The Embedded Electronics

After the breadboard prototyping, I made a single Nixie Tube Output Device. With the experience I made, I started to design the board in a similar way.

I made also two pluggable circuit boards: One for the tubes and one for the controller.

So in that way, it would be possible to change the controller circuit in the future, if needed.

In my breadboard prototyping state, I tried some different ways getting the time. In the end I used the DS1307 module after all.
Everything else, seems to be unpractical.

Routing the traces was a real brain performance training :-D
Other people play sudoku and I was routing traces for days, with the goal of less bridges as possible and placing the pinheaders and sockets, that they fit together.

KiCad

As in my assignments, I used KiCad for building the electronics.

It was a game between drawing the schematics and routing the traces. When I saw, I need to bridge a trace, then I’ve added a 0 Ohm resistor in the schematics.
And so that no boredom arises, I used other pin-mappings between the 74HC595 and the K155iD1 and also between the K155iD1 and the tubes.
That makes the logic tables obsolete and I have to “correct” it, in the program code.

At the end, the schematics looks like this…

For the pcb design, I’ve added some ‘orientation’ lines.
Here is a picture of an more or less early state…

This is a more advanced state…

And here is now the finished board layout…

But I made a mistake here. The 4 pin pinheader on the top of the top-board, is to far to the left and it doesn’t fit in it’s socket on the controller board.
Because of that, the 4 dots wouldn’t be able to turn on and off with the microcontroller.
I saw this during the assembly and have fixed it involuntarily with wires. More about that in the soldering section.

On the bottom pcb are two green ‘backside’ traces. I used this, to route the VCC line with wires on the backside of the pcb. This allowed me to save a few 0-Ohm bridges.

BOM

The hole circuit needs the following parts:

1x 12V Power Supply
1x NCH6100HV (HighVoltage StepUp Module)
1x DS1307 RTC Module
6x ZM1042-B13B
4x IN-3
78x d-sub pin female (optional as Tube Socket)
6x 74141DIP16 or K155iD1
4x MMBTA42
3x 74HC595 (SMD)
1x AMS1117-5.0
1x ATmega328-AU
1x Barrel_Jack (internal or external
1x 1uF (0805)
1x 100nf (0805)
6x 6K8 2W (THT)
4x 180K 1W (THT)
1x 10K (0805) 

1x PinHeader 01x07 Vertical SMD (for RTC DS1307)
1x PinHeader 01x06_Male Horizontal SMD (for FTDI)
6x PinHeader 02x05 Vertical SMD
6x PinSocket 02x05 Vertical SMD
1x PinSocket 02x02 Vertical SMD
1x PinHeader 02x02 Vertical SMD

1x PinHeader 01x02 Horizontal SMD for 12V Output 
   (Optional - wires can soldered directly to the board)

For Bridging there are: 

12x 0R Resistor pads
4x Via

For Optional Functions:

1x PinHeader 01x05 Vertical SMD
5x TestPoint
1x PinHeader 01x04 Vertical_SMD (for internal RX/TX)

Additional Information

I’ve found some projects where MMBTA42 transistors where used for the tubes.
I decided to use them to control my dots. With them I’m able turn the dots on and off with the ATmega328.

Instead of the ATmega328 it is also possible to use e.G. an ATmega324 (or 644). The ATmega324 has more output pins and because of that, the circuit could made without the 74HC595 shift register.
I’ve tried to build a circuit with the 324, but the routing was to complex, more bridges would be needed and also a bigger pcb.

Here is a screenshot of my try…

Downloads

The complete KiCad archive can be downloaded HERE
It contains the gerber and flatcam files, too.