Want to replace this TN LCD with a compatible IPS one... - Page 1
Forum section: electronics / projects

author: Logan
author_rank: Frequent Contributor
timestamp: May 28, 2022, 01:15:44 pm
content: Hello.I want to replace the LCD in 2 pictures (TM024HDH71) with an IPS one.It's Okay if the new panel have a different size(with same resolution of course), but the connector must be compatible both electronically and mechanically.The Datasheet of the original display is attached.Can anyone help me to find one from a well known brand? (Not some random aliexpress...)Thanks.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 28, 2022, 03:55:33 pm
content: I suspect that is going to be quite hard to find, unless you intend to buy a lot of them.I've used a couple of BuyDisplay/EastRising2.8" 240x320 IPS displayswith the same ILI9341 controller. It is a well known manufacturer, that does sellon eBayas well. The display is slightly larger (69.3mm × 50.2mm × 4mm outer dimensions, 43.2mm × 57.6mm display area), and uses a different pinout on the flex cable; plus, its backlight is four leds in parallel (3.2-3.4V at max. 80mA).Personally, I'd do a 50mm by 20mm adapter board with a 50-pin ZIF (0.5mm pitch) for the IPS display, and either another 30-pin ZIF (0.5mm pitch) or directly solder a 30-pin 0.5mm pitch FFC cable (Molex 15166 series) to connect to the original device. The board would rearrange the signal lines, set the IM0-IM3 for the correct mode (8080 16-bit parallel; IM0 high and IM1-3 low), and could have whatever is needed to drive the backlight (common cathode with four separate anodes; the driving voltage is same in both datasheets, but this panel can use much more current for the backlight leds).This will add to thethicknessof the display module, but aside from the backlight, would electrically and cable-wise stay the same. How to solve the backlight issue depends on the device, and whether the backlight is adjustable (PWM?) or not, but it shouldn't be a big problem.

author: Logan
author_rank: Frequent Contributor
timestamp: May 31, 2022, 02:45:26 pm
content: Quote from: Nominal Animal on May 28, 2022, 03:55:33 pmThank you very much.Unfortunately that's beyond my ability...BTW is it possible to convert such parallel digital signal from host, to something like composite or HDMI? Will it also be difficult?

author: strawberry
author_rank: Super Contributor
timestamp: May 31, 2022, 04:39:59 pm
content: I can think of FPGA to convert VGA/HDMI to parallel (HDMI scaling/resolution for 240x320 ??)if controller is MIPI or RGB capable, there is chance finding controller/converter IC/board

author: DavidAlfa
author_rank: Super Contributor
timestamp: May 31, 2022, 06:37:38 pm
content: It's just one display? For a device you own?Then for sure you'll have to make some kind of adapter.IPS will have different controllers than TN, might share most of the commands, but there're always some differences like gamma curves, internal DC charge pumps... It might work but probably give bad image.If don't have access to the firmware sources to modify the commands, it'll be really hard to fix.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 31, 2022, 09:57:41 pm
content: Quote from: DavidAlfa on May 31, 2022, 06:37:38 pmThe one I posted has the exact same controller, ILI9341. The only differences are the FPC pinout and backlight LED driving (4 in parallel, instead of 3 in series).

author: DavidAlfa
author_rank: Super Contributor
timestamp: June 01, 2022, 02:36:35 am
content: Hmm I hope you're right, they like to put IPS in everything, even if not true...

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 01, 2022, 09:10:10 am
content: Quote from: DavidAlfa on June 01, 2022, 02:36:35 amWell, I haven't examined the panel with a microscope or torn it to pieces (and even if I did, I'm not sure I can tell the difference in construction between TN and IPS), but it does have wide viewing angles and good image quality in my personal opinion; I've got two or three of these.In general terms, EastRising/BuyDisplay does have a good reputation among users of small display modules and panels, including here at EEVBlog.Furthermore, they do have both IPS and TN models of this:ER-TFT028-4with a TN panel, andER-TFT028A2-4with an IPS panel.TheirYoutube channeldoesn't have an example video yet of the IPS panel, only of the TN panel one.The only thing I've had 'issues' with these IPS-paneled ones, is how to drive the backlight. I'd prefer a programmable constant current drive instead of PWM (at a few hundred Hz), but PWM is easier. As described in thedatasheet, it has four common cathode backlight LEDs (pin 1 cathode, pin 2-5 anodes), each 3.2-3.4V forward voltage, and up to 20mA per LED, 80mA total.OP's module uses three LEDs in series, at max. 20mA, and with 2.9-3.4V forward voltage per LED, and thus is supplied 8.7-10.2V for the LEDs. (We know this, because the datasheet OP attached tells us the LEDs are in series, max. current is 20mA, forward voltage 2.9-3.4V per LED, and total consumption is 192mW: 3×20mA×3.2V = 192mW.)If I knew how to deal with that discrepancy, I could try to design such an adapter in EasyEda, so OP could order a set of five boards at JLCPCB for a couple of bucks plus shipping.Thing is, we don't know if the original backlight is controlled/adjustable, nor how. Pin 27 is LED anode and 28 is cathode in OP's FPC, but is it PWM'd or is it current-driven? Both? Is there a separate 5V pin we could steal the max. 80mA from? If the original LED supply is PWM'd, should the 80mA LED supply use that as the enable/PWM input signal? But again, that's probably a 10V signal. Or is there an external 5V signal we could use, perhaps with a small pot to set the current? How bright the backlight needs to be on the new display? It can provide up to 350 Cd/m², but we don't know how bright it needs to be. I personally prefer the backlight to not be so darn bright... I'm just a hobbyist, so I really don't know how to fix this electronically. Otherwise, I'm pretty sure the two display units are compatible.

author: Logan
author_rank: Frequent Contributor
timestamp: June 02, 2022, 12:47:54 pm
content: Thank you everyone!Quote from: DavidAlfa on May 31, 2022, 06:37:38 pmYes.Quote from: Nominal Animal on June 01, 2022, 09:10:10 amThe backlight is the only problem?(you said "The board would rearrange the signal lines, set the IM0-IM3 for the correct mode", that make me feel complex...)Okay if you can make a adapter diagram file, and just leave the backlight pin to a solderable pad, I can even pay you.The device is a Seek Reveal Pro, I think I can just connect the backlight to some power rail with a resistor.Thanks.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 02, 2022, 02:53:37 pm
content: Quote from: Logan on June 02, 2022, 12:47:54 pmYep. The BuyDisplay display supports a number of different modes, selected by pulling IM0, IM1, IM2, and IM3 to VCI (logic power) or GND; in this case, IM0 to VCI and the others to GND, because TM024HDH71 uses the "8080 MCU 16-bit interface I" mode of the ILI9341 controller. Other than those and the backlight, it's just routing the FPC cable pins in a different order, as both displays use the same ILI9341 controller.The schematic for this is attached, but NOT VERIFIED to be correct yet (EDIT: and yes, it had IM0, IM3, VDD, and VDI incorrect...); I need to check the pinouts again with fresh eyes, before I'll draw the PCB. (I'll try to do this tomorrow.) It'll take just an hour or less, and I find this fun. I'll put this up atoshwlab.com/nominalanimal, where all my other EasyEda designs end up also.If the device has a +5V rail somewhere, then four 100 Ohm resistors should work near perfect for the backlight. 0603 is small enough to put on a tiny interface board, but still hand-solderable.Quote from: Logan on June 02, 2022, 12:47:54 pmNo, just pay it forwards: help someone else in turn.

author: Logan
author_rank: Frequent Contributor
timestamp: June 02, 2022, 03:10:22 pm
content: Quote from: Nominal Animal on June 02, 2022, 02:53:37 pmOh my, You are such a generous gentleman! I don't know what to say... Hope all the best for your life.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 02, 2022, 04:47:23 pm
content: for the backlight you could use say an current limiter circuit with an lm 317http://lednique.com/power-supplies/lm317-constant-current-power-supply/https://www.bristolwatch.com/sr/cc_led.htmjust adding a resitter in serial will make it work, but i would not use it for a long term usage ...

author: Logan
author_rank: Frequent Contributor
timestamp: June 04, 2022, 01:22:20 pm
content: Oh I just saw the drawing by NominalAnimal:https://oshwlab.com/nominalanimal/buydisplay-er-tft028a2-to-seek-reveal-proThank you so much!

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 05, 2022, 11:42:39 pm
content: Quote from: coromonadalix on June 02, 2022, 04:47:23 pmLM317 would require about 8V or higher supply, though. OP's device does have one, but it probably is a current-limited at less than 25mA. (It might need a 470 Ohm resistor, as a stand-in for the series LED backlight.)The voltage drop over the backlight LEDs for the IPS panel is 3.0V to 3.4V (3.2V typical at 80mA), so if there is a well-regulated 5V supply, plain resistors will have about 60% efficiency. Four 100 Ohm resistors will then limit the current to about 80mA, 120 Ohm to 67mA, 150 Ohm to 53mA, and 180 Ohm to 44mA.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 06, 2022, 12:30:40 am
content: Okay, I think this version of the PCB ought to work. I consider this schematic and PCB design Public Domain orCC0-1.0: do whatever you want with it, but I cannot give any guarantees, only that Itriedto design something that works; but I'm just a hobbyist uncle bumblefuck, not an EE. Feel free to reuse the schematic or PCB design to make your own.You can open the schematic and the PCB directly atEasyEDA(no login required). If you open the PCB, you can use the 3D viewer to see how the board should look like in real life, with the connectors in place; and generate Gerber files (using the Fabricate > PCB Fabrication file (Gerber) or the G-folder-button) for manufacturing. You can either download the Gerber files as a Zip archive, or directly order the board (at your own risk, though!) from JLCPCB.Attached are the schematic and the 2D views of the PCB, as well as the dimensions of the display modules. It is a simple two-layer board, 42mm wide, 36.5mm tall.Note that the pin numbers at the connectors do not matter much, because these connectors have contacts on both top and bottom of the flex cable. I've used NetLabels for each net for this reason. If you open the schematic in EasyEda, and select the Design Manager tab on the left, you can expand the Net list and select any net, and EasyEda will highlight it for you in the schematic. Use this to check the pins, using the display datasheets as a reference.The 50-pin 0.5mm pitch connector is Omron Electronics XF3M-5015-1B (LCSC C231436). Note that this connector is used with reverse pin order, with the pin 1 mark on the connector housing referring to pin 50 (because it is used on the "back" side of the board); this is okay because the connector has contacts on both top and bottom sides of the flat flex cable. The pin numbers silkscreened on the board are the correct ones you should trust.The 30-pin 0.5mm pitch connector is Omron Electronics XF2M-3015-1A (LCSC C231418). It too has connectors on both top and bottom sides of the flat flex cable.You will also need a 30-pin 0.5mm pitch flat flex cable, for exampleLCSC C2857735(5cm long). When using a connector with contacts on both top and bottom, it does not matter whether this cable has connectors on the same or on opposite sides; both work.To install, first connect theER-TFT028A2-4to this adapter board via the 50-pin FPC. When looking at the display with the FPC hanging down, pin 1 is on the right. Place the display face down, so that pin 1 is on the left, and insert the cable to the connector. Then, gently place the board component side to the back of the display. You may need to use Kapton tape to secure the board, and to insulate the components from the back of the display. Next, insert the 30-pin FPC. Pin 1 is towards the center, and when flat, the contacts on the free end should be facing down. When gently folded back over the connector, the contacts will become visible. (I suggest using a 2mm stick, maybe a barbecue skewer or such, as a forming tool for the bend, as the cables may not like sharp creases.)Although the display module is slightly larger, the connectors should be offset so that the new display is centered wrt. the old one, just 6mm or so "thicker".The pads marked Load are the backlight from the Seek Reveal Pro. It is likely a constant current source, 20mA at 8.7V to 10.2V. If the host device monitors the backlight current source somehow, you can put a 470Ω or larger resistor (0603 or 0805 size) here. It will then dissipate up to 188mW of heat, so make sure you use at least a quarter-watt resistor. I'm hoping this isn't necessary, though.The ER-TFT028A2-4 backlight consists of four LEDs in parallel, with common cathode; each with a forward voltage of about 3.2V (3.4V max), and a maximum current of 20 mA per LED (80mA in total). The cathodes are connected to the through hole with a square pad, marked '-'. If you supply a regulated 5V to '+' and '-', you can use 100Ω, 120Ω, 150Ω, or 180Ω sixteenth-watt or higher 0603 or 0805 resistors, for 20mA, 17mA, 13mA, or 11mA per LED, respectively. I'd start with the 180Ω ones, only go with lower resistance if the display backlight needs to be brighter.Alternatively, you can use the '-' through hole for the common cathode, and the resistor pads on the connector side for the four anode inputs, and use a constant current to supply about 70mA in parallel, or about 17mA per LED; although I personally prefer slightly less.The reverse pinout on the two displays turns out to be super annoying. I used a crapton of vias (44) to make all sixteen parallel data tracks the same length (35.5mm according to EasyEda, all within a few µm), but the WR strobe is 20mm shorter (12.5mm); hopefully, this (about half a nanosecond propagation delay difference) should not matter.Edited on 2022-06-08 00:04:30 UTC: I forgot that ILI9341 recommends tying unused pins to ground or VDDI, so I modified the schematic and the board to tie the unused pins (VSYNC, HSYNC, DOTCLK, DE, DB17, DB16, SDO, SDI) to ground.

author: Logan
author_rank: Frequent Contributor
timestamp: June 07, 2022, 12:36:49 pm
content: Quote from: Nominal Animal on June 06, 2022, 12:30:40 amThank you so much!The device is not currently at my hand, but I'll report back in the future.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 07, 2022, 10:57:36 pm
content: No worries!I created asecond board, this time witheverything on the same side, so that one can use the JLCPCB assembly service to make the board(s). This too is Public Domain/CC0-1.0.It is 46mm wide and 36mm tall, two-sided board (with components only on one side). The same connectors are used in this one, except that since both are in normal orientation, the pin numbering matches the datasheets. I noticed that mikeselectricstuff had a teardown and a video on this device from 2016 (thread here), you see. I didn't see any obvious points to steal power from, but folding the 30-pin FPC at an angle should work; this one is designed for a 5cm/2" 30-pin FPC –– the same three components from LCSC as above. For simplicity, I put the backlight LEDs in parallel with just a single + and - through hole (needs a constant current of about 60-70mA, max. 80mA). The 0603/0805 pad is still there, if the Seek Reveal Pro needs a load on its backlight to work; a 470 Ohm resistor should work there.The length difference between the shortest (CS) and longest (D15) signal tracks is about 16.5mm, which corresponds to about a third of a nanosecond propagation delay difference. I think that is okay for the ILI9341 controller, since it specifies ≤15ns rise and fall times (30%-70%) in the datasheet.Attached is the slightly different schematic (open in EasyEda), board images (open in EasyEda), and a 3D picture so you can have a better idea of how it would look. (This connects unused signal pins to GND, too; I modified the earlier one to do so too.)When laid out this way, it is obvious how similar the two displays' pinouts are. This is as expected, since they do use the same ILI9341 controller.BuyDisplay does have a2.4" IPS displaywith the same connector and pinout (except backlight LED polarity inverted) as the 2.8" one, but it uses ST7789V controller instead of ILI9341. These are very similar controllers, close enough for many microcontroller libraries supporting these displays to support both with very minor differences, but it'd be too much to hope that the Seek Reveal Pro supported ST7789V. Otherwise, it'd bealmostwithin FPC bodges and hacks to do a replacement...

author: Logan
author_rank: Frequent Contributor
timestamp: June 09, 2022, 02:07:50 pm
content: Quote from: Nominal Animal on June 07, 2022, 10:57:36 pmYou're amazing!Your designs are really beautiful, like arts.BTW, why can't we just connect the new backlight to the host with proper value resistors? So that the overall diagram is simpler, and can be controlled by host.Just need to limit the current so it won't overload the host.Or it won't work with too little current? I think it would just be darker...Thanks a lot!

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 09, 2022, 11:30:25 pm
content: Quote from: Logan on June 09, 2022, 02:07:50 pmA resistor won't work right with a constant current supply, but perhaps one could use a 6V Zener diode to lift the forward voltage of the four paralleled LEDs, maybe a 1N5233?At the 10-20mA current that the device currently drives the backlight, the Zener drops roughly as much as two white LEDs in series, leaving the last "third" for the four parallel LEDs.The Seek Reveal Pro doesn't look too bright, so I suspect it runs its backlight at a lower current, maybe 10mA? Then, the four backlight LEDs on the IPS panel would ran at just 2.5mA each (since they are in parallel) instead of the max. 20mA; they'll be quite dim.If this was my device, I'd do some very careful examination of the board to see what kind of power rails are available on the Seek Reveal Pro, before choosing a particular method of driving the backlight. If there is a 5V rail that one can steal the 80mA from (say, if loading it with a 47 Ohm resistor, turning a bit over half a watt into heat, does not cause any issues – make that three 150 Ohm quarter-watt resistors in parallel), then a linear LED driver (like BCR421U) can be used to regulate the current with 66% efficiency (the needed voltage drop from 5V down to the LED forward voltage of 3.2-3.4V is wasted in the driver, generating up to 144mW of waste heat).I suspect the best option would be something like TILM27951. It could work either directly from the Li-ion battery (with ENABLE signal stolen somewhere on the board and PWM either from the original LED backlight via a level shifter (it being higher voltage) or from somewhere on the board), or from any 3V - 5V rail present. It only needs a pair of X7R 1µF ceramic capacitors, a pair of X5R 3.3µF ceramic capacitors, and a 14k-15kOhm resistor (to set the per-LED current to 250/R). The converter efficiency is at least 78% (worst, at 3.6V input voltage or so), but is 90%+ at 3.0-3.3V and 3.9-5V input voltage ranges. However, this IC seems to be unobtainium at this moment, and I'm not sure if there are equivalent ICs available... maybe MPS MP1519?I could add the LM27951 to the schematic, straight from the datasheet, but I haven't used it yet myself... And they could be really hard to actually obtain right now (year 2022) anyway.

author: Logan
author_rank: Frequent Contributor
timestamp: June 12, 2022, 02:01:06 pm
content: Quote from: Nominal Animal on June 09, 2022, 11:30:25 pmThank you a lot!No need to draw another with the driver chip, I will test the display first.