[time-nuts] E1938A source code/ firmware

[Glen English VK1XX]

OK, good info, thanks.

Well I have bought 7 x E1938As, with the intention of building a better 
GPSDO.

My interest in the E1938A firmware hex was if I had to replace any of 
the PICs at sometime in the future.

My intention is to use the average of multiple stationary mode GPS 1PPS 
signals to drive a single OCXO, the idea to be a better 1pps estimate. 
I'll upsample the inputs to get the control sample rate up.

Eventually I want to explore the use multiple OCXOs, but not until I 
think of a good way to take an average of multiple OCXOs, or, even if 
that is a useful idea.

FPGA based,  I'll  put the OCXO drive and the 1ppS to the FPGA 
differentially into maybe  8 FPGA inputs (that is each signal into 8 
different FPGA pin pairs) , and use IDELAY blocks to delay the 8 
different inputs to provide more edge resolution for each signal . The 
IDELAY blocks can be dynamic but I'll probably use then fixed. output of 
the FPGA can be sigma-delta converter, which can provide almost 
arbritary number of bits. LVDS output of the 1 bit FPGA converter signal 
will go to an outboard LVDS buffer with its own power supply so bumps on 
FPGA  VCCIO dont affect the output.

So first, I'll need to build a frequency/period  counter in the same ilk 
(same PCB)

I'll make these PCBs loaded available to all.

I have a protoype built and output at the moment is HD44780 LCD drive 8 
bit bus to  surplus 40x4 char displays I have around here. and also a 
serial stream output. best to do only what is necessary on the FPGA 
(rudimentary time/frequency output onto the LCD) , and feed data to an 
analysis machine, RPI, PC whatever for analysis and display in Python 2.7X.

comments welcome.

-glen  VK1XX / AI6UM

On 6/07/2019 10:06 PM, Adrian Godwin wrote:
> I would agree that antiwindup is important when you have integrators. They
> always seem to cause trouble without it, in applications as diverse as car
> throttle control and time-domain filtering of respiratory data.  I would
> also recommend, sometimes, the use of feed-forward control to provide an
> estimate of power demand without relying on the integrator : although most
> useful for speeding the response, it can also reduce th