Nixie i2c Driver

This simple, custom nixie driver is indented to drive any kind of nixie tubes via i2c interface. It allows to address two tubes with each i2c slave. The module is intended to be stackable and dynamically addressable using dip switches.

• Supports up to 8 stacked drivers
• Each driver module can power 2 nixie tubes

The driver module has been tested with the following nixie tubes:

• IN-4
• IN-7

BOM - Bill of Materials

Name	Count	Component	Description
74141	2x	SN74141 or K155ID1	BCD decoder
PCF8574	1x	PCF8574	i2c I/O expander
SW1/SW2	1x	DIP Switch 4
R1, R2	2x	10kΩ Resistor	bus pull-up
R3, R4, R5, R8	4x	10kΩ Resistor
R6, R7	2x	10kΩ 2W Resistor
C2, C3, C4	3x	0.1µF Capacitor	optional
STACK PWR	1x	pin-2 Male/female pin header	use male header with long pins to stack the module. Use a short pinned header for the bottom module
HV PWR	1x	pin-2 Male/female pin header	use male header with long pins to stack the module. Use a short pinned header for the bottom module
PWR	1x	screw terminal	optional, power can also be supplied via STACK PWR
I2C	1x	pin-2 Male/female pin header	i2c bus, 1:SDA 2:SCL
NX1, NX2	2x	pin-8 Male pin header	90° angle for stackable module
ANODE	1x	pin-6 Male pin header	90° angle for stackable module

Schema

Assembly instructions

• The capacitors are optional as they're used as bypass

Problem Solving

• If the tubes don't light up correctly you might have to change R6, R7. You can use this calculator to determine the resistor values based on the HV power supply

I2c Interface Definition

Byte	7(MSB)	6	5	4	3	2	1	0(LSB)
i2c slave address	L	H	H	H	A2	A1	A0	R/W
I/O data bus	P7	P6	P5	P4	P3	P2	P1	P0

Address Reference

• Only the write addresses are shown as the nixie driver module doesn't support read operations.
• Arduino uses 7-bit addresses, the LSB (R/W) is not set and the address range starts at 0x38

A2	A1	A0	i2c bus 8-bit slave address
L	L	L	0x70
L	L	H	0x72
L	H	L	0x74
L	H	H	0x76
H	L	L	0x78
H	L	H	0x7A
H	H	L	0x7C
H	H	H	0x7E

BCD Decoder Reference

The two bcd decoders each use 4-bit of the 8-bit I/O expander.

The 74141 decoder has 4 inputs marked A,B,C,D which trigger corresponding outputs.

Truth Table

D	C	B	A	Output
L	L	L	L	0
L	L	L	H	1
L	L	H	L	2
L	L	H	H	3
L	H	L	L	4
L	H	L	H	5
L	H	H	L	6
L	H	H	H	7
H	L	L	L	8
H	L	L	H	9

All values above 0x9 are out of range and turn all outputs off.

• "on" range: 0x0..0x9
• "off" range: 0xA..0xF

Using the Nixie i2c module

Based on the logic tables of the bcd decoders, writing to the i2c bus to output numbers is quite simple.

One byte defines the values for both decoders:

Decoder	Bits
NIXIE 1	0000ABCD
NIXIE 2	ABCD0000

Data Examples

Example value	Nixie Output
0xFF	all off
0x12	"21"
0x01	"10"