The Dome Clock

The evolution of the Circus Clock:

Also for further reading and to understand the electronics behind the clock please read:

The idea behind the Dome Clock was to build a new one under glass.

To read the clock you have to mention the horizontal and vertical numbers. In the normal mode the clock uses the horizontal digits for the hour and the vertical for the minutes. There are no seconds like in the Circus Clock. But the Dome Clock has also a date mode. In the second 40th to 49th the date is shown but now changed: the months are in vertical and the days in horizontal direction. Monday to Sunday are the neon bulbs from the pendulum in the back. The first from the left side is Monday, on the right Sunday.The pendulum is driven by 7 MPSA42 transistors over a MCP23008.

Power supply of the Dome Clock

The Dome Clock is divided into two parts: the lower part is the power supply. You have to imagine that the different tubes have different needs due to the voltage. In this case we need: 5V for the electronics and the Numitron tube (right), 12V for the DC/DC to produce 24V for the vacuum fluorescent seven segment tube (left), 150V for the Nixie tube (Up) and then 45V, 90V and -270V for driving the thyratron seven segment ITS1A (down) (I love this tube with a real fancy method to glow some phosphor with secondary electrons). For Details of the power supply read:

There is a neon bulb pendulum in the back but to give the clock a more clockish view I build a magnetic pendulum out on an old amp meter. This was build in a tractor with a scale of more than 30A, so I removed the really thick wire and coiled up a new thin isolated copper wire. I test a bit with the numbers of turns to find the right amount for 5V it is driven by a BC547 over a Arduino port. To make it more dramatic we insert a UV Led which illuminates the pendulum in the dark and gives a good contrast to the orange neon bulbs.

The magnetic pendulum in the dark. (And look on the left side! Did you see the pink, redish plasma beam of the thyratron nixie? Ending up in green phosphor fluorescence!)

A realtime clock (DS3232) was connected to an Arduino Nano which controls the whole clock. The main principle was to use port expander like the MCP 23008 and drive them via I2C.

I use four MCP23008 to expand the IOs of the Arduino. One MCP for the neon bulb pendulum (7bit), two CD4511 for the Numitron and the VF seven segment tube driven by a single MCP. So I use the upper and lower four bits for the BCD to 7 seg encoding. The Nixie use a single MCP with a russian K155ID1 (and do not forget a resistor for limiting the current!), and the last MCP with a dircet encoding of the ITS1A with 7 bit for the segments a the last bit for a high voltage opto coupler to switch off the -270V to clear the seven segment. For more Details please read the article about the CIrcus Clock.

Dome Clock in the dark