[time-nuts] WWVB teensy BPSK early experiments

Wed Nov 11 02:50:17 UTC 2020

Hello Time Nuts,

I've been running some tests - I just had the screen 'white-out' problem
happen again - I have a termination resistor on the SCK line (pin 13 on the
Teensy 4.1) -
so it appears this is related to the TFT screen updates - maybe a pixel
write going out of bounds.  The Teensy is still running - but the screen
can't be read.

Note the current code I'm testing is here in case anyone is interested -
it's from the PJRC forum:
https://github.com/jwestmoreland/el_supremoWWVBsdr

73's,
John
AJ6BC

On Tue, Nov 10, 2020 at 10:43 AM paul swed <paulswedb at gmail.com> wrote:

> Graham that is the alternate approach. The new suggested KD2BD vcTCXO works
> very well. Its 10 MHz and readily available. But then the old divider
> chains are needed. The KD2BD method works well if you have plenty of
> solder.
> First mixer is 50 KHz LO. Result 10 KHz IF.
> 10 KHz IF gain
> Second Mixer is a 10 KHz LO results in a 0 Hz IF.
> But the products are actually phase offset and bit.
> The above comments are seriously over simplified.
> Having built the KD2BD receiver I am interested in a low solder solution.
> :-)
> Really have to do far more experimentation. The teensy is very powerful.
> Regards
> Paul
>
>
> On Tue, Nov 10, 2020 at 12:56 PM Graham / KE9H <ke9h.graham at gmail.com>
> wrote:
>
> > Paul:
> >
> > It might be easier to relegate that function to hardware.
> > A simple TC-VCO that drives the sampling clock for the ADC and is
> steerable
> > for frequency/phase lock from the CPU would allow you to build a
> > synchronous receiver without working about locking the CPU clocking
> system
> > to anything.
> >
> > --- Graham
> >
> > ==
> >
> > --- Graham
> >
> > On Mon, Nov 9, 2020 at 8:06 PM paul swed <paulswedb at gmail.com> wrote:
> >
> > > No time to experiment the last few days as the weather has been great
> and
> > > have to get outside stuff done. That said trying to tease apart how to
> > > create a lockable NCO in the teensy.
> > > Its not clear to me that I can create a sine wave oscillator and drive
> > that
> > > out to a pin to see stability and adjustment effects. It can be done by
> > > mixing with another internal signal and measuring the output. But my
> > > preference would be direct measurement.
> > > With respect to sine and cosine. It seems a second oscillator and a
> third
> > > oscillator that is 90 degrees out can be created. Supposedly these
> would
> > be
> > > locked. (To be proven)
> > > Regards
> > > Paul
> > >
> > >
> > > On Sun, Nov 8, 2020 at 7:59 PM John C. Westmoreland, P.E. <
> > > john at westmorelandengineering.com> wrote:
> > >
> > > > Hello Graham and Fellow Time Nuts,
> > > >
> > > > I did what Paul had mentioned as well - and that appeared to clear up
> > the
> > > > immediate screen issues but I will
> > > > insert a termination resistor as well as Graham has suggested.
> > > >
> > > > I looked on the PJRC forum as well - and it appears there has been a
> > lot
> > > of
> > > > discussion and development regarding
> > > > the enhancement of the performance of these TFT displays - also -
> > > there's a
> > > > beta version of the arduino libraries -
> > > > Teensyduino 1.54 Beta #4 -
> > > > https://forum.pjrc.com/threads/64303-Teensyduino-1-54-Beta-4 - take
> a
> > > look
> > > > at that
> > > > for those that are experimenting with this platform.
> > > >
> > > > As far as my current setup - in the wee hours today - the WWVB signal
> > was
> > > > coming in very strong - my HPSDR rig
> > > > using the Clock tool from Multipsk was decoding every minute - the
> > Clock
> > > > programs' PLL was solidly locked.
> > > >
> > > > I noticed for the Teensy4WWVBsdr code it appeared to be in sync with
> > > WWVB -
> > > > it was decoding either a minute or
> > > > the hour apparently correctly - but it was shifted - meaning say for:
> > > >
> > > > 2:38:00 AM it decoded 2 as the minute - which was incorrect but
> correct
> > > for
> > > > another time position
> > > >
> > > > or, for the hour it would say 8 as hour.  This makes me think
> obviously
> > > for
> > > > some reason the positions are being
> > > > shifted in an otherwise somewhat successful decode attempt.
> > > >
> > > > I am using the Teensy 4.1 - I need to check all of the libs to make
> > sure
> > > > nothing incompatible is possibly taking place.
> > > >
> > > > I've been informed also the antenna from Stormwise is on the way.
> > > >
> > > > Thanks again Graham - KE9H - for helping out on this.
> > > >
> > > > 73's,
> > > > John
> > > > AJ6BC
> > > >
> > > >
> > > > On Sun, Nov 8, 2020 at 8:02 AM Graham / KE9H <ke9h.graham at gmail.com>
> > > > wrote:
> > > >
> > > > > John W:
> > > > >
> > > > > Regarding your Teensy WWVB receiver display issues.
> > > > > The Teensy does not have a source termination resistor on the SPI
> > > clock.
> > > > > Add a 50 Ohm resistor (value not critical, anything from 33 to 75
> > will
> > > > > work) in series with the SPI Clock signal, as physically close to
> the
> > > > > Teensy as practical.
> > > > > This totally cleared up all of my display issues.
> > > > >
> > https://www.analog.com/media/cn/training-seminars/tutorials/MT-097.pdf
> > > > > Source termination resistors provide a source resistance to absorb
> > the
> > > > > reflection of fast edges off the slave device input, reducing all
> the
> > > > > bouncing and wiggles on the rising and falling edges of signals,
> > > > > particularly important/beneficial on clock signals.
> > > > >
> > > > > --- Graham
> > > > >
> > > > > ==
> > > > >
> > > > >
> > > > > On Wed, Nov 4, 2020 at 10:55 AM John C. Westmoreland, P.E. <
> > > > > john at westmorelandengineering.com> wrote:
> > > > >
> > > > > > Paul/Chris,
> > > > > >
> > > > > > Also - in addition to the white screen, I get this sometimes
> after
> > > > > running
> > > > > > for a while - have you guys seen this?
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://user-images.githubusercontent.com/2308903/98118247-cd4c7b00-1e5f-11eb-8510-aa1ed0beba52.jpg
> > > > > >
> > > > > > 73's,
> > > > > > John
> > > > > > AJ6BC
> > > > > >
> > > > > >
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