Starting with 1r9, I'm breaking up the source files as the project
is getting too big.  The Arduino IDE will assemble all .ino files in 
the dirctory as one big file, no modifications needed.

  SimpleSNA_***etc***.ino

This is the main file and one you should open to compile the program.
It contains the comments and revision notes and all global declarations,
#defines, EEPROM declarations, etc.  The setup() and loop() functions
are in this file.

  generator.ino

Contains only the generator() routine, when the Generator option is
selected from the menu.

  SNA.ino

Contains the sweep() function which is called when the user selects
the SNA Function option.  Asks the user for limits and step size, then
runs the sweep, returning frequency and dBm at each step in CSV format.

  calibrations.ino

1) This file interacts with the user to find the actual internal clock
frequency on the DDS board, then will save it to EEPROM. This causes
the DDS to be calibrated.

2) Also in this file is the routine to calculate the AD8307 constants,
meaning that it determines the slope and intercept for the AD8307
meter.  The user must input two or more known dBm levels in an
interactive process.  The opportunity to save the constants to EEPROM
is offered.

  eeprom_i_o.ino

This file has routines to save information to EEPROM and to retrieve it.
Includes slope & intercept, reference clock frequency, and start-up
frequency.  Note that there are some routines elsewhere in the project
that have their eeprom I/O embedded in their routines.  Note the EEPROM
register definitions are in the main project file.

  crystal.ino

This file has the routines needed to characterize a crystal:  find it's peak
(resonant frequency), crystal loss at resonance, test fixture loss, and
Lm, Cm, and Rs for the crystal.  Also allows saving the test fixture loss to
EEPROM.

  PLX_SWEEP.ino

This function interacts with an Excel spreadsheet under control of the
PLX-DAQ macro.  Allows PHSNA to send data directly to a spreadsheet with
no terminal program required.

  startup_modes.ino


This file has some routines that set the modes the PHSNA software will start
up in.  Routine set_startup_fq() asks the user for a desired start-up 
frequency, then offers to save it to EEPROM so it will start up there every
time.  Routine set_startup_mode() allows the user to choose to start up in
the PLX-DAQ (Excel spreadsheet) mode or the normal "terminal" mode. Routine
toggle_DDS_mode() allows the user to choose whether the PHSNA Arduino will
start up expecting to control an AD9850 chip, or an AD9851.

  misc_functions.ino

This file has some short unrelated but important functions.  The PROGMEN
functions are alternate serial print functions that store strings in flash
memory.  In this way, they don't use up RAM.  Strings normally take up RAM
space, which is at a premium in the Arduino.
clear_serial_buffer() does that.
tfr_byte(byte) sends a bute to the 9850/9851
sendFrequency(double) calculates the phase increment and sends it to the DDS
chip. Also sets f_out to the frequency argument.
float counts_to_dbm() takes the stored slope and intercept and CH0_ADC_counts
and converts to dBm, returning that number.  It also does the frequency
compensation / normalization thing if polynomial cofficients are set up.
options() is a function that generates the sub-menu for calibrations, etc.





