SMD Nixie Clock

In this lab, students build a functional six-digit digital clock using vintage Russian IN-14 Nixie tubes and modern surface-mount electronics. The project centers on an ATmega328P microcontroller that interfaces with a DS3231 real-time clock via I2C and drives high-voltage shift registers to control the cold-cathode displays. Participants learn to manage mixed-voltage systems, as the device requires an external boost converter to step 12V DC up to the 170V needed for the neon indicators. The assembly process provides hands-on experience with both through-hole components and fine-pitch surface-mount devices, while the software portion introduces embedded firmware development in C using the Microchip Studio environment and ISP programming.

Electronics Surface Mount Device SMD Nixie Tube Cold Cathode Display Microcontroller ATmega328P High Voltage PCB Assembly Soldering Real Time Clock RTC I2C Shift Register Embedded C AVR Digital Clock Microchip Studio ISP Programming Boost Converter

Uploaded by demo on 2026-07-09 · ready · Electronics · Original source ↗

Files: directions.md · PCB.zip · nixie-clock-code.zip

Readiness checks

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Latest report — 2026-07-09 02:45

Readiness: SMD Nixie Clock

Verdict: Ready with caveats · 2026-07-09 · est. parts cost $185–$220

The hardware is largely obtainable, but the project relies on vintage Soviet-era Nixie tubes and indicator lamps sourced from secondary markets. Sourcing these requires verifying "new-old-stock" status. Additionally, the high-voltage shift registers (HV5622) show tightening stock levels at major distributors, which may constrain large group implementations. This is a baseline cold check of current market availability.

Action required

Part Problem Recommended action
MC78L05ABPX Obsolete Use substitute L78L05ACZTR.
67996-103HLF Specific P/N unavailable Use generic 1x3 0.1" (2.54mm) pin header or snap from a larger strip.
IN-14 Nixie Tube Vintage/No longer produced Purchase from secondary market (eBay/specialist) and verify tested status.

Parts

Integrated Circuits and Semiconductors

Part Spec/Package Status Stock Price Source
IC1: ATmega328P-AU LQFP-32 Active 10,288 $2.66 DigiKey
U2, U3: HV5622PG-G LQFP-44 Active 96 $8.81 DigiKey
U1: DS3231SN# SO-16-W Active 3,220 $17.49 DigiKey
U4: 78L05 Regulator TO-92 Obsolete 0 — —

Display Components

Part Spec/Package Status Stock Price Source
N1-N7: IN-14 Nixie Tube Russian Base Surplus Various $20.00 eBay
N4, N8: IN-3 Indicator 2-lead Neon Surplus High $1.75 (3-pk) Electronic Goldmine

Resistors

Part Spec/Package Status Stock Price Source
27 kΩ (R1, R4, R5, R6, R9, R10) TH 5mm Spacing Active 77,612 $0.10 DigiKey
120 kΩ (R2, R7) TH 5mm Spacing Active 35,646 $0.10 DigiKey
4.7 kΩ (R3, R8) TH 5mm Spacing Active 95,094 $0.10 DigiKey
10 kΩ (R11) TH 5mm Spacing Active 619,610 $0.10 DigiKey

Capacitors

Part Spec/Package Status Stock Price Source
0.1 µF (C1, C4, C5) TH 2.5mm Spacing Active 35,451 $0.27 DigiKey
22 pF (C2, C3) TH 2.5mm Spacing Active 390 $0.37 DigiKey

Electromechanical and Support Hardware

Part Spec/Package Status Stock Price Source
Y1: Crystal Oscillator HC49-U (16 MHz) Active 5,201 $0.28 DigiKey
SW1-SW3: Tactile Button RA SPST Ready High $0.60 SparkFun
CON1: DC Barrel Jack TH PJ-102AH Active 35,252 $0.72 DigiKey
BT1: CR2032 Holder SMD/TH Hybrid Active 14,260 $0.38 DigiKey
P1: ISP Header 2x03 2.54mm Active 11,260 $0.56 DigiKey
P2: Power Header 1x03 2.54mm Not in stock 0 — —
Nixie Sockets Machine Tooled Ready High $2.00 Pololu
Boost Converter NCH6100HV Ready High $11.58 eBay
Power Adapter 12V 1A DC Ready High $6.49 Waveshare
Chassis Hardware 4-40 Screw/Nut not checked — — —

Substitutes

For part Substitute Differences Judgment
MC78L05ABPX L78L05ACZTR Physical and electrical match (5V, 100mA, TO-92). Acceptable.

Verify any substitute against its datasheet before ordering.

Other dependencies

  • IDE: Microchip Studio (Active/Ready).
  • Compiler: AVR-GCC (Active/Ready).
  • External Libraries: millis and ds_rtc_lib (Included in source/Ready).
  • Programming Hardware: AVRISP mkII or similar ISP programmer (not checked).
  • Fabrication: 2-layer PCB, 101.60mm x 38.10mm (Ready).
  • Chassis: Wood or 3D printed enclosure (not checked).

Watch list

  • HV5622PG-G: Stock is limited (under 100 units at DigiKey). Monitor availability closely if planning multiple kits.
  • IN-14 Tubes: As vintage stock, prices fluctuate and availability decreases over time. Verify tube testing results from sellers.
  • 22 pF Capacitors: Stock level for specified P/N is relatively low (390 units); easily replaced by generic equivalents if depleted.
Snapshot What the lab depended on when it was uploaded — the baseline the readiness checks research against.

This snapshot describes the hardware and software requirements for the SMD Nixie Clock. This project builds a 6-digit Nixie tube clock (using Russian IN-14 tubes and IN-3 indicators) controlled by an ATmega328P microcontroller and high-voltage shift registers. It relies on a specific external high-voltage boost converter module and vintage cold-cathode display components that are no longer in production.

Bill of Materials

The following list is derived from the KiCad PCB design (nixie.kicad_pcb), the schematic, and the assembly directions. Where discrepancies exist (notably resistor values for the indicators), they are highlighted.

Integrated Circuits and Semiconductors

  • IC1: ATmega328P-AU
    • Quantity: 1
    • Package: LQFP-32 (7x7mm, 0.8mm pitch)
    • Function: Main microcontroller.
    • Sourcing Plan: distributor lookup: ATMEGA328P-AU
  • U2, U3: HV5622 High Voltage Shift Register
    • Quantity: 2
    • Package: LQFP-44 (10x10mm, 0.8mm pitch)
    • Electrical Constraints: 32-channel, 220 V open-drain outputs.
    • Note: Assembly docs suggest the physical legs may be longer than the footprint; trimming may be required.
    • Sourcing Plan: distributor lookup: HV5622PG-G
  • U1: DS3231N Real Time Clock
    • Quantity: 1
    • Package: SO-16-W (Wide body SMD)
    • Electrical Constraints: I2C interface, integrated temperature-compensated crystal oscillator.
    • Sourcing Plan: distributor lookup: DS3231SN#
  • U4: 78L05 Voltage Regulator
    • Quantity: 1
    • Package: TO-92 (Through-hole)
    • Electrical Constraints: 5 V output, 100 mA.
    • Sourcing Plan: distributor lookup: MC78L05ABPX

Display Components

  • N1, N2, N3, N5, N6, N7: IN-14 Nixie Tube
    • Quantity: 6
    • Package: Russian nixie base (wired leads).
    • Electrical Constraints: Strike voltage approx. 170 V.
    • Sourcing Plan: retail shopping search: IN-14 Nixie Tube
  • N4, N8: IN-3 Nixie Indicator Lamp
    • Quantity: 2
    • Package: 2-lead neon bulb.
    • Electrical Constraints: Used as decimal/colon separators. Note polarity: arrow at base points from positive to negative.
    • Sourcing Plan: retail shopping search: IN-3 Neon Glow Lamp

Resistors (Through-hole, Vertical Mount, 5mm Lead Spacing)

  • 27 kΩ Resistors (R1, R4, R5, R6, R9, R10)
    • Quantity: 6
    • Function: Current limiting for IN-14 tubes.
    • Sourcing Plan: distributor lookup (representative example): CF14JT27K0
  • 120 kΩ Resistors (R2, R7)
    • Quantity: 2
    • Function: Current limiting for IN-3 lamps.
    • Discrepancy: The board file (.kicad_pcb) labels these as 100 kΩ, but the assembly directions and project text explicitly specify 120 kΩ to protect the smaller lamps. Use 120 kΩ.
    • Sourcing Plan: distributor lookup (representative example): CF14JT120K
  • 4.7 kΩ Resistors (R3, R8)
    • Quantity: 2
    • Function: I2C Pull-ups for DS3231.
    • Sourcing Plan: distributor lookup (representative example): CF14JT4K70
  • 10 kΩ Resistor (R11)
    • Quantity: 1
    • Function: Reset pin pull-up for ATmega328P.
    • Sourcing Plan: distributor lookup (representative example): CF14JT10K0

Capacitors (Through-hole, Disc, 2.5mm Lead Spacing)

  • 0.1 µF Capacitors (C1, C4, C5)
    • Quantity: 3
    • Electrical Constraints: Voltage rating ≥ 10 V.
    • Sourcing Plan: distributor lookup (representative example): K104K15X7RF53L2
  • 22 pF Capacitors (C2, C3)
    • Quantity: 2
    • Function: Crystal load capacitors.
    • Sourcing Plan: distributor lookup (representative example): CC45SL3AD220JYNNA

Electromechanical and Support Hardware

  • Y1: Crystal Oscillator
    • Quantity: 1
    • Package: HC49-U Vertical.
    • Note: While value is not in BOM, standard ATmega328P clocking is 16 MHz.
    • Sourcing Plan: distributor lookup (representative example): ATS16B
  • SW1, SW2, SW3: Tactile Push Buttons
    • Quantity: 3
    • Package: Right-angle SPST tactile switch, through-hole.
    • Sourcing Plan: retail shopping search: Right angle 2-pin tactile push button
  • CON1: DC Barrel Jack
    • Quantity: 1
    • Package: Through-hole barrel jack connector.
    • Sourcing Plan: distributor lookup (representative example): PJ-102AH
  • BT1: CR2032 Battery Holder
    • Quantity: 1
    • Package: nixie:CR2032 (SMD/Through-hole hybrid).
    • Sourcing Plan: distributor lookup: BAT-HLD-001
  • P1: ISP Header
    • Quantity: 1
    • Package: 2x03 (6-pin) straight male header, 2.54mm pitch.
    • Sourcing Plan: distributor lookup: 67996-206HLF
  • P2: Power Interface Header
    • Quantity: 1
    • Package: 1x03 (3-pin) straight male header, 2.54mm pitch.
    • Sourcing Plan: distributor lookup: 67996-103HLF
  • Nixie Sockets (Machine-tooled Female Headers)
    • Quantity: 60 pins (Extracted from 1x40 or 1x50 strips).
    • Function: Individual pins are extracted from the plastic carrier and soldered into the board to act as sockets for the IN-14 tubes.
    • Sourcing Plan: retail shopping search: machine tooled female header strip 2.54mm
  • High Voltage Boost Converter Module (External)
    • Quantity: 1
    • Identity: NCH6100HV High Voltage DC Power Supply.
    • Function: Converts 12 V DC to 160-170 V DC for the tubes.
    • Sourcing Plan: retail shopping search: NCH6100HV Nixie Power Supply
  • Power Adapter
    • Quantity: 1
    • Identity: 12 V DC Wall Adapter with Barrel Jack.
    • Sourcing Plan: retail shopping search: 12V 1A DC power supply barrel jack
  • Chassis Hardware
    • 4x 4-40 Screws and 4x 4-40 Nuts for PCB mounting.
    • Enclosure (Wood or custom 3D printed/CNC machined).

Firmware and Software

The firmware is developed in C and depends on specific toolchains and libraries that may become deprecated.

  • IDE: Atmel Studio (now Microchip Studio). The project file is NixieCode.atsln (Visual Studio 2010 based shell).
  • Compiler: AVR-GCC (contained within Atmel/Microchip Studio).
  • External Libraries:
    • Zak Kemble's millis library (included in source).
    • Akafugu's ds_rtc_lib (included in source).
  • Programming Hardware: Requires an AVRISP mkII or similar ISP programmer to interface with header P1.

Fabrication Details

  • PCB Dimensions: 101.60mm x 38.10mm (4" x 1.5").
  • Layers: 2 layers (Top and Bottom Copper).
  • Design Files: KiCad format.
  • Constraint Note: The PCB width is matched to the NCH6100HV power supply module for stacked or side-by-side mounting in an enclosure. Use of the provided Gerber files is recommended to ensure footprint compatibility for the vintage Nixie tubes.