Introduction:
This is the hardware and source code for an Atmel ATmega48 based four digit Nixie Tube Clock.
Description:
This was my second Nixie clock project. I wanted something a little smaller / cheaper / simpler then my rather large B-7971 clock. I will post the design for that one of these days. I was trying to simplify everything. And basically wound up with a one chip solution, … the micro itself does just about everything.
The Nixie tubes are relatively cheap and available (Ebay) Russian IN-17s.
Discrete transistors drive the tubes in a 1×4 mux arrangement. Needs 15 I/O lines from the processor.
No external RTC chip. Saw no need for 10 years backup with a lithium battery. Really just wanted a few hours to handle the typical short term power outages I get so I don’t have to reset the time too often. The mega48 has some very low power operations and support for an asynchronous xtal clock that’s perfect for RTC functions. This alone makes the newer Atmels more attractive for clock designs. A relatively small ‘supercap’ provides back up power during mains outages (8-12 hours).
The high voltage is generated with an fet and inductor connected to one of the PWM outputs on the chip. The voltage is measured via one of the A/D channels, and the PWM value is adjusted to provide regulation. The voltage van be adjusted via push buttons during set up and the value is stored in non-volatile memory (no voltage adjustment pot)
No alarm / speaker / temperature / Westminster chimes on this design, I wanted simple.
Two push buttons provide a user interface to set time and options.
A simple extruded aluminum case finishes the design.
Construction Notes:
I designed two seperate PCBs for the clock. One for the IN-17 display, other one for the Atmel and everything else. It’s a mixed TH / SMD single sided design with just a few jumpers. I used toner transfer to make the boards and I don’t have any extras. If people are interested, I can provide artwork. The traces on the display boards are a little on the fine side and it was a little tricky to fabricate. I used all smd transistors for the HV drivers and some pretty small resistor networks to get everything to fit the way I wanted. A lot of the parts were surplus items I had laying around the shop, so I really don’t have a detailed BOM with digikey numbers for everything. Nothing is too critical and you can make substitutions.
Read more: Nixie Clock with AVR using ATmega48 microcontroller