Multimeter Display Perked Up With Nixies, LEDs, And Neon Tubes

Just because something is newer than something else doesn’t automatically make it better. Of course the opposite is also true, but when it comes to displays on bench multimeters, a fancy LCD display is no guarantee of legibility. Take the Hewlett Packard HP 3478A multimeter; the stock transflective display with its 14-segment characters is so hard to read that people usually have to add a backlight to use it.

That wasn’t good enough for [cyclotronboy], though, who chose to completely replace the stock 3478A display with Nixie tubes. He noticed that with a little modification, six IN-17 tubes just fit in the window vacated by the LCD. He sniffed out the serial data stream going to the display with a collection of XOR gates and flip-flops, which let him write the code for a PIC18F4550. The finished display adds a trio of rectangular LEDs for the + and – indicators, and an HDLO-1414 four-character alphanumeric display to indicate units and the like. And the decimal points? Tiny neon bulbs. It already looks miles better than the stock display, and with the addition of a red filter, it should look even better.

If you’re stuck with a lame LCD multimeter but Nixies don’t quite do it for you, worry not – an LED conversion is possible too.

6 thoughts on “Multimeter Display Perked Up With Nixies, LEDs, And Neon Tubes

  1. Very nice, but my HP 5326b counter-timer-dvm CAME with Nixies and still works great; to the best of my knowledge it has never been repaired. Within 0.02 volts of a modern 4 digit meter after a few minutes. Don’t make em like they used to.

    WHAT did they use in the capacitors 45 years ago?

    Extra props for using the now fabulously expensive smart LED display (I use my small supply only for “important” projects).

    The builder could get amber plexiglass for the Nixies and red for the LED’s. If cut and sanded this can be glued together on the edge seamlessly.

  2. My 3478A units are also perfectly legible, and the 14 segement displays are perfect for the job… Not as nice as the VFDs on the later stuff but still fine, so I suspect it must of been a faulty display here?

    1. Actually, the link to the LED conversion really does show how poor the display is in comparison to LED! I always had mine right in front so I guess never suffered from the viewing angle issues…

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