Nixie IN-1 Clock

Nixie IN-1 Clock
A 6 digit Nixie clock.

Features:

(6) IN-1 Nixie Tubes with Sockets
(5) INS-1 Nixie Bulbs
Nixie Lifespan Maximization
GPS Disciplined Primary Timebase
Accuracy: ±1 Second
Automatic Time Setting
Single Rotary Encoder Interface
Motion Sensor
12V 1A Power
3D Printed Enclosure
Modular Design

Design Documents

Schematic Diagram - Controller Board	nixie_IN1_schematic.pdf
Schematic Diagram - Backpack Board V1	Nixie Backpack I Schematic.pdf
Schematic Diagram - Backpack Board V2	Nixie Backpack II Schematic.pdf
3D Print Files	nixie_IN1_mechanical.zip
Source Code - Arduino (clock controller)	Arduino.zip
Source Code - PIC12F1822 (backpack V1)	pic12f1822.asm
Source Code - PIC16F1615 (backpack V2)	pic16f1615.asm

Operation

Power Supply	Requires 12V 1A DC
Power Bulb	Always on
Digit Tubes	Auto shutoff after 30 minutes of no motion
Punctuation Bulbs	On with Digit Tubes when GPS time signal is locked on
Knob Turn	Test digits, automatically returns to time display
Knob Press	Turn knob to change the UTC to local time offset

Dual IN-1 Backpack
The clock is built using three Dual IN-1 Backpack modules and a main controller board. Each Dual IN-1 Backpack has a microcontroller and the drive circuitry for two IN-1 tubes. The backpack is supplied with +5V, +170V, and controlled via a serial interface. The serial interface is 9600 baud receive only, and all the backpacks are connected in parallel.

There are two versions of the Dual IN-1 Backpack.

The first version uses a Microchip HV5622 and PIC12F1822. The HV5622 is a high voltage shift register with latch, which works great because the outputs all change simultaneously. This makes the software easy. The HV5622 chip is rated for 12V and can switch high currents; however it was found to work at 5V as long as it's switching low currents, which is enough for the Nixie tubes. It won't quite work at a lower voltage; it starts dropping out right at 3.3V. This design also includes some anode switches (Q1 and Q2), which are not really needed, so they have been bypassed. However HV5622 is an expensive chip and a little difficult to solder, so the design could be improved.

Code for this design

The second version uses a Microchip PIC16F1615 and discrete transistors. This design cheaper and easier to solder by hand. Plus it operates at 5V or 3.3V The design lacks the latch capability, but this makes no practical difference in the display performance.

Code for this design

Each backpack is assigned an ID from A to Z. In this clock the backpacks are designated 'H', 'M', and 'S'. The backpack ID is set by connecting one backpack at a time and issuing the special command ATID=X, where 'X' is the ID (A to Z). The ID is stored permanently in the backpack.

Backpack display commands consist of 3 characters; the ID followed by two digit values. If the ID is lowercase then a fade is performed (a cross fade from the current number to the next). Special ID characters '@' (immediate) and '*' (fade) address all backpacks.
Examples:
    @--    (blank both digits in all modules instantly)
    H12    (set module 'H' to '12', instant)
    h12    (set module 'H' to '12', with fade)
    H12M34S56    (show "12:34:56" instantly)

The tube "sockets" are rather disappointing. Modified Molex (02-09-1102/4) connectors are used as tube pin sockets. They are a little too small so some rework is needed to make them fit. Plus they aren't designed to be tube sockets in the first place, so it's impossible to make them fit really well. But they do barely work and the tubes are removable.

5V Backpack Nixie Power Supply*
The Dual IN-1 Backpack normally requires a high voltage power input for the Nixie tube. To run from 5V, this piggyback power supply can be used; it produces about 185V at 5mA, which is enough for two IN-1 tubes.

This makes a 5V-only dual IN-1 module.

The voltage regulation is not great. This is how it performs at various load levels...

vIn	mAin	Vout	mAout	Efficiency
5.0	20	210	0.0	No load
5.0	150	188	3.0	75%
5.0	260	186	5.4	77%
5.0	420	182	8.9	77%

Bill of Materials

Part ID	Quantity	Description	Size	Part	Source
C1,C4,C5	3	1uF 100V capacitor	1206	100VDC 1uF 20%	Mouser 963-HMK316BJ105ML-T
C2	1	100uF 6.3V capacitor	1206	6.3VDC 100uF	Mouser 963-JMK316ABJ107ML-T
C3	1	47pF 100V capacitor	0805	47pF 0805 5%	Mouser 710-885012007080
D1,D2,D3	3	100V fast diode	SOT-23	BAS16	Mouser 771-BAS16-T/R
D4	1	91V Zener diode	SOT-23	91V 225mW	Mouser 863-MMBZ5270BLT1G
L1	1	100uH inducor	8mm	100uH 20% 1.1A	Mouser 652-SRN8040TA-101M
Q1	1	NPN transistor	SOT-23	NSV1C201LT1G	Mouser 863-NSV1C201LT1G
Q2	1	NPN transistor	SOT-23	PMBT2222A	Mouser 771-PMBT2222A-T/R
R1	1	750 Ohm resistor	0805	750 Ohm 1%	Generic
R2	1	22K resistor	0805	22K Ohm 1%	Generic
R3,R4	2	100K Ohm resistor	0805	100K Ohm 1%	Generic

Printed circuit board
PCB
PCB Gerber files for this board

* Credit for the original circuit design goes to The LED Artist.

This clock needs high voltage for 3 dual backpack modules, punctuation bulbs, and a power indicator bulb, so a single high voltage module that can provide at least 20mA at 170V is used.

Clock Controller Board
The controller PCB has the Arduino Pro Mini and a bunch of connectors to plug in all the modules.

Arduino code for the clock

Nixie Time Display
This clock doesn't have a typical AM/PM indicator. AM/PM is indicated by alternating 12 and 24 hour time formats every 2 seconds.

The clock punctuation is four INS-1 bulbs, which are normally on when the clock is on. If the punctuation is off that means the GPS signal is not locked on.

The power indicator is one INS-1 bulb, which is always on.

Auto-Shutoff occurs after 30 minutes of no motion detection. All Nixies except the power indicator are shut down. Cathode de-poisoning is performed just prior to shutdown.

Automatic cathode de-poisoning is performed every hour of continuous operation. The display will flash for a few seconds during this process.

User Interface
The user interface is a rotary encoder with push.

Turn the knob to test the display; it simply turns on all the same digit.
Press to enter time setting mode, turning the knob adjusts the UTC offset.

Motion Sensor Module
A small PIR motion sensor activates the clock.

Time Base Module
A NEO-6M GPS module provides the primary time base. The processor takes over timekeeping during periods when the GPS signal drops out.

High Voltage Power Supply Module
A generic MAX1771 based high voltage module makes 170V for the Nixies. This tiny module makes just enough current, ~20mA for the clock.