
buried. Is there a better way to get rid of this hum/ripple? The cap
is rather big and not as effective as I would like.
Thanks,
Chris Maness
Problem could be that when using a tuning fork oscillator, the signal
was a sine wave. Now dealing with digital divider you have a square wave
and what you are hearing are harmonics. Look up 'super filters' these
are capacitor/pass transistor arrangement to effectively increase
capacitance through gain of the transistor.
--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©
"Use only Genuine Interocitor Parts" Tom Servo ;-P
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