In the TIME mode, press and hold the "Set Hour" button. You can find the piece of program for this purpose in the internet.) (If you want the temperature is displayed in Fahrenheit degrees, you should change the program of Arduino accordingly. ![]() The other digits remain OFF in the thermometer mode. As the digit are assembled in groups of two, there is no need for a decimal point. To middle tubes will show the degrees and next tube on the right shows one-tenth of degree. In this mode, the ambient temperature is displayed in Celsius degrees. This button also acts for start/stop of the timer.ģ) THERMOMETER mode: The thermometer mode can be selected by the selector switch. In the TIME mode, date can be displayed by pushing the "Date" button.Ģ) TIMER mode: If the selector switch is in TIMER mode, you should first push the “Date” button to reset the timer. If nobody is present (and moves) in front of the clock, the lamps will be shut down after about 2 minutes, to lengthen the life of the tubes.īy turning the SW1 switch on, you can bypass the PIR sensor so that the tubes will remain ON permanently. You can tilt the tubes to have a good angle of view.ġ) TIME mode: In the normal operation, time is displayed. Try to align the tubes on board carefully to have a nice look. I installed the nixie tubes in three groups of two (for hours, minutes, and seconds), so there was no need to add a separator lamp. When the tubes proved to work correctly, you can proceed to add RTC module, LM35 temperature sensor, the PIR sensor, and the switches, push buttons etc. You can find proper instructions in the internet.Ĩ) Connect the Arduino. (+180 V with a 22k resistor in series to the anode, ground the the other pins on by one)ģ) Connect the similar pins of the tubes together (except the anodes) for multiplexing.Ĥ) Test the wiring by applying high voltage to each anode and cathode.ĥ) Assemble of the high voltage transistors and the 74141 IC.Ħ) Test the circuit by applying high or low logic levels (0 and +5v) to the inputs of 74141 and base of the MPSA42 transistors, each digit of the corresponding tube should glow.Īs you may know, the Arduino pro mini needs a special interface to be connected to computer. The high voltage generator uses a 555 oscillator and a MOSFET transistor.ġ) Assemble the high voltage circuit and adjust the voltage at 170-180 Volts by the potentiometer.Ģ) Test the nixie tubes and find their pinout. So I added a monostable multivibrator (CD4098) to lengthen the time delay. The PIR modules that have adjustable time delay, are bigger and do not fit in my compact design. ![]() I preferred this time to be around 2-3 minutes. Unfortunately, this module holds the output signal for only 8 seconds, which is not enough in my opinion. It will hold the time and date very precisely over a long time, maybe more than 1 year.įor the PIR sensor, I used a tiny module (SR505). To hold the time in case of power disconnection, I used an RTC module (real time clock) that utilizes a 3V lithium battery. In order to drive the anodes, I used two high voltage transistors per digit (obviously the Arduino cannot handle 180 volts!) One 74141 in enough, because the tubes are multiplexed. The 74141 (or 7441) IC is a BCD-to-decimal convertor that is able to handle high voltage. The nixie tubes are multiplexed, to reduce the pins required for operation of 6 digits. Besides, I could not find the footprint of the nixie tubes. I did not design a PCB, because I intended to make a prototype. Write down the pin number and the corresponding digit that is displayed. The common pin, (Anode) should be connected to +180 v and each of the other pins is connected to ground, via a 2.2K resistor. You can find the pinout by searching the tube number in the internet, or you can find the pins by applying 180 volt DC to the pins. You can use any nixie tubes that you can find, and the electrical specifications are pertly similar. In my case, the metallic pins were severely corroded and some of them were detached from the connection point to the glass! I soldered a wire to the point, and fixed it by cyano-acrylate (1,2,3) glue. In most cases, the display of a calculator is not the part that is damaged :) I scavenged 12 nice Nixies from an old calculator that was not working. Although they are still available in the online stores like ebay etc. They look very beautiful, but unfortunately, they are hard to find these days. They are essentially neon vacuum tubes and each digit is a cathode of the tube, which glows upon high voltage connection. Nixie tubes were standard display for numbers, before invention of seven segments.
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