EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: BHyman on May 31, 2021, 07:55:57 pm
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Hello everyone
I've been working on a project that is making a clock using IN-14 nixie tubes, 74HC595 shift registers, 74141 nixie tube drivers, a RTC, and an Arduino Nano. I was able to wire up one tube to test some code and get a feel for how they work. I used a 10k resistor (I know the schematic says 68k) with a 170V power supply to power it.
My question is about the decimal point on the tubes. I know on the datasheet it says that the current for it is lower than the normal digits, so I need an additional resistor. Would this resistor go in between the transistor driving that decimal point and the cathode for it, or somewhere else? Do I also need resistors in between the arduino and transistors? Also, how do I figure out the value for the resistors? I've attached a picture of my schematic that I made in KiCAD for this. This is my first attempt at trying to do a project like this and I would really appreciate any advice. Thank you!
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All that is needed is a resistor between the emitter and ground. Connect the base directly to the MCU and the collector directly to the nixie. This is a crude switched current sink. The current will be approximately 4 / R. So a 22k resistor would be approximately 180 microamps.
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Thanks for the quick and detailed response. If you don't mind me asking, where does the 4 in the calculation come from?
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Thanks for the quick and detailed response. If you don't mind me asking, where does the 4 in the calculation come from?
I interpreted it as 5V - 0.7V Vbe drop which gives about 4V.
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I used a 10k resistor for the digits and a 22k resistor for the decimal points.
I would consider multiplexing the digits. You will need far fewer signals. I did a very similar project
http://www.github.com/profdc9/NixieClock (http://www.github.com/profdc9/NixieClock)
where I multiplexed the digits.