0
\$\begingroup\$

I have bought a Noritake itron vacuum fluorescent display, to use in an Arduino project. A menu with settings will be shown on the display, and the user can interact with it by using some buttons.

My question is:

When the user does not use the VFD display to change settings and such, should I program the Arduino to turn off the filaments inside the display? Should I leave the display on all the time?

I'm thinking that if I leave the filaments turned on all the time, with the individual segments not lit, I will get sputtering, and that's undesirable. Also, if I leave the display fully on (both filaments and individual segments) then in time, I will get either burn-in or fading of the phosphorus on the individual segments. I have it currently set that if the user doesn't interact with it for 10 seconds, then the whole display shuts off, including filaments, but I'm thinking the constant power cycling in the filaments will thermally stress them, leading to premature failure. How would be best to leave a VFD when not using it? What sort of idle time should I set, if 10 seconds is too short? An hour would work?

Improve this question
\$\endgroup\$
3
  • \$\begingroup\$ Link to display model / datasheet please? That or appnotes might reveal what is best for the display. There might be a soft-start feature so turning on the filaments might not be that detrimental. \$\endgroup\$ – Justme Jun 26 '20 at 17:06
  • \$\begingroup\$ The answer depends entirely on the kind of device that you're building, its user interface, and the user interaction that it needs while working. Does it work unattended? Does it need to show the task progress, or time left, or time spent? Does the user need to check or change the device settings many times? Maybe you could set a "screen saver" graphics just to keep the display on, and preventing burn in or fading of phosphorus. Maybe you could use LEDs for showing that everything is OK, and light the VFD only if the user wants to change a setting. \$\endgroup\$ – mguima Jun 26 '20 at 17:48
  • \$\begingroup\$ The right technical solution should go after the design decisions (decisions about the device's user interface). A VFD can be always on, if needed: think about old microwaves oven and VCR's, theirs VFD were always on, just displaying a clock for most of times. Does your device runs on battery or it is AC powered (probably AC)? \$\endgroup\$ – mguima Jun 26 '20 at 17:59
1
\$\begingroup\$

Typical lifetime of a VFD display is 30,000 hours, and the luminance of the fluorescent phosphor (typically 505nm ZnO:Zn) will fade as well as evaporation of the filaments.

VFD filaments run at relatively low temperature so I wouldn't worry too much about cycling, but you might want to blank the display and turn the filaments off to save power and prevent burn-in.

The delay you use has more to do with your application and whether a slight delay coming back up would be an issue. You could blank the display quickly and turn the filaments off after a longer delay if there is a noticeable lag. I think there's a perceptible fractional-second lag in starting up my 1970s-era Casio "Computerized Quartz CQ-1".

enter image description here

Improve this answer
\$\endgroup\$
4
  • \$\begingroup\$ Power usage is not a concern in my application, nor is the short delay caused by blanking/turning off and on the fillaments. Burn-in is an issue I want to avoid, therefore, you're saying I should go with turning the display completely off when not in use? \$\endgroup\$ – LondonNight Jun 26 '20 at 17:27
  • \$\begingroup\$ Yes, I think I would avoid having it run 24/7 if possible. OLED displays, similarly. \$\endgroup\$ – Spehro Pefhany Jun 26 '20 at 17:40
  • \$\begingroup\$ Do you have Dim control in the design? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 26 '20 at 17:48
  • \$\begingroup\$ I'm not sure about dimming, I will have to look it up. As for PWM-ing the filaments, using AC... That's not possible for me. \$\endgroup\$ – LondonNight Jun 26 '20 at 18:02
0
\$\begingroup\$

I would use PWM to dim them with AC filament current so there is precise thermal rise current regulation.

Noritake VFD's have very high-quality today. You can use them continuously for the longest life. 20 years MTBF.

Phosphor displays actually last a shorter time each startup.

My Tri-phosphor T8 tube lamps for example are rated for 30kh when cycled 1/day but 50kh if left on 24x7. I don't know the exact values for these VFD's but I suggest PWM current control and ensure they are operated within specs.

"VFD character modules provide a high brightness distinct display with a service life exceeding 20 years due to their high MTBF (>1 million hours) and lower operating duty cycle and anode voltage. They are designed for -40C to +85C operating temperature."

http://www.noritake-itron.com/NewWeb/VFD/VFDCOver.shtml

Typical VFD modules operate from a 5-V ±5% dc supply with current consumption dependant on the particular component. They are compatible with transistor-transistor level (TTL) or CMOS I/O signals and deliver a typical luminance of 700 cd/m2 with a total viewing angle of 140°, mean time before failure (MTBF) of 80,000 to 100,000 hours (300,000 hours with design modifications), and a typical brightness degradation of 50,000 hours to half brightness. https://www.electronicdesign.com/technologies/displays/article/21771510/mature-display-technology-still-viable-in-advancing-markets

For extended life with low duty cycle, expect 1e6 hr MTBF. You can interpolate the MTBF with minimal burn-in effects using the DIM feature on multiplexing.

So it's your choice. On/Off or Bright/Dim.

Improve this answer
\$\endgroup\$
2
  • \$\begingroup\$ T8 fluorescent tube lamps and VFDs operate very differently, one cannot make an analogy between the two when talking about their life hours. \$\endgroup\$ – LondonNight Jun 26 '20 at 17:29
  • \$\begingroup\$ True yet these are sensitive to mechanical and thermal shock. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 26 '20 at 17:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.