Can I add backlighting to this instrument? - Page 1
Forum section: electronics / projects

author: daisizhou
author_rank: Super Contributor
timestamp: December 04, 2024, 06:05:14 am
content: Hallo everyoneThis is a meter on a power analyzer.Since it has no backlight, sometimes it is difficult to see the screen display clearly in a dark environment.So I plan to use light-emitting diodes as a light source to add a backlight display to this screen,I don't know if my plan is feasible.I haven't found any more information about this screen. If you can find it, I hope you can tell me. Thank you.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 04, 2024, 06:12:02 am
content: Backlight, or frontlight?I suggest you remove the PCB and display module from the plastic enclosure. The PCB forms tabs into the enclosure, and I don't see any screws, so a spudger or thin flat screwdriver will help.You'll find out whether it is viable by looking at the actual display module between the PCB and the plastic enclosure.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 04, 2024, 06:44:12 am
content: If the LCD is purely reflective (which I suspect), there's no backlight possible that I know of. But that'll be "frontlight", as Nominal suggested.Then you'll just have to place maybe one LED on each side of the panel, which will illuminate the front of the LCD. Just like (reflective) LCD watches do. No need to try and get access to the back of the LCD again, as I don't think you can "backlight" it anyway.

author: daisizhou
author_rank: Super Contributor
timestamp: December 04, 2024, 09:00:58 am
content: My plan is this, as shown in the figure below, there is a white LED on each side.Light passing through clear glass.The two LEDs require a voltage of about 3V. I hope to connect them directly to the rear PCB, but I am not sure whether it will affect the measurement, so I have not started.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 04, 2024, 09:43:15 am
content: Yes, that should be fine. You need to power them with a supply that is able to provide the required current obviously (don't forget a series resistor). As to noise otherwise, as long as you don't PWM them, it shouldn't not add much noise at all to the power rail.Using small light diffusers on each side would give better frontlighting, but it'll work without that.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 04, 2024, 10:15:44 am
content: Quote from: daisizhou on December 04, 2024, 09:00:58 amWhy would that work? Surely the glass will work like a light pipe. There would seem to be no reason why the light would exit the glass and illuminate the face of the display. You would need to abrade the surface of the glass to make it leak light out sideways.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 04, 2024, 10:43:51 am
content: Quote from: SteveThackery on December 04, 2024, 10:15:44 amBecause of the silvered foil on one side of the display. It is not mirror-like like the total internal reflection surface would be, and it is diffusive enough to make it work.How do I know? Because several of my 1" - 3.5" TFT display modules do backlighting that way, using two to six (side-emitting?) white LEDs, depending on the display module size. It is notexactlythe same, but I've also seen it used on DMMs with exactly this kind of reflective foil backing, too.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 04, 2024, 10:56:48 am
content: is it a voltmeter ?? is there a led variant of this one ?as other wrote i don't think putting led behind the lcd will work, and you need a light difuser too, witch in turn thicken the display

author: squadchannel
author_rank: Frequent Contributor
timestamp: December 04, 2024, 11:03:22 am
content: Thinklight?

author: daisizhou
author_rank: Super Contributor
timestamp: December 04, 2024, 11:46:34 am
content: I tried googling "UP-6000" or "D2868"。I hope to find the schematic diagram of this instrument or more detailed information and data, but unfortunately I have not found anything.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 04, 2024, 11:51:47 am
content: Quote from: Nominal Animal on December 04, 2024, 10:43:51 amI'm sorry, I still can't visualise it. The drawing by@daisizhouseems to be of a clear sheet of glass (not unlike a microscope slide, but smaller) placed on top of the display, with light sent into it from each side. Obviously I've got that wrong because light will not exit the glass sheet to illuminate the display unless the glass is etched in some way to cause scatter.So where is this silvered foil? And is it in physical contact with the glass? Because if it isn't it won't cause any light to leak from the glass.I apologise - I've obviously got completely the wrong picture in my head. A diagram might be good.

author: daisizhou
author_rank: Super Contributor
timestamp: December 04, 2024, 12:41:00 pm
content: Sorry, I have drawn a simple schematic diagram of the LCD display screen.Usually, the front of the glass is for display, and the back is covered with a silver reflective film

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 04, 2024, 01:24:58 pm
content: Quote from: SteveThackery on December 04, 2024, 11:51:47 amIt will, if the foil is directly on the glass surface without any gap in between, because total internal reflection is from glass-air interface. If the glass-foil interface has a higher refractive index, then the light will scatter and the backlight work.Seethis Newhaven display modulefor an example. You can see the exact same type of foil, with the LED diffuser on the right side. It is a sector to ensure even lighting from a single LED.

author: pienari
author_rank: Regular Contributor
timestamp: December 04, 2024, 03:34:23 pm
content: My lab psu uses 2pcs same meters.I have drilled 3mm holes both side of the plastic frame and installed green leds.It works but not perfect solution.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 04, 2024, 05:03:50 pm
content: Quote from: Nominal Animal on December 04, 2024, 01:24:58 pmHang on, that's a totally different thing, isn't it? That appears to send the light through the LCD glass itself. Of course if the back of the LCD glass is frosted, or touching the foil, light will be scattered, as we need.But@daisizhouseemed to be talking about puttinganotherlayer of glassin frontof the display, and sending light into either side of it. That won't work well because the light will stay inside the glass unless the glass is etched (or even scratched or dirty).So what is the proposed solution? Illuminating the LCD glass itself from the side? (That will work if the back of the glass is in contact with something like reflective foil.) Or an extra layer of glass in front of the display? (That won't work unless the glass is treated in some way so it leaks light out of the back face.)

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 04, 2024, 07:32:43 pm
content: Quote from: SteveThackery on December 04, 2024, 05:03:50 pmNo, that won't work; you'd need most of the light to be reflected on the display side, as otherwise you'd be washing out the display by the light scattered in front of the LCD. I always understood them to intend to side illuminate the existing display module glass layer, no added new layers. The other option is to have external LEDs outside the display module, in the plastic enclosure part, directed towards the display, away from the viewer.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: December 04, 2024, 10:00:23 pm
content: Quote from: daisizhou on December 04, 2024, 06:05:14 amYou would need to remove from the housing to see how much room is available, and experiment with various light injection to see how feasible.It will never match a true backlit display, but you might manage ‘good enough to read’ in the dark.

author: daisizhou
author_rank: Super Contributor
timestamp: September 25, 2025, 10:52:38 am
content: Hallo everyoneAfter more than half a year of use, I still couldn't stand the lack of backlighting, so I decided to add LED backlighting.I have never been able to find the pin definition and data sheet of this instrument. In other words, I don't know where the backlight LED power supply voltage should be obtained.Because it seems that the instrument has a measurement function and seems to have requirements for measurement accuracy, I can't blindly obtain the voltage.If anyone knows the datasheet or pin definition of this instrument, please let me know. Thanks

author: Nominal Animal
author_rank: Super Contributor
timestamp: September 26, 2025, 04:24:19 am
content: Have you tested externally powered white LEDs would work sufficiently well?I would put three side-emitting LEDs or suitable 3mm LEDs in the positions marked with red spots in the attached image, kept in place somehow (blu-tack, clay, a 3D-printed temporary strut), and see if the lighting that provides works well. The LEDs are best placed in direct contact with the glass surface, to reduce reflections, so for through-hole LEDs, look for flat-topped ones. You can also carefully file one side of round/cylindrical LEDs flat, so it will sit nicely on the greenish flat surface.If you can get that working sufficiently well, you know your voltage and current requirements.My next step then would be to measure the power meter connections to the display module, to find out which one is the power supply. (My guess is the red and black wires are the supply.) You'll likely need something like 3.0V – 3.4V at a few mA per LED, with multiple LEDs used to get more even lightning pattern, and not to get more light. I suspect you'll find the supply is something like 5V – 12V.I personally would use three (on one side) or six (three per side) LEDs, all from the same batch, selected and verified to have the same forward voltage at the desired current, so that I could put them all in parallel. Then, I would use a suitable linear regulator with adjust pin, perhaps an LP2951, in constant current source configuration (seeTI TIDU922A, circuit configurations A and B on pages 7 and 8). This way, the backlight intensity would always be constant, without any significant effect on the display module or the whole meter, assuming the current needed is small (maybe a dozen or two milliamps).While you could simply use a current-limiting resistor (for all LEDs in parallel, or separately for each LED), the LED currents would still be highly sensitive to the supply voltage. I do not know meter innards, but on the devices I've poked, the internal supplies do vary depending on which subsystems are enabled or which mode the device is in; perhaps not by that much, but enough for me to detect when backlight uses only current-limiting resistors. The intensity change feels "wrong" to me, so I personally would definitely spend the extra 1 EUR or 8 CHN on the "over-engineered constant-current source" for lighting the LEDs.If you cannot find a suitable supply on the display module connectors, you could always add one, using e.g. a pair of single-core wires twisted together and terminated with a PH2.0 or similar power connector, and find a suitable supply elsewhere in the meter.

author: jonovid
author_rank: Super Contributor
timestamp: September 26, 2025, 06:45:02 am
content: Liquid Crystal Display LED Backlight Modmy LED Backlight modification to a LCD DMM

author: Nominal Animal
author_rank: Super Contributor
timestamp: September 26, 2025, 10:58:20 am
content: Multiple LEDs per side, wider-angle LEDs, or perhaps a diffusor (a thin transparent piece of plastic you scuff up with sandpaper) might help make the light more even. If one uses a diffusor, then the LEDs are better placed away from the diffusor, not in direct contact.Placement and LED direction is pretty critical, and I think caused the bright side spots in jonovid's (rather than the display construction). I do believe that with a bit more experimentation first (more diffuse LEDs, or a diffusor, pointing the LEDs carefully, even adding shadow baffles to minimize direct line of sight to the LED itself) would have gotten jonovid better results; but otherwise it is exactly how I'd do it too.Experimenting with LED placement (powering the LEDs from an external power, measuring the current used) before any permanent installation is in my opinion absolutely necessary here.

author: daisizhou
author_rank: Super Contributor
timestamp: September 26, 2025, 11:19:02 am
content: ThanksThe effect seems to be very good

author: coromonadalix
author_rank: Super Contributor
timestamp: September 26, 2025, 01:05:07 pm
content: i do think they are slightly too bright but it's me ...

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 01, 2025, 05:36:11 am
content: You might be able to cut down the direct LED glare using a small piece of aluminium foil tape, between the LED and outermost glass-and-mask.Not only is the foil tape very opaque, but it also reflects the LED light back, hopefully scattering it towards the glass layer more.Also, a thin diffuse piece of plastic between the LED and the glass layers may help a lot with the evenness.You can do this by taking any thin piece of plastic sheet (say, from molded packaging), then sanding it on the LED side using very fine sandpaper (400 grit or higher), and then cutting it into a small piece covering the glass ends.