Divergence Meter Project

Operating Instructions

The device has two control buttons on the back: "button 1" and "button 2." The device can recognize a "short press" (anything shorter than one second) and a "long press" (anything over one second -- the display often turns from dim to bright when the long press has been held long enough) of button 1. I have not implemented any long presses of button 2.

There is also a slide switch on the back of the unit that engages the internal 9-Volt battery. This switch should be turned on ONLY when the device is not connected to external power!

When powered up, the device starts out in Clock Mode (to prevent the device from displaying a static number for a long period of time after an unattended power outage/restore). You can get from Clock Mode to Divergence Meter Mode by pressing button 1. The device then displays the Steins Gate world line number 1.048596 on the tubes. You should NOT leave the device displaying any static number for an extended period of time because this can lead to 'cathode poisoning' of the digits in the nixie tubes (sputtering from illuminated digits can cause buildup on the unused digits' cathodes, and eventually they will not display properly). It is best to leave the device in Clock Mode when you are not actively playing with it as a Divergence Meter.

The instructions below explain each mode and how to switch between them:

Clock Mode

The device will display the time as hh..mm..ss where the ".." indicate the two decimal points in tubes 2 and 5 (the tubes are numbered 0 to 7 from right to left). Only one decimal point is on at a time in each of tubes 2 and 5, and they switch back and forth every second. The user has the option of 12-hour or 24-hour time display format (see settings). At 30 seconds after the minute, the device will rapidly exercise all of the digits in the tubes for a second, and then display the Date for a few seconds. (The exercising of the tube digits is necessary to prevent 'cathode poisoning' in the tubes). At 59 seconds, the time will be scrolled out of the display to the left, and the new time display will be scrolled in from the right for the start of the next minute. At the top of the hour, there is additional divergence-meter-like animation of the digits.

Button 1: Goes to Divergence Meter Mode 1

Button 2: Goes to Date Mode (and then automatically returns after a few seconds).

Divergence Meter Mode 1

Displays randomly-generated world line numbers.

Button 1, short: Rolls up a random world line number and animates the display of that number. Most of the time it will be an Alpha world line number (0.xxxxxx), but will occasionally be a Beta world line number (1.xxxxxx), and more rarely will be a negative world line number ( .xxxxxx).

Button 1, long: Goes to Divergence Meter Mode 2.

Button 2: Goes to Clock Mode.

Divergence Meter Mode 2

Cycles through 16 pre-loaded world line numbers from the anime and visual novel, with animation. After going through all of the numbers, it returns to Divergence Meter Mode 1.

Button 1, short: Displays the next pre-loaded number in the sequence.

Button 1, long: Goes to Clock Mode.

Button 2: Goes to Divergence Meter Mode 3.

Divergence Meter Mode 3

Allows the user to enter a world line number. After that number is entered, button 1 will alternate between rolling up a random 0.xxxxxx number, and the user's number.

Loading Stage: Starting from the left, the user gets the opportunity to enter each digit.

Button 1, short: Increments the digit being entered. Note that you can enter a 'blank' (empty tube) by incrementing beyond 9, and that the number will rollover back to zero if you increment beyond 'blank.'

Button 1, long: Decrements the digit being entered.

Button 2: Goes to next digit (subsequent tubes are blank until that digit is being entered).

Once the right most digit has been entered, the display will blink several times and then enter the Display Stage:

Display Stage:

Button 1, short: Alternates between displaying the user's entered world line number and a random 0.xxxxxx world line number (with animation) with each press.

Button 1, long: Goes to Clock Mode.

Button 2: Goes to Clock Mode.

Date Mode

The device will display the date in either mm dd yy or dd mm yy format (see settings). The display will automatically return to Clock Mode after a few seconds if no buttons are pressed. If a button is pressed during Date display...

Button 1: Goes to the Brightness Setting (item 11 in the Settings sequence...just to give you a quick way to get there)

Button 2: Goes to the Settings sequence, starting with the Hours Setting. (NOTE! The version number of the software is displayed until you release Button 2 here -- only for code versions 1.04 and later. Normally you will bip right past the display of the version number, but if you want to read it, just hold in Button 2 here for as long as you'd like. Releasing Button 2 continues on to the Hours Setting.)

Hours Setting: 01 hh

The Settings sequence is accessed by pressing button 2 during Date Mode. It begins with the Hours Setting, and continues (via button 2) through the eleven settings.

In Hours Setting, the display shows 01 hh where hh displays the hour in 24-hour format (it doesn't matter whether the user has set 12-hour or 24-hour time display format -- all hour settings are displayed in 24-hour format).

Button 1, short: Increments the hours setting. Incrementing beyond 23 will rollover to 00.

Button 1, long: Decrements the hours setting. Decrementing beyond 00 with go to 23.

Button 2: Goes to Minutes Setting.

Minutes Setting: 02 mm

In Minutes Setting, the display shows 02 mm where mm displays the minutes setting from 00 to 59. If you change the minute setting, the Seconds register is cleared to zero (when you press button 2 to exit this setting). If you leave this setting mode with the minutes setting the same as it was when you entered, the Seconds register will not be changed.

Button 1, short: Increments the minutes setting. Incrementing beyond 59 will rollover to 00.

Button 1, long: Decrements the minutes setting. Decrementing beyond 00 with go to 59.

Button 2: Goes to 12/24-Hour Time Format Setting.

12/24-Hour Time Format Setting: 03 xx

In Time Format Setting, the display shows 03 12 or shows 03 24 depending on whether 12-hour or 24-hour time format has been chosen. Note that even if 12-hour time display format is chosen, all settings menus that deal with hours will show the hours in 24-hour format to avoid any AM/PM ambiguity. The 12-hour time format display does not visually indicate whether it is AM or PM (geez...look outside occasionally). This setting is stored in the PIC processor's EEPROM.

Button 1, short or long: Toggles between 12 and 24 mode.

Button 2: Goes to Day Setting.

Day Setting: 04 DD

In Day Setting, the display shows 04 DD where DD displays the day of the month setting from 01 to 31. And don't be a goofball and try to set February 31 or any nonsense like that (the clock chip will eventually reset any such foolishness). The clock chip automatically knows how many days are in each month, and will rollover properly to the next month.

Button 1, short: Increments the day setting. Incrementing beyond 31 will rollover to 01.

Button 1, long: Decrements the day setting. Decrementing beyond 01 with go to 31.

Button 2: Goes to Month Setting.

Month Setting: 05 MM

In Month Setting, the display shows 05 MM where MM displays the month setting from 01 to 12.

Button 1, short: Increments the month setting. Incrementing beyond 12 will rollover to 01.

Button 1, long: Decrements the month setting. Decrementing beyond 01 with go to 12.

Button 2: Goes to Year Setting.

Year Setting: 06 YY

In Year Setting, the display shows 06 YY where YY displays the year setting from 00 to 99. Note that if the clock chip ever loses battery backup power, the date and time are reset to 12:30 PM on July 28, 2010, a red-letter date for all Steins;Gate fans. Also, the clock chip's backup battery MUST be installed for the unit to work correctly.

Button 1, short: Increments the year setting. Incrementing beyond 99 will rollover to 00.

Button 1, long: Decrements the year setting. Decrementing beyond 00 with go to 99.

Button 2: Goes to Date Format Setting.

Date Format Setting: 07 xx

In Date Format Setting, the display shows 07 00 or shows 07 01 where
00 represents the date format MM DD YY, and
01 represents the date format DD MM YY.
This setting value is stored in the PIC processor's EEPROM.

Button 1, short or long: Toggles between 00 and 01.

Button 2: Goes to Tube Blanking Setting.

Tube Blanking Setting: 08 hh

In Tube Blanking Setting, the display shows 08 hh where hh displays the hour in 24-hour format when the nixie tubes will be blanked. This is accomplished by turning off the high voltage power supply that runs the tubes (the clock continues to run and do various updating...you did remember to leave your device in clock mode when you were done playing with it, right?). By blanking the tubes during hours when you are not using the clock, you can extend the lifetime of the nixie tubes. This setting value is stored in the clock chip's RAM.

Note: If you press either button while the tubes are blanked, the tubes will be un-blanked and will remain on until the next time the blanking hour comes around.

Note: To disable tube blanking completely, set the blanking and un-blanking (see next setting) times to the same hour, and the tubes will always stay on.

Button 1, short: Increments the tube blanking hour setting. Incrementing beyond 23 will rollover to 00.

Button 1, long: Decrements the tube blanking hour setting. Decrementing beyond 00 with go to 23.

Button 2: Goes to Tube Un-Blanking Setting.

Tube Un-Blanking Setting: 09 hh

In Tube Un-Blanking Setting, the display shows 09 hh where hh displays the hour in 24-hour format when the nixie tubes will be un-blanked (the high voltage power supply will be switched back on). Remember: to disable tube blanking completely, set the blanking and un-blanking times to the same hour, and the tubes will always stay on. This setting value is stored in the clock chip's RAM.

Button 1, short: Increments the tube un-blanking hour setting. Incrementing beyond 23 will rollover to 00.

Button 1, long: Decrements the tube un-blanking hour setting. Decrementing beyond 00 with go to 23.

Button 2: Goes to Time Adjustment Setting.

Time Adjustment Setting: 10 xxx

In Time Adjustment Setting, the display shows 10 xxx (or possibly 10 ..xxx) where xxx is the time adjustment setting. This setting can be used to adjust for your clock running fast or slow. The rate at which the DS1307 real time clock chip runs will depend on the specific oscillator crystal you installed, and also upon temperature. My prototype divergence meter, for example, gained about one second every 11 hours. The next main board I built gained one second every 14 hours. If your clock runs fast, you can set a number from 1-255, and the program will drop a second of time every xxx hours. If your clock is slow, decrement the setting value down into the negative numbers (indicated by two decimal points appearing in the tube to the left of the number), and the program will add a second of time every xxx hours. If this setting value is 000 (zero), there is no time adjustment.

To figure out what value to enter, let your clock run (with 000 value entered here) for a few days to see how many seconds it gains or loses over the number of hours you run this experiment. Divide the total number of hours the experiment ran by the number of seconds off the time was, and you will get the value to set. If the clock ran fast, enter a positive value; if it ran slow, enter a negative value. This will give a first-order correction to the clock's time drift. If you notice it drifting faster or slower over time, you can bump the value up or down as needed. Note: This time correction is monitored at the top of each hour, so if you are playing with the device in Divergence Meter mode at the top of an hour, it will miss counting that hour, so the time correction will be a little off. But, in the long run, your device will spend most of its days sitting there in clock mode (with occasional divergence meter fun), so this should work well enough. This setting value is stored in the PIC processor's EEPROM.

Note: A value of 000 indicates that no time correction is being applied.

Button 1, short: Increments the time adjustment setting. (Positive values display as 001 to 255)

Button 1, long: Decrements the time adjustment setting. (Negative values display as ..001 to ..255)

Button 2: Goes to Brightness Setting.

Brightness Setting: 11 b

In Brightness Setting, the display shows 11 b where b displays the tube brightness setting from 0 (dimmest) to 7 (brightest). This setting applies to Clock and Date modes (not to Divergence Meter modes). This can be useful if you find the display too bright at night. It will also extend the lifetime of your nixie tubes to run them at a lower brightness. This value is stored in the PIC processor's EEPROM. The reason this setting does NOT apply to divergence meter modes is because the tubes need to be run at a lower brightness most of the time so that they can be pulsed to full brightness when the world line animation ends.

Note: You can get to this setting quickly by pressing button 1 from Date Mode (no need to scroll through all of the settings).

Button 1, short: Increments the brightness setting. Incrementing beyond 7 will rollover to 0.

Button 1, long: Decrements the brightness setting. Decrementing beyond 0 with go to 7.

Button 2: Goes to Clock Mode.

Power Supply

The divergence meter uses an external "wall wart" power supply. I like the Velleman Compact Universal DC Adapter Power Supply, because it comes with the right size tip (among many) that I needed, and it allows you to set the output voltage. I run my IN-14 nixie tube divergence meter with a power supply voltage of 9 volts. The connector from the DC power supply has a 2.5mm center contact and a 5.5mm diameter barrel. The center contact must be +9 volts, and the outer barrel is Ground. Note that power supplies with interchangeable tips (such as the Velleman supply above) have two ways the tip can be inserted to control the polarity of the tip. If you have the polarity of the DC power supply incorrect, you will at best blow the fuse, and at worst could damage some components in the meter -- so check that your power supply connector is configured correctly.

9-Volt Battery Power

The device has the option of being powered from an internal 9-volt battery. The slide switch to turn on the internal battery power is on the back of the device. DO NOT have this internal battery power switch turned on while the device is using external power, or the power supply will try to charge the battery, and disastrous effects will occur. You have been warned. Yes, you can put a diode in the line from the battery, but this will cause a voltage drop and the device will fail sooner under battery power, so I chose not to do that (but the production boards do have a place to put this diode, after cutting a circuit trace; see the Construction page). You can do that if you think you're the type who might switch the 9-volt battery on while you have the device running on external power.

Also, when no 9-Volt battery is connected, you must not allow the battery connectors contacts to short against any metal parts inside the case. Otherwise, if the 9-Volt power switch is accidentally turned on, your external power supply could be shorted (which would be a bad thing). I use a paper sheath that slides snugly over the connector to prevent this from happening (see the Construction page).

I tested my unit with a brand new Alkaline 9V battery and it ran for about 42 minutes before the processor crashed due to low voltage as the battery discharged. Then again, I tried another new 9V battery, and it ran for less than 10 minutes before discharging. A Lithium 9V has higher capacity (and price) and should run the unit for longer. BUT, this device it primarily meant to be run using external power. The 9V internal battery option is for use for short periods of time only when you need to carry the unit around to impress your friends or when cosplaying as Okabe (hey, nice lab coat) or Suzuha (email pictures to me!). If you need to run the unit for hours of cosplay, you could have a high-capacity 9-volt battery pack in the pocket of your lab coat and run the wire down your sleeve to plug into the unit.

High Voltage Inside!

WARNING: The divergence meter uses 170 volts to drive the nixie tubes. Use extreme caution when handling the circuit boards if you have them powered up, and don't come crying to me if you kill yourself. It is dangerous to handle the bare boards when they are powered up. If you need to run tests on the bare device, plug the power supply into the device's jack, set the device down, and only THEN plug the power supply adapter into the electrical outlet (reverse the procedure when disconnecting the power). When properly assembled in its enclosure, there should be no danger of shock while handling the device. Don't spill your Dr. Pepper on it, of course.

Error Code 666

If the device displays the error code "666" in the tubes, this means the processor is having problems talking to the DS1307 clock chip. Did you remember to install the CR2032 backup battery? The device will NOT work properly without the CR2032 battery installed. Well, actually, you CAN use the device without the backup battery if you stuff a folded up wad of aluminum foil into the backup battery holder so that that line gets shorted to ground (of course, the device will not retain its clock time when you unplug it if you don't have the backup battery installed).
Note that software versions prior to 1.04 had a bug where the "666" error would not display upon startup, because the high voltage to the tubes had not been turned on yet. With software version 1.03 and earlier, the lack of a clock backup battery (or a dead battery) will result in a blank display when power is connected. The "666" error will display if the clock reading error occurs after startup in the older software versions.

Care and Feeding of Nixie Tubes

Handle your divergence meter carefully to avoid damaging the nixie tubes. The tips of the nixie tubes, in particular, could be broken if you bang them against something, and that could ruin the tube by allowing air inside the tube (which currently has a low pressure gas inside).

Nixie tubes do not last forever. If a tube fails, a replacement will need to be soldered in place after the old tube is desoldered. I haven't had to do this yet on any of my nixie devices, but it doesn't sound like fun. How long do nixie tubes last? Well, places that sell nixie clocks say that the tubes may typically last 5 years with constant use (although they typically guarantee the tubes for only 30 days). My divergence meter incorporates anti-cathode-poisoning routines to exercise all of the tube digits regularly to help extend tube lifetime. The divergence meter also has the option for you to set a range of hours during the day when the tubes will be turned off (times when you are typically out of the house, for example), which can also extend the lifetime of the tubes.

I have a nixie thermometer that had a tube where just a couple digits were going bad over time (parts of the digits were failing to light up). I found a Web page that talked about how to 'heal' such defects by running higer-than-normal currents through those digits for a while. I tried this out and it worked pretty well. I simply hooked up an external 170V power supply (like the kind we used to build this project) to the anode and problem cathode of the tube using a smaller than normal current-limiting resistor (4.7K instead of 33K). I used tiny clips to connect the wires from the power supply to the short tube leads that stick out through the PC board the tubes are mounted on (that's why I told you not to cut those leads too short, in case you ever need to do this). Basically, you are baking the deposits off of the problem cathode (the nixie tube gets noticeably warm during this process). Normally you don't want to run the tube cathodes with high currents because this causes some of the cathode material to bake off and get deposited on the inside of the glass tube, and this will cause the tube to darken over time. But if you can heal the problem digits this way at the expense of a little tube darkening, it certainly beats replacing the whole tube.

QUESTION? Ask me:

--"Tom Titor" of /a/
tomtitor@mindspring.com