Nixietube Wristwatch

Last year I got inspired by Nixitube clocks. I think the looks of the Nixietubes are so nice. I thought about implementing this in a stylish watch with smart functionalities.

I started by creating the electronic schematics for a four tube watch. Being an electronics student I developed the electronics over a several months.

First a power supply has to be designed. I started off by buying an premade 170V switch mode power supply from the web because I did not know how to design a power supply which could convert 4.2V DC from a battery into 170V DC for the tubes. The pre made PSU was 86% efficient.

After receiving the power-supply I started researching how to control the Nixietubes. The Nixietubes I got where common Anode tubes which means that when you put 170V DC on the Anode and GND on the cathode the tube will glow. To limit the current flowing trough the tube a resistor has to be placed in front of the anode. Causing the current to be limited to 1mA per tube. To control the different digits. I used high voltage shift registers. These IC's can be controlled by any micro-controller.

Since I am a big fan of IoT (Internet of Things). I decided to take an ESP32 module and wanted to get the current time from the internet though WiFi. Eventually I was synchronizing an RTC (real time clock) with the internet time. Allowing me to save energy and always have the time at hand even without internet access.

I Thought about ways to check the time and came up with using a Accelerometer which I used to track the movement of my wrist. When I turn my wrist so I can read the time. The watch will trigger and show it to me.

I also implemented three touch activated buttons so I could make a simple menu where I could set different functions.

Two RGB LEDs had to give a nice back glow to the tubes.

I also thought about a way to charge the battery. Therefore I came up with charging it by using a wireless QI charger module. This module gave me 5V output. This module connected to a charging circuit allowed me to charge the small 300 mAh battery.

When the electronic design was ready and all the sub circuits where tested I started designing the PCB (Printed Circuit Board). I was making mock-ups with paper and the parts (picture 1). Measuring the width, height and length of every component was a painstaking process. After weeks of designing and laying out the PCB they got ordered and shipped to me. (picture 2).

During every step of the way I had created test-programs for every part of the watch. This way the final software could easily be copied together.

The soldering of every component could begin and took me about a day.

Testing and putting the whole watch together (Picture 3,4,5,6,7) It worked.

I 3D printed a case for the watch and eventually found the watch to be too big. So i decided to create a new one and made the four tube watch a prototype.

Finding the four tube watch too big I started to shrink the electronics design. First by using only two tubes instead of four. Secondly by using smaller components and making my own 170V boost converter from scratch. Implementing the ESP32 MCU (Micro Controller Unit) myself instead of using a module also made the design much smaller.

Using 3D design computer software (Picture 1) I designed a case and fit all the electrical components neatly inside. By dividing the electronics into three board I was able to more efficiently use the space inside the case.

New electronics where designed:

-Picked a new more power efficient Accelerometer.

-Changed the touch buttons for a multi position switch.

-Used a new charging circuit.

-Changed the wireless charging for USB charging because I wanted an Aluminium housing.

-Used a low power processor to further save power.

-Picked a new background LED.

-Used a battery gauge IC to track the battery level.

After months of designing the new watch it could also be assembled. I used some tools available on my school to solder the Tiny pitched IC's (Picture 4). This took me several days because I ran into some problems but eventually I got the electronics working (Picture 5).

I designed the case in parallel with designing the electronics. Each time checking in a 3D computer software if every component would fit. Before CNC (Computer Numerical Control) milling the case, a 3D printed prototype was made to make sure everything would fit. (Picture 1,2)

After the case design was done and the electronics worked I started research about how CNC machines must be programmed (Picture 3). A friend of mine who has knowledge about CNC milling helped me program the CNC machine. So the milling could begin. (Picture 4)

After the milling was complete i finished the case by drilling holes and polishing the case. Everything fitted the first time right. (Picture 5,6,7)

I had designed a latch for an acrylic window. But the latch was milled away by accident. Using a laser cutter I cut a window from acrylic this was glued to the top of the watch (Picture 9).

The controller on the watch basically sleeps all the time to save power. A low power processor reads the accelerometer every few milliseconds to check if my wrist is turned. Only when it is turned it will wakeup the main processor and get the time from the RTC and will show the hours and then the minutes briefly on the tubes.

The main processor also checks the charging process, it checks for incoming Bluetooth connections, it checks the state of the input button and reacts accordingly.

If the user is not interacting with the watch any further the main processor will go to sleep again.

As part of my study we had to create an app. So I thought creating the app for the nixie watch. The app was written in xamarin from Microsoft language is C#.

I had to create the app in dutch unfortunately. But basically there is a connection tab which shows the found nixie watches (Picture 1). After that the settings from the watch are downloaded. These settings are saved on the watch. A tab to synchronize the time manually or automatically by getting the time from your smartphone (Picture 2). A tab to change settings of the watch (picture 5). And last but not least a status tab which shows the battery status. (Picture 6)

The watch features:

- Two small nixie tubes of type z5900m.

- Accurate real time clock.

- Calculations showed that 350 hours standby time was easily achievable.

- Bluetooth for controlling settings and setting the time of the watch as well as seeing the battery status.

- Some Bluetooth settings include: Animation On/Off, Manual or accelerometer triggering of tubes, background led On/Off. Programmable button for seeing temperature of battery percentage.

- Accelerometer for triggering the tubes when wrist is turned

- 300 mAh battery.

- RGB led for multiple purposes.

- Battery gas gauge IC for accurately monitoring the battery state.

- micro USB for charging the battery.

- One multi direction button for triggering, Bluetooth connection and a programmable button for temperature reading or battery status, Setting the time manually.

- CNC milled housing from Aluminum.

- Acrylic window for protection

- Bluetooth phone application.

- Optional time synchronization via WiFi.

- Optional Vibration motor to indicate smartphone notifications like Whatsapp, Facebook, Snapchat, SMS...

- First the hours then the minutes are shown.

The software for the MCU on the watch is written in C++, C and assembler.

The software for the app is written in xamarin C#.