Vermes
Advanced Member level 4
This construction of a clock is based on Nixie tubes. Although there are many similar constructions on the Internet, only some of them show how exactly build such a clock with the housing. The clock were made of cheap and easily available elements. Indicators are LC516 that are compatible with In-1 and, after some modifications, Z560M.
The assumption of this construction was to create a simple clock without the unnecessary elements such as GPS, DCF, LED, etc. It was to implement the following functions:
- be powered from 12V (plug power supply)
- count down the time in format HH:MM 24h
- blinking second counter 1Hz
- alarm 24h
- possibility to turn out the tubes
- brightness adjustment of the tubes depending on the brightness of environment
- maintain of counting down the time at the moment of power failure
- possibly small size
The clock was modeled in CAD 3D before starting the construction. That allowed to find possible faults and mistakes which can be relatively difficult to be fixed during final assembly of the device.
Electronics consist of two PCBs connected together in “sandwich”. The upper PCB consists of Nixie tubes, and the other components are placed on the bottom PCB.
The clock uses only one chip Atmega16 that implements all the necessary features:
- multiplexed display
- RTC time refresh
- controlling the converter that increases the voltage
- brightness adjustment of the tubes depending on the brightness of environment
- alarm support
- handling the reaction to voltage failure
Electronic schematic is based on standard application of AVR processors, the tubes can be controlled in basis of high-voltage bipolar transistors. An internal quartz resonator was used in this device, and the external crystal quartz is used for clocking the RTC. During writing the RTC procedures you may find useful some Atmel materials: Application note of AVR134: Real Time Clock (RTC) using the Asynchronous Timer.
The converter was made in Boost typology, descriptions of which you can easily find on the Internet. It can be controlled by PWM output. The return information on the output voltage is gained by the processor from the analog input. A hysteresis regulator was implemented for the stabilization of output voltage. The regulator has a significant speed in dynamic states.
Voltage failure of the supply is detected by the interrupt from analog comparator and voltage divider connected to the supply voltage 12V. In a case of power failure, the processor turns out the tubes and switches to energy saving mode, during which it is powered from a super-capacitor 1F/5V what allows to count down the time up to 8 hours. When the voltage is restored, the clock automatically returns to normal work.
Software was written in C, using WinAVR + AVRStudio.
White color of the soldermask presents excellent through the transparent housing.
The design assumed making mechanic components of available and easily processed materials (plexiglass and wood). Treatment was to be carried out with use of CNC equipment.
The mechanics was to be classical one, without the unnecessary lights and frills. The top and bottom boards were made of strips of oak machined on CNC, and then stained to a nice brown color. There is a milling for the non-slip silicone feet on the boards.
The plexiglass was cut using the laser, what gave the glass effect on the edges. The whole was screwed using the M3 spacers.
Link to original thread - Zegar Nixie ElectroNIX Clock