Specification

[Bob]

Initial Spec:

Powered from external 12-24Vdc supply.

Runs stand alone or via character based command line interface
available via serial (RS 232) or ethernet (telnet) (Choice TBD by
builder). Internal interface is TTL serial. Interface slot can hold
one card providing one of:
RS232 level shifter,
USB<-> Serial interface (FTDI or equiv)
Serial <-> ethernet card (telnet interfce)
Serial <-> ethernet card (http interface).
GPIB controller

Uses internal timebase. Low cost option is xtal bases osc module. TCXO
option or external 10mhz reference standard, sine or ttl as
alternative to internal timebase.

Four inputs: External timebase (above), Arm, A & B.
Arm input may be used to disable either/both inputs.

Inputs are ttl compatible, rising edge triggered. Later additions may
include input filtering such as: AC/DC coupling, 50ohm/1Mohm
impedance, variable attenuation, prescalers, trigger on edge or level,
over voltage protection, <add list here>

Provides the following functions:
Time interval A->B
Frequency A
Width A
Events A during B
Period A
Count A
Count A +/- Count B
Possible additional functions:
Rise/fall time A
Average of any of above
Ratio A/B

Goals:
Frequency: 20Ghz w/o external prescaler.

Time Interval resolution: 25ps

Build cost < $200 not including power supply, case, or interface
other than RS-232 for initial run of 25 units.

Use only SMT, SMD packaging. Avoid through hole when possible. No
BGA packaging. Must be assemble-able by skilled amateur with soldering
iron, 20x magnification, solder/solder wick, other common tools.

All components must be available internationally. Vendors who will
sample parts are preferred.

Built with conventional, 2 layer pcb wherever possible.

Design guidelines:

Modular design. Separate control and front panel from core
counter, counter from input. Modules interconnect with commonly
available connectors such as 0.1" space inline.
Code for internal processors to be written in C or VHDL
Counting should be direct where possible, via hardware division
where possible, interpolation elsewhere.
Schematic capture and PCB design with EAGLE.
PCB's to be made available through group buy, parts list to be
available on group, build instructions on group.