I promised to post some details on my current Nixie nightmare. I present:
The BRS Clock
The current version of the clock is in 2 (or more) PCBs. This was done to
allow changes to the display type by only either changing the display board
or the display cluster boards. The board can be used with Nixie tubes (10
cathode or 14 cathode “British Flag” types), LEDs, possibly VF or other.
The CPU board:
A pair of 16 pin headers on top of the CPU board connects it to the
display. The CPU supplies 12V, 5V and 170V with the 170 able to be margined
by the CPU. I2C connects “things” on the display to the CPU. The time data
is sent in a serial format (clock+data) along with a transfer strobe to
write the data to the tubes. For Nixie displays, the HV5812PJ-G chip does
direct drive to the cathodes, there is no multiplexing. Additional signals
include a room light sensor an 11 pins defined for control like decimal
points, symbols and “pimp lights”.
The CPU is currently a Silicon Labs C8051F360
Time base. There a 4 possible time base sources for the clock. In
increasing accuracy order:
The CPU time base: This is the worst but with some work can be trimmed up
somewhat. If this is the only time base, the clock will lose time in a
power failure.
AC line clock: The primary power source is 12V. It can be AC or DC. If the
power source is 12V AC, the line frequency is sampled (50 or 60Hz detected)
and used to run the clock. The AC line has good long term stability, much
better than the CPU clock. As with the CPU clock, a power failure will
reset the clock date/time.
DS3231S: This Maxim chip along with a coin cell has very good accuracy and
will remember the date/time during a power failure.
GPS: An optional Trimble Lassen GPS receiver can be plugged onto the CPU
board. It provides a very accurate 1PPS signal and UTC date/time for the
highest accuracy. Other GPS receivers that support the NMEA sentence
structure and a 1 PPS signal could also be used. The GPS has a battery
backup to allow faster cold starts.
6 pushbuttons (plus reset) allow user setting of date, time and setup
parameters. The parameters are saved in EEPROM so are available after a
power-down. 1 button sets/unsets DST so the twice a year change is simple.
There are a number of connectors to plug in various external devices. They
are
Indoor temperature/humidity: A small sensor will allow the display the
indoor temperature and humidity every 5 minutes.
Outdoor temperature: A different small sensor will display the outdoor
temperature at the same time as the indoor, if connected.
PIR/room light: A Passive IR motion sensor and room light level sensor will
allow shutdown in darkness when no-one is around. The room light sensor can
adjust the brightness of the pimp lights automatically.
MP3 player: A simple MP3 player is connected to play different sounds at
different times. The current code plays the Westminster Chimes on the
quarter hour and the hour count at the top of the hour. Many other things
could be done.
Meter DAC: My friend wanted a “Steam Punk” look to the clock so we
incorporated 3 D/A converters (12 bit accuracy) driven at a 1/10 second
update rate with the H/M/S. He will use these to drive vintage large analog
meters so the time will be read as analog.
Stopwatch: Another request was for a work clock that displayed a running
stopwatch every 5 minutes. Three control switches are provided to
start/stop/reset the stopwatch.
Displays
The displays are mounted on a daughter card plugged into the CPU. This
allowed me to only modify the display to run with a number of different
display types. The following information is for Nixi display tubes.
Tubes: Designed using the ‘QTC’ concept from pvelectronics in UK. This
mounts the tube (solder or socket) on a small PCB that plugs into the
display board with a 12 pin 0.1” connector. I have created adaptors for
about 8 or so different tubes. New tubes are quick to create. The original
used IN-14 + IN-19 tubes
Bottom lights: These lights shine thru the base of the tube thru a hole in
the QTC board. I call these “pimp lights” and come in 2 flavors; a standard
single RGB LED that cycles automatically thru multiple colors and a
dedicated WS2812B RGB LED that is individually programmed with 256 levels
of each color. The WS2812B is currently programmed to cycle thru colors
once a minute (seconds), once an hour (minutes) and once a day (hours). For
example, on the seconds, the color starts at 100% red at 00. The red drops
and the green rises and a 1/10 second rate until at 20, the light is full
green. Green then drops and blue comes up so that at 40, it is 100% blue.
Blue then drops and red comes up so that at 00, we are back to 100% red.
Pimp lights are lead zero blanked with the tubes, depending on the selected
lead zero blanking (LZB) mode.
Symbols: If a compatible symbol tube exists, it is installed to the right
of hours, minutes and seconds. When the time is displayed, the symbols
display H/M/S. When displaying temperature, they display F/% (temp and
humidity) in other modes they are blanked.
Display boards: there are currently 3 display boards; small, large and
cluster.
The small display board was designed for the IN-14 digit/IN-19 symbol
tubes. With the QTC changes I have operated other tubes such as the B-5750.
The large display board was for bigger tubes like the Z560M digits/IN-15
symbols. It could also work for IN-12 digits.
The cluster display was created to allow different sizes of displays to be
quickly created. The concept is that a hub board is plugged into the CPU.
The hub then splits off to 3 20 pin ribbon cables, 1 each for H/M/S.
Plugged into the far end of the cable is a display clusted board that holds
the driver and QTC sockets for 3 displays. The common hub exists and a
cluster has been designed for the Z560M digits/IN-15 symbols. The cables
ease the mounting requirements for larger displays. It should also work
well for the upside-down HP displays
Open Source: I am not making this a business. I usually fab more boards
that I need and some down-level stuff exist. I am willing to share what I
have and know so I will supply the schematics (OrCad/PDF), PCB layout
(allegro/gerbers) and code (8051 assembly language). If you need some other
display adapted (Panaplex, LED etc) let me know. If it interests me
(semi-retired) I can help or make suggestions. All of these boards are
surface mount based. The smallest part is 0603 so not super small. If
needed, I could solder tough parts that require a fine tim or hot air mount
the 2 parts that need it.
If you have any questions, want documentation or availability, let me know.
I am a master of questionable answers (or was that answerable questions?).
Always glad to get a question starting with “could you…..” or have you
ever….
-Other Bill-
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