[minima] Re: Si570 error: linear with frequency
- From: Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Fri, 7 Feb 2014 01:12:40 -0800
Thanks Steve, great resource. Started a new wiki page for the si570:
http://www.hfsignals.org/index.php/Si570
One tip for everyone: Write down the markings on your si570 before you glue
them dead-bug style... I am lucky I had two of them.
My SI570 is a CAC000141G. I found online (and by measuring the output
frequency without the arduino) that my startup frequency is 56.320. The
datasheet does not seem to include the table which links "000141" to 56.320
Mhz. If someone has that, we should put it on the wiki. I am sure other
people will need it.
With that info, and if I read the register values HSDIV, N1 and RFREQ at
startup, I can calculate the internal crystal frequency using the formula:
FXTAL = ( fOUT x HSDIV x N1 ) / RFREQ
Ideally, the minima software should ask me to choose which si570 I have in
a list when I start it for the first time. It would then do the math and
save that in the eeprom. I am going to create a "bug" for that on the
project: https://github.com/afarhan/radiono/issues/3
Right now, you have to manually extract HSDIV, N1 and RFREQ and calculate
fxtal and save it in the source. I will try that tomorrow.
thomas
On Fri, Feb 7, 2014 at 12:49 AM, Steve VK2SJA <vk2sja@xxxxxxxxxxx> wrote:
> I was only half right. Which means I was half wrong! :-)
>
> This document contains VERY good overview of Si570 operations:-
>
> http://cbjohn.com/aa0zz/PPLL/Article.pdf
>
> See section on calibration.
>
>
>
> > this is to do with the correct setting of the crystal frequency in the
> > radiono.ino. it has to be adjusted so the tracking is linear.
> >
> > - f
> >
> >
> > On Fri, Feb 7, 2014 at 1:25 PM, Steve VK2SJA <vk2sja@xxxxxxxxxxx> wrote:
> >
> >>
> >> These Si570's appear to be available with lots of different start-up or
> >> clock frequencies. i admit to being a bit confused about the
> >> relationships
> >> startup vs clock here. But you can arrive at the start up frequency from
> >> the part number. See the chip datasheet part ordering section for
> >> details.
> >>
> >> Suggestion. Apply power to Si570 chip while disconnected from I2C. To
> >> make
> >> sure software does not change frequency. Measure frequency output.
> >>
> >> Change code line below to match your default power up frequency:-
> >>
> >> #define FREQ_XTAL (114292532l)
> >>
> >> What does it look like now?
> >>
> >> Yes I think we are going to need a once only setup routine in firmware.
> >> Si570 chip seems to store stuff like the startup frequency in registers.
> >> Unclear at this point if we store offset data in NV storage in AVR or if
> >> you can update Si570 registers. Still reading... Learning...
> >>
> >>
> >>
> >> > Hi,
> >> >
> >> > I finalized the digital board tonight and was checking the output
> >> > frequency
> >> > of the si570 and I found a somewhat important error which seems to be
> >> > related to the vfo frequency.
> >> >
> >> > [image: Inline image 1]
> >> >
> >> > This error seems to be linear and could easily be corrected in
> >> software
> >> > but
> >> > for example when I set 14.200 on the VFO, my frequency meter counts
> >> > 34.2133
> >> > mhz.
> >> >
> >> > Is this something you are seeing as well? Should we add a calibration
> >> step
> >> > to measure and correct this error? Or is my Si570 just bad?
> >> >
> >> > Full measures here:
> >> >
> >>
> https://docs.google.com/spreadsheet/ccc?key=0As9CZnZ-A5a2dEZaM1dlWVdVX3pXaUlJMXd0cHNscHc#gid=2
> >> >
> >> > cheers,
> >> > thomas
> >> >
> >>
> >>
> >>
> >>
> >
>
>
>
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