Multimeters why not LCD? - Page 1
Forum section: electronics / beginners

author: PsychoBoy
author_rank: Contributor
timestamp: May 15, 2019, 03:46:44 pm
content: So I was dreaming last night about creating my own multimeter (it's just dreams though) and wondering why all multimeters use this customized LED display panels instead of modern LCD? Is it just much cheaper? Or maybe it is more immune to impact etc?Cheers

author: Nerull
author_rank: Frequent Contributor
timestamp: May 15, 2019, 03:54:56 pm
content: Most multimeters use LCDs. I haven't seen a LED character display on anything but cheap panel meters in ages.

author: Benta
author_rank: Super Contributor
timestamp: May 15, 2019, 04:14:17 pm
content: Don't think I've seen a hand-held DMM with LEDs for decades, only LCD.On desktop types you see LED or OLED or other graphic types.

author: Berni
author_rank: Super Contributor
timestamp: May 15, 2019, 04:38:39 pm
content: I think he means why multimeters use custom made 7 segment LCD panels rather than a graphical matrix LCD.Part of it might be because of history but mostly because they don't actually bring much benefit to multimeters with basic functionality. They don't need to display more than numbers plus a few fixed symbols, while these segmented displays can provide a sharper and more contrasting image.I do admit i am not a fan of these LCD displays. My favorite handheld meter so far is the Agilent U1273 with its OLED display. For indoor use (Where i use it all the time anyway) it greatly improves the readability of the display while still providing better battery life than a lot of LCD display meters.As for bench DMMs i love VFD displays. They have excellent readability from all angles and in the dark and can support a large number of segments/symbols.

author: PsychoBoy
author_rank: Contributor
timestamp: May 15, 2019, 04:56:20 pm
content: Sorry guys I didn't know they are LCD's, I thought it uses simple LED's.Quote from: Berni on May 15, 2019, 04:38:39 pmExactly, I was wondering why they don't use this LCD dot matrix displays like for example TFT 128x160 pixels or something, I mean isn't it more expensive to design your own custom LCD display rather than pick off-the-shelf LCD dot matrix module?I understand argument that they don't need such display although I find it useful as it could have much more functionality. Anyway the thing I wondered is if there is any hard counter-argument to not have such dot-matrix LCDs in DMM?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 15, 2019, 05:00:15 pm
content: The custom LCDs are not that expensive in reasonable quantity and not all are really custom for a single meter. The graphical LCDs also need quite some extra power, while the B&W displays with 7 seg and extra symbols can be really low power. They are also often better readable - especially the older graphical LCDs had often poor contrast.The LED displays in early bench top DMMs where often made from standard 7 segment / 15 segment digits. They are also very nice to read and long lasting compared to OLED or VFD. They are just limited in showing special symbols and letters already may look a little odd.Quite some new bench top DMMs use graphical LCDs.

author: mariush
author_rank: Super Contributor
timestamp: May 15, 2019, 05:13:33 pm
content: There are all in one multimeter chips which have build in lcd driver, so they can drive the lcd segments directly. It saves money if you don't need extra lcd driver chips to increase power consumption along with chips on the back of the lcd displays (for row/column processing and all that).Other multimeter chips have i2c or SPI or some other method of transmitting data to a microcontroller, and then a microcontroller formats data and sends it to a graphical/segment LCD display.For multimeter companies it's cheap to make these 7 segment displays because they can reuse them with multiple multimeters or versions of the same multimeter ex see Uni-T UT139 series ...

author: Tom45
author_rank: Frequent Contributor
timestamp: May 15, 2019, 05:22:42 pm
content: Using a pixel display rather than fixed segments would allow much greater flexibility in what could be displayed in the various modes.However, the extra cost in firmware and processing time to paint a pixel display would likely slow down display response. And would certainly result in a higher cost meter.A meter with a pixel display and open source firmware could lead to an interesting variety of new features once the experimenters got their hands on it.

author: PsychoBoy
author_rank: Contributor
timestamp: May 15, 2019, 05:50:27 pm
content: Got it, thanks all, so it is mix of production cost, low power consumption and easy implementation.Quote from: Tom45 on May 15, 2019, 05:22:42 pmThat's what I exactly thought, seems like it isn't huge problem to install such a display but the bigger is to implement a firmware, if indeed DMMs are single chip solutions.Anyway nowadays I think it's not a problem to put powerful lot-power consumption ARM processor.Thanks everyone for answering

author: newbrain
author_rank: Super Contributor
timestamp: May 15, 2019, 10:13:27 pm
content: Quote from: PsychoBoy on May 15, 2019, 04:56:20 pmOur kind host has a number of videos on this very subject, you might be surprised at the price for a custom LCD: