Products > Test Equipment
Fluke 8840/42 Series Universal Replacement Display
Kjo:
--- Quote from: TheBay on November 24, 2021, 07:05:39 pm ---OLED Lifespan and burn in isn't a "Red Herring" issue at all, I've been using OLED's for years and unfortunately they do suffer badly with their brightness decreasing and also burn in. As impressive as your project is and I'm not knocking that, OLED really isn't ideal for this application.
Visibility won't be great in a lab as they are not that bright to begin with and most multimeters are left on for long periods of time often with many static digits.
--- End quote ---
I accept your experience with OLED devices, however none of the replacement approaches come with any long term reliability data and certainly haven't had quality endurance testing as a big name manufacturer might do. These blue LED replacements may fade in time! And I dont mean to indicate that using a OLED or LCD module is going to in any way be cost effective compared to this blue LED drop-in replacement. The OLED alone costs as much as the blue LED module! and the OLED still needs a 7 sq in PCB packed with circuits to convert the 30V signals and drive the graphics!
But my goal was to free the display part from the button PCB so that nothing needed to be re-soldered to the Fluke PCB. The OLED display is held in place by friction clips and can be easily removed albeit the meter has to be disassembled. I really wish I could find a full color LCD in this form factor! I could really create an interesting display with it. But, alas, I have not found one suitable.
In the photo below one can see the display and ribbon cable floating in the button frame opening. And in the second, the friction mounting clips. The third photo shows the controller PCB that mounts to the inside side of the display PCB. The controller interfaces to the display PCB to convey the button signals by plugging into the inboard original display interface socket. The ribbon cables from the main board plug into the controller sockets as they did to the original display PCB. No other connections are required other than the 5VDC power that is derived from the main board 5VDC supply. This way the display & controller remain isolated from the case on the internal in-guard side.
The switches (3) control the bootloader, display format options (7), and a display simulation mode. The controller is held in place by the one 16 pin socket on the original display PCB (hidden), a friction clip and a fortuitously located hole through the button retaining frame (yellow).
TheBay:
--- Quote from: james_s on November 24, 2021, 09:20:35 pm ---You're not going to be able to filter a blue LED to some other color. The VFD phosphor produces a quite broadband emission spectra, a blue LED is a fairly narrow spike. Since filtering is subtractive it doesn't really work with narrow band emitters.
--- End quote ---
That's what I was wondering when I said it has not much green in the spectrum, maybe a white LED and coloured filter would be a better approach.
For what it's worth I can't stand Blue LED's
james_s:
A white LED would certainly work, although those rely on a phoshor and in my experience white LED displays have the same problem as VFDs only worse. The best is a non-phosphor LED emitter in the desired color which do exist.
TheBay:
--- Quote from: Kjo on November 24, 2021, 12:17:12 am ---Rather than hijacking the thread "Fluke 8840A/AF 8842A VFD Display Replacement" I am starting a new one to outline my work in creating a 256x64 pixel graphics display to replace the VFD in Fluke 8840A/AF & 8842A multimeters. I have posted some of the basic work on the Fluke group over @ groups.io. But there is a lot of interest here and seemingly little crossover.
A quick caveat on both this thread work and that of the referenced thread. There is a very well made blue LED replacement module made by a group in the Ukraine in eastern Europe. It directly replaces the VFD on the PCB and is powered from the Fluke 5VDC test point. I bought 4 of them to repair several meters immediately. They are quite nice except for a few issues I will point out. The blue color shows through the Fluke smoked bezel better than a brand new VFD (I have one). If you look close at the picture you will see that the annunciation glyphs are considerably smaller than on the original VFD. It is a flaw that should be correctable, but I dont know the restrictions the designers were faced with. At ~$35USD & $5USD shipping you cant go wrong.
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It is a pain to remove an old VFD. Use lots of liquid or paste flux so as not to burn the pads or PCB. Suck out ALL the solder with a sucker or wick. Work from both sides. Once the old leads are loose, you have to carefully cut through the old mounting pads (4) with a box cutter, then clean the PCB. Nothing stronger than IPA or GooGone or you may damage the button conductive points. Then just follow the supplied assembly instructions.
KO3Y
--- End quote ---
It really is interesting and a cool thing you are doing, fair play to you.
I'm assuming these OLEDS are SSD1322 based or similar?
Is it possible to get a dot matrix graphical LCD in the same footprint and similar driver that would work too, as if you started making kits then the end user could chose OLED or LCD?
Kjo:
--- Quote from: TheBay on November 24, 2021, 09:29:50 pm ---I'm assuming these OLEDS are SSD1322 based or similar?
Is it possible to get a dot matrix graphical LCD in the same footprint and similar driver that would work too, as if you started making kits then the end user could chose OLED or LCD?
--- End quote ---
Yes, uses the SD1322 controller. Actually a rather PITA to work with considering that you cant easily address just one pixel. It requires a good bit of thought and planning and not easily amenable to bitmapped and scalable fonts.
I searched long and hard for a 256 x 64 LCD mono or color. I haven't yet found one. Maybe a forum visitor will see this and remember seeing one. I think, from what I have done, the minimum resolution needs to be 256 x 64 or higher with an aspect around 4 or 5:1. All of the small text in the display is one pixel wide fonts. I wish the OLED was brighter. I cant use the OEM bezel and be satisfied.
What is nice with this approach, though complex in firmware, is that the VFD grid and segment data is simply decoded on the fly. The bulk of the code is in decoding and extracting what should be displayed. The actual difference between the SD1322 and say a ST7735 display is just a couple of function calls.
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