Author Topic: GPSDO: PLL or MCU controlled?  (Read 10803 times)

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Offline Theboel

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Re: GPSDO: PLL or MCU controlled?
« Reply #25 on: August 03, 2019, 12:33:12 pm »
Hi All,

Could I suggest something ?

1. You need to think very serious about how to check Your GPSDO design, if You want You can use TAPR TIC for measurement.
https://tapr.org/kits_ticc.html
This is not a toy believe me only very few "thing" has same capabilities or better than this board but with Thousand USD price tag.
but if You like adventure You can try this :
https://www.ebay.co.uk/itm/FA1-USB-simple-High-Precision-Virtual-Frequency-Counter-Frequency-Analyzer/173883937521?hash=item287c4a52f1:g:hoMAAOSwEbxcwZQ4
or this
https://www.ebay.co.uk/itm/FSA3011-OCXO-GPSDO-Atom-Clock-Frequency-stability-Analyzer/254258571356?hash=item3b32fde85c:g:6bUAAOSw7CBc~PXi


2. GPSDO for me has 3 ingredient :
a. Oscillator You want to discipline, almost anything You can discipline. OCXO,TCXO, Rb, even active Hidrogen maser
b. GPS module use to generate clock use for discipline the oscillator, You can use any GPS module with 1PPS out from "fake ublox up to very high price geodetic GPS receiver"
c. Control unit, You can Go to TIC+MCU, etc

3. If You want to just have GPSDO with average performance I think nothing simpler than JRmiller design
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm
but if You want or can more bell and whistle You can try Lars design
https://www.eevblog.com/forum/projects/lars-diy-gpsdo-with-arduino-and-1ns-resolution-tic/
in case You want MCU without to many complicated You can look at leo bodnar design
https://www.eevblog.com/forum/metrology/leo-bodnar-mini-precision-gps-reference-clock-teardown/msg1398826/#msg1398826

if You ask me I will use MCU with TIC like lars design with some additional sauce    ;) ;) ;)
 
« Last Edit: August 03, 2019, 12:51:27 pm by Theboel »
 

Offline fourfathom

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Re: GPSDO: PLL or MCU controlled?
« Reply #26 on: August 03, 2019, 08:09:51 pm »
One quick note: For the interpolating part highly deterministic delay is needed that is for that part CPLD is a must and FPGA won't cut (not only that, CPLDs with FPGA like internal architecture won't cut either).
What kind of specs are you looking for here?  I'm surprised that you can't get these deterministic delays with a CPLD, since 100MHz (and faster) internal clocking is pretty typical and with clocked outputs the delay variation will be within a couple of nanoseconds.
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Offline Johnny B Good

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Re: GPSDO: PLL or MCU controlled?
« Reply #27 on: August 04, 2019, 01:47:09 pm »
I've just placed an order for 50x SOP8OP8 TSSOP8 SMD To DIP8 Adapter 0.65/1.27mm PCB Board F6T4 as a result of checking out ebay for those LEA-6Ts. At just £1.06 delivered, it was a bargain I just couldn't resist,

Same here, same price! Couldn't resist that.

More importantly, the seller in France that I got my NEO-M8T from has more:

https://www.ebay.co.uk/itm/Ublox-NEO-M8T-0-IC-GNSS-Receiver-GPS-GLONASS-BeiDou-Galileo/193014081445?hash=item2cf08927a5:g:3YoAAOSwt91cxbn8

As far as I can tell, these are the genuine article. Mine are working well and I flashed them with the latest firmware.

The main differences between the NEO and LEA are the NEO does not have an internal bias-t for antenna power, but instead has a second internal LNA and a filtered power output for feeding into an external bias-t. That's what I did. I designed a simple development circuit and had the PCBs made at JLC - I still have a couple spare...


 Unfortunately, I'm only at the veroboard and pre-assembled RasPi / Arduino GPS module level of construction (I've no plans to solder bare u-Blox modules onto custom boards right now). Mind you, until I took a look at u-blox's data sheet on the 8T series to check the pin count, I'd briefly entertained the notion of replacing the M8N chip (24 pin) on the original module board that had suffered a jolt of 12 volt up its backside (the now destroyed PPS pin) with an 8T until I'd seen the pin out count mismatch (28 pins).

 As much as I hate dealing with anyone shipping via Hong Kong these days, I just might go for one of those drone navigation modules after all if I still can't track down a reasonably priced less long distance source over the next few months.

 At least the pin count was correct on the modules soldered to the navigation module's pcb in the more revealing pictures in the link I'd posted and I do know how to extract the ceramic patch antenna to solder an SMA antenna socket pigtail to the board and where to access the PPS and the serial port connections to pervert one of them into doing duty as master to the OCXO in my current project's box of tricks. As I mentioned in another thread, "There's more than one way to skin a cat." :)

 For some reason, I'd been reminded about those cheap chinese Hakko T12 soldering station clones (from a posting in the FY6600 thread way back in November last year - where else? ::)) and had finally taken the hint to look more deeply into the subject of modern soldering station technology, in particular of the (what else? - I own an Fy6600 for goodness' sake!) cheap kind.

 So, now I'm in the market for help and advice on the matter of soldering station technology and since you're working on smd circuit boards, I thought you might have some useful advice to offer in this matter, if I might be so cheeky as to prevail upon your kindness (even if it's just a link to a blog or discussion thread to save you the tedium of repeating what almost everyone else would have to say on the subject  ::) ).

 I'd already come across a video tutorial on the business of building a Hakko T12 clone station from a kit of parts but it's obviously a year or more older (I couldn't date the tutorial but most of the links to sources of supply are 'dead' with redirects to possible alternatives).

 The first link redirected me to a selection of everything needed except the 24 volt 4 amp psu in the suggested parts list, leaving me the impression that there are many ways I can take a wrong turn in my quest to build a Hakko T12 clone setup on the cheap, hence my taking this opportunity to seek your advice on this aspect of the hobby of diy electronics project work.

 My modest collection of 15, 20 and 24 watt Antex soldering irons just aren't going to cut it with my more recent interest in electronic projects hence my "sudden" interest in modern soldering technology that's now seemingly within the financial grasp of the home hobbyist market.

 I realise it's a bit of an imposition to spring such a "left field" question 'out of the blue' on you like this but I figure the worst that could happen is to be told to take a hike and do my own 'homework', so worth the tiny risk of being sent off with a flea in my ear in putting that adage of "Ask, and it shall be told" to the test. :)

 BTW, getting back on topic, I've managed to open the holes up required to fit a barrel jack onto the back edge of the veroboard in my GPSDO. I haven't got as far as soldering anything onto the veroboard just yet; there are still a few details to be sorted out before then.

 Still, I have cut a few tracks to match where I've placed the major components as shown in the attached images, so at least part of the final layout is now decided (if not quite set in stone - veroboard being veroboard, there's still opportunity to make last minute changes if deemed essential).

JBG

John
 

Offline Vgkid

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Re: GPSDO: PLL or MCU controlled?
« Reply #28 on: August 04, 2019, 02:07:16 pm »
Look into csgshop.com they sell a ton of ublox modules. I wish shipping was cheaper to usa. Keeps me from buying stuff.
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Offline Johnny B Good

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Re: GPSDO: PLL or MCU controlled?
« Reply #29 on: August 04, 2019, 04:39:21 pm »
Look into csgshop.com they sell a ton of ublox modules. I wish shipping was cheaper to usa. Keeps me from buying stuff.

 I presume you were trying to remind of the exorbitant pricing of u-blox product in the USA and how lucky I am to be able to find Chinese bargains?  :-//

JBG
John
 

Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #30 on: August 04, 2019, 08:54:11 pm »
I realise it's a bit of an imposition to spring such a "left field" question 'out of the blue' on you like this...

Not at all, it's all good. Not that I can be of much help with the matter unfortunately.

One of the few decent investments I made some years ago was a Weller soldering station (the basic analogue temperature control one) and a couple of irons; a WSP80 for general soldering and a WMP65 micro pencil for the fine pitch stuff. I might make a different choice now, but at the time there wasn't as much choice and the Weller does the job perfectly well. It just takes up a bit too much of my very limited desk space.

The bigger WSP80 gets far more use, especially now I've discovered drag soldering. A bit late to the party perhaps, but I'm glad I got there. I persevered for ages with a 0.1mm tip on the micro pencil, soldering 0.5mm pitch ICs a pin at a time under the microscope.

The one bit of advice I would give, given that most interesting things now are SMD, is to get an iron that you can buy a gull wing tip for. They go by other names too and have a concave dish in the tip which holds a tiny blob of solder. I watched a few videos on drag soldering, then gave it a go on some 28 pin TSSOPs. The videos made it look ridiculously easy, and to my amazement it actually was. The flux was critical; I got a bottle of RA flux from Farnell along with the tip. It works much better than my flux pen for this purpose:

https://uk.farnell.com/mg-chemicals/835-100ml/rosin-soldering-flux-bottle-125ml/dp/2903909

I must admit that ublox module was a pain to solder. Making the rest of the board went like a charm (even the 0603 parts that were small enough to carelessly inhale) but that module just sucked the heat right out of the iron before it could make a joint. By the end of it I had turned up the heat to about 330C, iirc, with the WSP80 and was just managing to get good joints made without feeling I was going to overcook it or leave a cold joint. That was before I got that bottle of good flux though, which I think would have made quite a difference in getting the copper to wet. Still, it survived.

Should you change your mind about giving it a go, give me a shout about those spare PCBs.

I've not had chance to do anything with the GPSDO today, other than plot and scheme. As much as I like the (relative) simplicity of a PLL, my original idea was to use an MCU controller. I need one for sync'ing my derived PPS anyway. Using basic frequency locking control of the OCXO on an MCU though isn't conducive to keeping that DPPS where it should be. It drifts, slowly but surely.

It's much easier to use phase locking on the OCXO than to try to keep the DPPS sync'd without it. So... I'm considering doing the phase locking in the MCU, either with a capacitor and ADC or one of those TI chips mentioned earlier in the thread... implementing what I now know is known as a TIC. Along with learning how to use the dsPIC for actual digital signal processing. I could even try pressing the CTMU (essentially a built-in TIC) on the dsPIC to the task, but it seems so unstable I don't know if it's worth the effort.

...and then I wonder if it's all worth the extra effort when I can already get the OCXO more accurate and stable than I'll likely ever need. But that's not the point, I guess.

It's good to have choices  :-DD
« Last Edit: August 04, 2019, 08:57:57 pm by Illusionist »
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Offline Theboel

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Re: GPSDO: PLL or MCU controlled?
« Reply #31 on: August 05, 2019, 12:22:15 am »
 Hi illusionist,
Good choice for TIC+MCU.
In lars thread there is a paper about what he has done and reason why he done it it's very worthy to read.
Especially about temperature control. If You put the whole GPSDO in a thermal isolated box and use his temp control You will have DOCXO and your also You can keep everything in stable environment.
If You like maybe You can also add more thing like kalman filter, sawtooth correction to Your GPSDO
 
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Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #32 on: August 05, 2019, 01:39:34 am »
Theboel, yes, I've been reading about Kalman filtering. Trying to understand it, and how to implement it.

I do think that phase locking is the best way for what I'm trying to achieve and it would be fun (if a steep learning curve for me) to implement it in a MCU. While my current design works quite well, I like the further challenge.

I've glanced over Lars' design but don't want to read it in depth because I really want to figure it out myself. I'm trying to balance reading and learning enough to do it, and discovering others' ideas that might be helpful, without just duplicating their work.

As a hobbyist, all of this is just for fun and a learning exercise. It also lets me indulge my obsession for accuracy and precision.
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Offline edigi

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Re: GPSDO: PLL or MCU controlled?
« Reply #33 on: August 05, 2019, 10:57:12 am »
What kind of specs are you looking for here?  I'm surprised that you can't get these deterministic delays with a CPLD, since 100MHz (and faster) internal clocking is pretty typical and with clocked outputs the delay variation will be within a couple of nanoseconds.

What I actually wrote that with CPLD you do get more deterministic delay than with FPGA (unless CPLD is internally uses an FPGA like architecture). No other clock is involved in my solution than the 10 MHz (the reference that is GPS disciplined) and the GPS pulse output.

Sure, that the biggest noise contributing factor is the jitter from the GPS pulse output (https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_%28GPS.G6-X-11007%29.pdf), however it costs close to nothing to practically entirely eliminate the uncertainty of the GPS pulse period measurement in reference periods terms (approx. 4 EUR for the TDC chip, 5 passive components and some board space; I've actually reused everything from my principally similar frequency counter including the proto PCB made by JLC).
Practically eliminate means 100 picoseconds range that is so minuscule compared to the jitter from the GPS pulse output that one can entirely focus on that (getting rid of the added variance of the GPS pulse output).
 

Offline Theboel

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Re: GPSDO: PLL or MCU controlled?
« Reply #34 on: August 05, 2019, 01:22:19 pm »
What kind of specs are you looking for here?  I'm surprised that you can't get these deterministic delays with a CPLD, since 100MHz (and faster) internal clocking is pretty typical and with clocked outputs the delay variation will be within a couple of nanoseconds.

What I actually wrote that with CPLD you do get more deterministic delay than with FPGA (unless CPLD is internally uses an FPGA like architecture). No other clock is involved in my solution than the 10 MHz (the reference that is GPS disciplined) and the GPS pulse output.

Sure, that the biggest noise contributing factor is the jitter from the GPS pulse output (https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_%28GPS.G6-X-11007%29.pdf), however it costs close to nothing to practically entirely eliminate the uncertainty of the GPS pulse period measurement in reference periods terms (approx. 4 EUR for the TDC chip, 5 passive components and some board space; I've actually reused everything from my principally similar frequency counter including the proto PCB made by JLC).
Practically eliminate means 100 picoseconds range that is so minuscule compared to the jitter from the GPS pulse output that one can entirely focus on that (getting rid of the added variance of the GPS pulse output).

Hi Edigi,
Some people think jitter from GPS module is not so important because when You averaging it to control let say OCXO with 100 second,  the jitter will attenuate so much especially when You use TIC but in my opinion there is nothing wrong with the best we could.
as far as I know TDC7200 can work up to 50MHz but I do not know how much trouble for You for multiply I assume 10MHz source to 50MHz even sampling 1PPS with 10Mhz will very good.
 

Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #35 on: August 10, 2019, 03:39:08 am »
Just an update of where I'm at... I got the TDC7200 working tonight and it works nicely. My Kalman filter seems to work OK too, so next I'll implement a decent control loop. I had one working before with the DAC but it was only rough as a proof of concept. I'll also wire up my 20 bit DAC in place of the 16 bit.

I think I'm hitting the limit of building all of this on breadboards though. I'm getting some spurious signals, triggering the TDC7200 interrupt when there hasn't been a PPS edge to start it. I can only think it's picking up interference from something. I haven't caught what's triggering it on my 'scope yet. The spurious interrupts, when they happen, are always 100ms after a legitimate trigger from the PPS edge. I can't think of anything I'm doing that would give that.

Thebeol, I'm not sure there's anything to gain from multiplying up the 10MHz for TDC7200, if that's what you mean. It has a minimum measurement time of 12ns so at 50MHz, for instance, it would not be able to measure until after half a cycle.

When I have the control loop working well, I might try changing the PPS for a higher frequency (maybe 1kHz) and see if the higher measurement rate improves matters.
« Last Edit: August 10, 2019, 04:00:32 am by Illusionist »
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Offline Johnny B Good

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Re: GPSDO: PLL or MCU controlled?
« Reply #36 on: August 22, 2019, 02:11:46 am »
I realise it's a bit of an imposition to spring such a "left field" question 'out of the blue' on you like this...

Not at all, it's all good. Not that I can be of much help with the matter unfortunately.

One of the few decent investments I made some years ago was a Weller soldering station (the basic analogue temperature control one) and a couple of irons; a WSP80 for general soldering and a WMP65 micro pencil for the fine pitch stuff. I might make a different choice now, but at the time there wasn't as much choice and the Weller does the job perfectly well. It just takes up a bit too much of my very limited desk space.

The bigger WSP80 gets far more use, especially now I've discovered drag soldering. A bit late to the party perhaps, but I'm glad I got there. I persevered for ages with a 0.1mm tip on the micro pencil, soldering 0.5mm pitch ICs a pin at a time under the microscope.

The one bit of advice I would give, given that most interesting things now are SMD, is to get an iron that you can buy a gull wing tip for. They go by other names too and have a concave dish in the tip which holds a tiny blob of solder. I watched a few videos on drag soldering, then gave it a go on some 28 pin TSSOPs. The videos made it look ridiculously easy, and to my amazement it actually was. The flux was critical; I got a bottle of RA flux from Farnell along with the tip. It works much better than my flux pen for this purpose:

https://uk.farnell.com/mg-chemicals/835-100ml/rosin-soldering-flux-bottle-125ml/dp/2903909

I must admit that ublox module was a pain to solder. Making the rest of the board went like a charm (even the 0603 parts that were small enough to carelessly inhale) but that module just sucked the heat right out of the iron before it could make a joint. By the end of it I had turned up the heat to about 330C, iirc, with the WSP80 and was just managing to get good joints made without feeling I was going to overcook it or leave a cold joint. That was before I got that bottle of good flux though, which I think would have made quite a difference in getting the copper to wet. Still, it survived.

Should you change your mind about giving it a go, give me a shout about those spare PCBs.

I've not had chance to do anything with the GPSDO today, other than plot and scheme. As much as I like the (relative) simplicity of a PLL, my original idea was to use an MCU controller. I need one for sync'ing my derived PPS anyway. Using basic frequency locking control of the OCXO on an MCU though isn't conducive to keeping that DPPS where it should be. It drifts, slowly but surely.

It's much easier to use phase locking on the OCXO than to try to keep the DPPS sync'd without it. So... I'm considering doing the phase locking in the MCU, either with a capacitor and ADC or one of those TI chips mentioned earlier in the thread... implementing what I now know is known as a TIC. Along with learning how to use the dsPIC for actual digital signal processing. I could even try pressing the CTMU (essentially a built-in TIC) on the dsPIC to the task, but it seems so unstable I don't know if it's worth the effort.

...and then I wonder if it's all worth the extra effort when I can already get the OCXO more accurate and stable than I'll likely ever need. But that's not the point, I guess.

It's good to have choices  :-DD

 Apologies for the delayed response, I spent the next three days since then researching cost effective soldering stations before placing an order for the KSGER T12 Soldering Station clone of the Hakko with Banggood the night before starting a ten day cruise holiday, returning on the 18th and it's taken me almost three days to catch up with my iplayer downloads and conversion to the more efficient H.264 storage format which reduces the "Never mind the quality, feel the width" profligate transport stream format used by the iPlayer servers down to just under half size with absolutely no discernible impact on video quality. It took two and a half days worth of processing for Handbrake to complete this task and It's only now, after sorting out ebay issues that I've finally been able to start checking out the eevblog threads I've been participating in.

 As a result, I've not had any time to apply myself to the GPSDO project and now I'm having to familiarise myself with the various features of the T12 clone soldering station, notably, calibrating the ten soldering iron tips I'd also purchased to complement the single supplied starter T12-K tip that came with the soldering station. Incidentally, that gullwing tip you described doesn't fit any of the ten T12 tips in my collection but I've no doubt that one or more of the dozens of available tip types in the T12 range will match this requirement.

 I have to say, I'm very impressed with this KSGER T12 unit even though I've yet to use it in anger and that's despite the necessary fettling of the poor assembly and soldering of the T12-9501 handle and some minor fettling of the PSU/Controller box which I had anticipated from the various tear down and review Youtube videos I'd watched. Lucky for me that I already had a modest collection of Antex soldering irons to hand. :)

 I'd specifically chosen the Banggood unit for its T12-9501 handle (and the inclusion of a K type tip to make this a complete starter kit - most other offerings didn't include a soldering tip offering the inferior colletted type handle which counter-productively extends the effective iron tip to finger grip distance).

 Although the T12-9501 handle might look like a cheap plastic handle, it's actually superior in many ways, being both lightweight with speedy pushfit tip changing and the provision of more precise control courtesy of the shortened finger gripping point to soldering tip distance. Anyone thinking of getting one of these soldering stations would do well to choose the "plasticy" T12-9501 handle over any of the other more flashy metal handles being offered.

 I paid just fivepence over 39 quid for this kit but by the time I'd included a soldering iron stand, a wire wool tip cleaner and a set of ten T12 tips, not forgetting a thermocouple soldering iron thermometer, I'd racked up a total order value of some 76 quid. Still, it was well worth shelling out for these 'extras'. :)

 BTW, that bottle of RA flux you linked to on Farnel's site costs three quarters the price of the KSGER soldering station which seems eye wateringly expensive to me. Just how long does a 125mL bottle of this magic RA flux last for?  ::)  ;)

 Thanks for the recommendation and all but I think I'll look for a more economic way to flux my solder joints if you don't mind my saying so (I've still got plenty of sticks of Beeswax left over if I need to flux large areas of circuit board ;D -OJ ).

 I might be able to acquire some of this magic flux at a more favourable price point at my new favourite online shopping site, Banggood - I just haven't looked... I have now and there's a bewildering array of soldering flux related items, none of which relate to RA flux. I guess I'll have to do a google or duckduckgo search to try and track down a cheaper source.

 Never mind, I can always experiment with the unused fluxes I'd bought at last April's radioham rally which I'd simply bought to satisfy an urge to buy anything remotely related to electronics whilst I had the, now sadly rare, privilege of doing a face to face deal with a seller and, of course, I've still got a stock of multicore solder which doesn't normally require a separate application of flux anyway.

 Once I've finished calibrating my soldering iron tips (more like pencils really) and fine tuned the rather comprehensive settings of the KSGER soldering station, I'll be able to turn my attention back to the job of assembling a complete, if basic, GPSDO and put my 76 quid investment in soldering kit to full and productive use.

 I'm now looking forward to a more relaxing soldering session now I don't have to weigh up whether to switch an Antex iron off to avoid premature wear from overheating or leave it on to be ready for the next set of solder joints minutes to hours later.

 I've got it set to idle at 100 deg C after a 5 minute idle time and run up to 280 or 300 deg C (I haven't decided the optimimum temperature setting for the 60/40 rosin cored solder I'm using) within ten seconds of disturbing the 'shake' sensor in the handle. This "direct drive" soldering technology with its tight PID temperature control is a vast improvement over the soldering experience with the basic Antex soldering irons I've been using off and on over the past thirty odd years or so and I'm rather looking forward to using it.

 There may be superior soldering station kit out there but for hobbyist use, this KSGER unit seems to offer the best bang for the buck and Hakko soldering tip compatibility to boot. I rather doubt I could justify the expense of a genuine Hakko soldering station or any of their competitor's offerings so I'll just have to 'jolly well make do' with this cheap clone for the time being. ;D

JBG
John
 

Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #37 on: August 22, 2019, 03:12:31 am »
Sounds like you're keeping busy there!

BTW, that bottle of RA flux you linked to on Farnel's site costs three quarters the price of the KSGER soldering station which seems eye wateringly expensive to me. Just how long does a 125mL bottle of this magic RA flux last for?  ::)  ;)

I had to check... they put the price up, just a little. I must admit I thought it was cheap in comparison to the others... it was £6.90 when I bought it. Must have been an error. As to how long it will last, likely as long as I'll be soldering.

I also bought a pot of this the other day, because I needed something that only Farnell had in stock and wanted to make the order up to £20:

https://uk.farnell.com/mg-chemicals/8342-50g/ra-rosin-flux-paste-37-7ml-50g/dp/3018421

It's £6 a pot, still, and works just as well as the liquid. It's a bit easier to control too. I just paint it on where needed with a sliver that I cut off an antistatic rubber mat.

---------

As to my GPSDO, I now have my derived PPS synchronized to within 500ps of the GPS second (minus its jitter thanks to Kalman). Its phase is adjustable in 500ps steps up to 100ns in front of the second, to account for cable delay etc.

The core design is settled now. I've decided to add a small Nextion display to it for statistics, and use some of the spare dsPIC horsepower to run a couple of user configurable frequencies/PWM outputs. I don't have much desk space, so adding that facility will save pulling my AWG out of the drawer and clearing space for it when I just need a simple source.

The last major thing to do is test my output circuits on the breadboard. They seem fine in Multisim.
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Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #38 on: August 22, 2019, 04:53:52 am »
That bottle of flux that has gone up to £29 for 125ml... Farnell has the 1 litre bottle for £23.

https://uk.farnell.com/mg-chemicals/835-1l/rosin-soldering-flux-bottle-1l/dp/2903910

Someone there can't sort their pricing out!
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Online David Hess

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Re: GPSDO: PLL or MCU controlled?
« Reply #39 on: August 22, 2019, 11:56:25 am »
Kester used to sell flux and other chemicals in 4 ounce glass bottles but they stopped like 20+ years ago.  I have a few marked as 1992.
 
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Offline Johnny B Good

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Re: GPSDO: PLL or MCU controlled?
« Reply #40 on: August 22, 2019, 04:02:13 pm »
Sounds like you're keeping busy there!

 It's always like that after these cruise holidays which the XYL loves so much (I'm not so keen - given my way, I'd rather avoid any such disruption to my own interests - I always feel that I could do with a holiday break to get over the holiday break, a feeling that seems to be shared by many others).

BTW, that bottle of RA flux you linked to on Farnel's site costs three quarters the price of the KSGER soldering station which seems eye wateringly expensive to me. Just how long does a 125mL bottle of this magic RA flux last for?  ::)  ;)

I had to check... they put the price up, just a little. I must admit I thought it was cheap in comparison to the others... it was £6.90 when I bought it. Must have been an error. As to how long it will last, likely as long as I'll be soldering.

 Just a little! Blimey, that's a bit of an understatement! ::)

I also bought a pot of this the other day, because I needed something that only Farnell had in stock and wanted to make the order up to £20:

 I know what you mean. BTDTAGTBTS when I was ordering a 3 cell NiMH replacement battery from CPC a few years ago for my Potterton CH controller - the tagged version was far cheaper than the plug in version used by the controller so tagged version it was. I ripped the tags off and dressed the ends with a fine file and it did the job perfectly - a little too well since the trick of switching off at the mains and wait a few hours with the original Nicad to force a reset no longer works, not even if left off over a long weekend! >:( I'd added a couple of Bosch 40W oven bulbs to that order and still had to find some tat to make up the minimum (pre-VAT) order value to escape the delivery charges.


https://uk.farnell.com/mg-chemicals/8342-50g/ra-rosin-flux-paste-37-7ml-50g/dp/3018421

It's £6 a pot, still, and works just as well as the liquid. It's a bit easier to control too. I just paint it on where needed with a sliver that I cut off an antistatic rubber mat.

 Now, that I could afford but apparently you can do even better with a 23 quid ONE Litre bottle of the magic RA flux from Farnell which works out at just £2.875 per 125mL. It looks like Farnell made a decimal point error in their 125ml pricing calculation. ::) :-//

 I've just taken a closer look at my radioham rally purchases of soldering flux (a small 10g tub of "Duratool" Solder Paste - melting point 38-60 deg C) and a 10ml Yosker flux pen of 'no-clean flux'. Checking the duratool.co.uk web address gave a server not found error but googling took me to CPC/Farnell revealing it to be a current product made in china (as per the sticker).

 Interestingly, it was a little harder to track down information on the Yosker flux pen but I did land up on an Amazon page, and this is the interesting bit, where I spotted a 125ml bottle of that magic RA liquid flux in the "Customers who viewed this item also viewed" section priced, more reasonably at a mere £8.35  ::) There's no doubt about it, that one litre bottle of the stuff being sold for a mere 23 quid on Farnell's site is an unmissable bargain!  ::) :wtf: The only problem, unless I go into the repackaging/profiteering business, is that it's likely to expire its BBD long before I get to use even a small fraction of the contents. :( BTW, can you tell me what its storage lifetime is? I couldn't find any specification on this.

[EDIT]
==========================================================================================
 Belay that last question! I followed the link to the one litre bottle and found my answer in the technical datasheet - it's 5 years after date of manufacture for storage conditions of 18 to 27 deg C. Presumably it could last a lot longer if stored in a fridge (5 to 8 deg C).
==========================================================================================

 Oh, yes, I almost forgot, I did notice that that Yosker flux pen had been given very favourable customer reviews along with a helpful warning to store it upright after first use (it tends to leak otherwise, apparently).


---------

As to my GPSDO, I now have my derived PPS synchronized to within 500ps of the GPS second (minus its jitter thanks to Kalman). Its phase is adjustable in 500ps steps up to 100ns in front of the second, to account for cable delay etc.

The core design is settled now. I've decided to add a small Nextion display to it for statistics, and use some of the spare dsPIC horsepower to run a couple of user configurable frequencies/PWM outputs. I don't have much desk space, so adding that facility will save pulling my AWG out of the drawer and clearing space for it when I just need a simple source.

The last major thing to do is test my output circuits on the breadboard. They seem fine in Multisim.

 My ambitions at the moment are somewhat more modest right now. It'll be good to get a first working DIY GPSDO up and running for the time being (it's only taken me some 6 months or so to get to the threshold of assembling a nice stable version of the breadboarded design onto veroboard and into a handy little metal enclosure). I've got another six of the 12v 10MHz CQE OCXOs going spare (the seventh is already installed in my FY6600 sig genny - they look identical to that 5v 13MHz one I'm using in the current project) which I plan to use in more ambitious future GPSDO projects. ;)

JBG
« Last Edit: August 22, 2019, 04:14:25 pm by Johnny B Good »
John
 

Offline Johnny B Good

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Re: GPSDO: PLL or MCU controlled?
« Reply #41 on: August 22, 2019, 04:56:17 pm »
That bottle of flux that has gone up to £29 for 125ml... Farnell has the 1 litre bottle for £23.

https://uk.farnell.com/mg-chemicals/835-1l/rosin-soldering-flux-bottle-1l/dp/2903910

Someone there can't sort their pricing out!

 Indeed! Working out the price per 125ml from the 1l bottle price, one might almost be tempted to think they'd shifted the decimal point one place to the right by mistake in their calculation (force of habit maybe? ::) ) Still, it's only just over three times its price on Amazon. >:D Perhaps Farnell have deliberately over-priced the 125ml bottles to tempt prospective customers into purchasing the 1 litre bottles before they exceed their DOM 5 year limit and become unsaleable.

 I did briefly consider the possibility of purchasing a "Lifetime's Supply" until I considered the probable issue of a limited storage life putting a big dent into that plan. I rather fancy that even storing the bulk of a 1 litre bottle's worth in the fridge to get a ten year or longer shelf life would still leave me with a sizeable unused surplus even if I were to be profligate in my use of the stuff so quashed all thoughts of spending 23 quid with Farnell.

 Buying such 'consumables' in smaller quantities, as and when the need arises, seems a far more sensible plan in this case. Besides which, at this stage of the game, there's little point in buying the larger, more economic quantities until I have a better idea of my actual usage rate, plus it's better to have a small range of solder flux types better matched to any individual usage cases that arise. In any case, I won't be spending my money on luxury items such as that 29 quid 125ml bottle of magic flux from the likes of Farnell. >:D

JBG

John
 

Offline Johnny B Good

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Re: GPSDO: PLL or MCU controlled?
« Reply #42 on: August 23, 2019, 03:38:55 pm »
Kester used to sell flux and other chemicals in 4 ounce glass bottles but they stopped like 20+ years ago.  I have a few marked as 1992.

 Which rather begs the question, are they still within their BBD? >:D I take it that this stock of ancient flux of yours hasn't presented you with any issues over expired BBDs or DOM life expiry limits?

 Talking of soldering kit of such vintage, I was browsing the soldering section of Banggood's site just a few minutes ago (as one does) when I spotted this rather neat item (obviously no BBD issues here ;) ) :-

https://www.banggood.com/Hand-Soldering-Iron-Stand-Helping-Clamp-Magnifying-Tool-Auxiliary-Clip-Magnifier-Station-Holder-p-1017105.html?rmmds=detail-bottom-alsobought__16&cur_warehouse=CN

 Which looked oh so familiar :palm:  Familiar indeed because I already have one to hand which has mostly been gathering dust on the shelf of a roller blind cupboard (never ever closed, btw) in my office/man-cave/workshop for the past two to three decades. :-[ If I didn't already possess the exact same aid, I would have placed an order with Banggood right there and then!!!

 That's obviously had at least a three decades long production run (possibly even half a century or longer!) which is unusual to see with Banggood stock. The annoying thing is that I must have struggled many a time over the past twenty or thirty years, soldering small items and circuit boards without its aid - talk about old habits dying hard! :palm:

 When I first clapped eyes on those pictures of that "Helping Hands with magnifying glass stand", I did briefly consider whether they'd employed an agent to sneak into my man cave to dust mine off and take all those photos. :)

 I'm surely not alone in having such a  :palm: experience? I mean, it's a little embarrassing in a way to admit to such a protracted oversight (twenty or more years worth!) but I feel it's better to have a laugh about it rather than silently mope over allowing such a useful aid to go unused for all those years simply through the sheer force of (dumb) habit.  ::)

JBG
« Last Edit: August 23, 2019, 05:51:58 pm by Johnny B Good »
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Offline Dbldutch

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Re: GPSDO: PLL or MCU controlled?
« Reply #43 on: August 24, 2019, 09:24:57 am »
Illusionist, since you seem to have some spare development boards available, would you mind publishing the circuit diagram for them? It’s early days for me in this process, but I might be interested in buying one from you.

Tks,

Paul
 

Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #44 on: August 24, 2019, 11:49:38 am »
Paul, I haven't published the diagrams here only because I made a mistake with the design. The mistake doesn't effect me at all, and might not effect you, but I didn't want to publish a board with a mistake on it.

That said, I'll PM the files to you later today for you to look at, and I'll point out the mistake. If you still want one, you can have a board for the cost of posting it.
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Offline Theboel

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Re: GPSDO: PLL or MCU controlled?
« Reply #45 on: August 24, 2019, 01:24:38 pm »
@ illusionist
I interested in Your kalman filter implementation can You tell more about it please.
 

Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #46 on: August 24, 2019, 04:34:58 pm »
Theboel, here's my Kalman filter code. I'm hardly an expert. Despite (or perhaps due to) having studied electronics, geology and chemistry at university, I've always been allergic to statistical mathematics. My code is the result of a few days' research on the internet, a.k.a. borrowing other people's solutions. I found www.kalmanfilter.net particularly easy to follow for a basic understanding.

I've added an 'Initial Guess' to the filter initialization, which I give the first reliable reading from my TIC when it's near enough to be useful (Edit: to clarify, when I have coarse-tuned the DPPS to be close enough to the PPS for the TIC to take over). It just saves the ramp-up that the filter does otherwise.

The numbers I send to the filter are the time intervals between the GPS's jittery PPS and my, more stable, derived PPS. I scale the readings as floating point in nanoseconds. The 'raw' DPPS is set to be 100ns in front of the PPS to allow adjustment with the delay line, which gives the final output.

Code: [Select]
	
// Single dimension Kalman filter with process variance noise

float KF_Estimate_Uncertainty;
float KF_Measurement_Uncertainty;
float KF_Q;
float KF_Gain;
float KF_Last_Estimate;
float KF_Current_Estimate;

// KF_Init(Measurement Uncertainty, Estimate Uncertainty, Process Noise Variance, Initial Guess)

void KF_Init(float SetMeasurementUncertainty, float SetEstimateUncertainty, float SetQ, float SetInitialGuess) {
KF_Measurement_Uncertainty = SetMeasurementUncertainty;
KF_Estimate_Uncertainty = SetEstimateUncertainty;
KF_Q = SetQ;
KF_Last_Estimate = SetInitialGuess;
}

float KF_UpdateEstimate(float ThisValue) {
// Gain update
KF_Gain = KF_Estimate_Uncertainty / (KF_Estimate_Uncertainty + KF_Measurement_Uncertainty);
// State update
KF_Current_Estimate = KF_Last_Estimate + KF_Gain * (ThisValue - KF_Last_Estimate);
// Extrapolate estimate uncertainty, with process noise
KF_Estimate_Uncertainty =  (1.0 - KF_Gain) * KF_Estimate_Uncertainty + abs(KF_Last_Estimate - KF_Current_Estimate) * KF_Q;
// Record estimate for next iteration
KF_Last_Estimate= KF_Current_Estimate;

return KF_Current_Estimate;
}

« Last Edit: August 24, 2019, 04:40:05 pm by Illusionist »
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Offline IllusionistTopic starter

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Re: GPSDO: PLL or MCU controlled?
« Reply #47 on: August 24, 2019, 04:51:56 pm »
I should also add to the above:

The Kalman filter isn't started until the DPPS and PPS are close enough for the TIC to be useful. Then, I let the filter run until the returned estimates have settled (iirc to within 200ps) before I start using them to fine-tune the DPPS phase using the delay line.

After that adjustment, I let the filter settle again at its new value before entering a monitoring stage.

The monitoring stage makes single delay step adjustments to account for small changes. These keep the DPPS within 250ps of the filter-estimated PPS time. These adjustments are few and far between once the GPSDO has been running for an hour or so.
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Offline Gandalf_Sr

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Re: GPSDO: PLL or MCU controlled?
« Reply #48 on: October 24, 2019, 12:06:39 pm »
Illusionist, The GPDSO design is interesting.  I sent you a PM about coming up with an open-source PCB design.
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Online David Hess

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Re: GPSDO: PLL or MCU controlled?
« Reply #49 on: November 12, 2019, 02:51:09 pm »
Kester used to sell flux and other chemicals in 4 ounce glass bottles but they stopped like 20+ years ago.  I have a few marked as 1992.

Which rather begs the question, are they still within their BBD? >:D I take it that this stock of ancient flux of yours hasn't presented you with any issues over expired BBDs or DOM life expiry limits?

It raises the question.  Begging the question is something completely different.

The Kester 44 flux is as good as it ever was so far as I know.  The Copper-Nu has an indicator which has not changed and it works great also.  Various thinners and solvents are subject to evaporation but not degradation.

Quote
Talking of soldering kit of such vintage, I was browsing the soldering section of Banggood's site just a few minutes ago (as one does) when I spotted this rather neat item (obviously no BBD issues here ;) ) :-

https://www.banggood.com/Hand-Soldering-Iron-Stand-Helping-Clamp-Magnifying-Tool-Auxiliary-Clip-Magnifier-Station-Holder-p-1017105.html?rmmds=detail-bottom-alsobought__16&cur_warehouse=CN

Which looked oh so familiar :palm:  Familiar indeed because I already have one to hand which has mostly been gathering dust on the shelf of a roller blind cupboard (never ever closed, btw) in my office/man-cave/workshop for the past two to three decades. :-[ If I didn't already possess the exact same aid, I would have placed an order with Banggood right there and then!!!

I have one of those that is at least that old.  I reinforced the alligator clips where they insert into the holders with brass tubing to keep them from bending when the screws are tightened and made some more clips like that in different sizes.
 
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