Base module provides power, user interface and connectors for both logic and display modules. This creates base for entire device.
Power is delivered througt DC jack. It uses 12VDC. As it is safer to use stabilized power source in fact this voltage may be unstabilized – everything between 10V and 15V should work fine. Module generates voltages for powering display, logic and some of user interface. Single glass fuse is implemented for short circuit protection.
High voltage for Nixie tubes is generated by step-up converter. It is based on MC34063 chip. Voltage of about 170V is generated. It can be precisely adjusted by RV1 potentiometer. Depending on power consumption by display – Q1 transistor may require a heatsink. Such design of step-up converter is commonly used in this kind of clocks.
Module generates also 5V for logic. It may be done in 3 ways. U3 is a footprint for standard 78M05 linear regulator that provides 5V. For higher power consuming logic, instead of linear regulator, step-down converter use is recommended, and it is to be installed in Module 1 footprint. This footprint is compatibile with widely available ready made step-down power converter modules. This footprint is also compatibile with 78L05 regulator in TO-92 case, which makes it third option for providing power for logic module. As heat disspation capabilities are limited for this kind of case only low power logic modules can be powered this way. When using linear regulator or power convetring module, other footprint remains unpopulated.
The input voltage can be also directly connected to J5 connector. This was originally designed for testing and prototyping. When using it notice that is bypasses fuse, so extra care should be taken.
Base module provides also an interface for user. Input devices available in this design are buttons and integrated infrared receivers, if clock shall be set by remote control. Output devices are LEDs which can be used for signalling or just creating some fancy light effects. Base modules also holds place for hour minutes separator.
Module provides three footprints for push buttons. Buttons are described on silkscreen with symbols showing up and down arrows and circle for „enter”. Buttons connect their leads to GND. Resistors R11 to R13 are pull-ups for respective buttons to V-logic. V-logic is voltage provided by Logic Module and it powers its circuits. When Logic Module contains its own regulator (for example 3.3V) – V-logic is output of this regulator. When logic is powered directly from 5V – V-logic has to be connected to 5V on Logic Module.
Instead of up button – integrated IR receiver of TSOP44xx/TSOP48xx series can be installed. Receiver is also powered from V-logic, so its output levels are compatibile with logic circuits. As receivers can operate in wide range of voltages (2.5-5.5V) they become universal and easy to use with large variety of Logic Module solutions.
As mentioned before – some LEDs can be intsalled on the module. These are D3, D4, D5, and D6 – 3528 LEDs. They are connected into two parallel circuits – two in series with resistor (R9 and R10). Each circuit is powered from main 12V power. Both circuits are driven together by logic module with transistor Q3 (BC-817) – which would be standard small signal NPN transistor. Base current is set by R8 (10k – 30k should be fine).
Module also provides place for minutes hours separator. This can be either neon bulb or LED. Resistor R18 sets current for separator and jumper J1 selects power source. Position 1-2 selects 5V (used for LED), position 2-3 selects hihg voltage from step-up converter (for neon bulb).
Module also provides interconnections. One is for Logic Module and other is for Display Module. More detailed description is provided in repective sections of each module.