This time the longest post in my history . I hope you won't kill me for length of this post and neither for my English (I'm not native-English-speaker )
Everything I have written is based on my observation and experience in electronic circuits. All information that I compiled below in this review I found using a Google-fu
- 0. Intro - why
- 1. The Package - (not so black-)box content
- 2. The Sandwich - unfortunately not eatable, but how things fit
- 3. The Display - closer look on display module
- 4. Testing under Windows -
- 5. Teardown -
- 6. Raspbian tests -
- 7. Summary - Plus and Minus
- 8. Configuration - setting up display & touch on Raspbian Jessie 2017-01-11 -
I ordered some time ago a new display for RPi of (disliked till now by me) a brand: KeDei . There might be some people who know, that I don't really liked those KeDei displays, they looks cool and slick, but no driver code and they slowness was so irritating. I even attempted to rebuild the spi interface so it might be used with fbtft but I gave up (and the display gave up too ).
Now you think: "Wait, wait, wait, he bought next KeDei display!? Did he hit his head too hard?!"
Ok, my head is fine I found this new version of KeDei display while digging through aliexpress for 3,5" TFT display. So I ordered one and give a chance for KeDei to redeem his sins committed on previous displays ...
I got a package right before weekend so I can play with it
All photos are here at my google drive: https://drive.google.com/drive/folders/ ... ndWY2VhTUk
1. The Package
Display was packed in small cardboard box with that white foam, and the box was put into plastic-bag envelope. In box I found a HDMI bridge, stylus and display : Pretty standard content for the HDMI display with touch for SBCs
Photos here: https://drive.google.com/open?id=0BySjz ... TB2Y2MxbjQ
The display looks fine, there is a little of solder flux leftover on board but that might be only in my display, and I'm not bothered by it anyway.
The hdmi bridge - yeah, I have to complain about something : it's dirty, there are a residues (the white "thing") from cleaning after soldering - this looks really untasteful....
As for stylus, nothing really to comment, the tip is smooth - don't have any sharp edge.
2. The Sandwich
Let see now how the display fits RPi. I got recently Raspberry Pi 2.2 (Pi2 v1.2 , but "2.2" sounds and looks better ) : More photos in HQ: https://drive.google.com/open?id=0BySjz ... VpqVEdWc1E
AS you can see, the HDMI socket is a slight off to RPi HDMI socket, so to connect the display with the bridge you have to a twist and bend a little the display board. You can see this on photos. The hdmi bridge is too short or the GPIO connectors are too long (pick one ).
The best way to fix this would be to desolder the GPIO connectors, remove one spacer, put the display together with RPi and de-soldered GPIO connectors, then solder the GPIO connector back to the display board.
3. The Display
Let's take a look at display Photos: https://drive.google.com/open?id=0BySjz ... HdiUEpINHc
There is few chips on the board and the GPIO connector is split into two parts (that's common in kedei displays), also we got a microusb for power, jack 3,5mm for audio output and backlight switch - YES! (but I bet there will be personas that would want to control the backlight from GPIO pin :D )
Now, let's take a closer look at parts we've got on display:
- RTD2660H - It's main performer here - Realtek RTD2660H is a "Flat panel controller" - it support a lot of video inputs (HDMI/DVI/VGA/S-VIDEO(composite)) and have two video outputs: LVDS and TTL, it have audio decoder, DDC, MCU core and even OSD - hmmm... this looks like it could be installed on those boards-adapters HDMI/DVI/VGA to LVDS that are for ~14USD on aliexpress... Anyway, in KeDei it have only HDMI input used, as for output I'm not sure, but it might have very likely used a TTL output mode.
- 25X40 - Winbond W25X40CLNIG - 4Mbit SPI NOR-Flash memory - there is probably a firmware for MCU inside RTD to init display & show "KeDei logo"
- CS4334K - Cirrus Logic CS4334 (It's been a while since I saw this name...) - It's a 24bit 96kHz stereo D/A converter with 16..24bit I2S interface.
- XPT2046 - Shenzhen Xptek Technology XPT2046 - a resistive touch panel controller with SPI interface - no need for more comment
- 4103 - PowerTech PT4103 - it's a tiny (chassis SOT-23-6) step-up dc/dc white led driver - next one popular chip
- AMS1117-x.x (where "x.x" is voltage) - are voltage regulators for RTD & display panel - the 1.8V looks ok, but marking on 3.3V version looks soo strange, that I would say it's some clone of AMS1117...
- Display connector - It's a fine-pitch (0.3mm) connector with 39 pins - Yeah, I counted them
- Backlight switch - very demanded function in those small displays, in this one we don't break only backlight led circuit but we switch off whole backlight driver (turn off power to PT4103),
- Micro Usb - Only for powering the display & Pi, you should use only one: On RPi or on the display, but the one on display is not protected by fuse and connects directly to RPi 5V bus
- Touch panel - not much to comment but I should mention that the FPC cable from touch panel is directly soldered to PCB, this is a reason of the piece of tape on display...
- Raspberry Pi GPIO connector - It's used to power the display module (or power the Pi - depends where you plug the power cable: to the Pi or to the display), and for touch panel controller interface - the XPT2046 is connected to SPI and use CS0 for chip select.
- The Display - it's a 320x480 TFT panel with 18bit RGB I/F, part number (in my module): S90329A-DT035HV , very likely manufactured by Yunlea . Googling for DT035HV reveled a link to very similar (in size and FPC pinout) display: S90456B-DT035HV - difference is only on length of FPC connector and it's distance from display edge. As for viewing angles, they are not so bad for a normal TFT (or at least for me ).
The user shahidali55 (topic: viewtopic.php?p=1247639#p1247639 ) found out the Aliexpress seller who might have exactly the same display: https://www.aliexpress.com/item/3-5-inc ... 87937.html - Looking at the photos on aliexpress the fpc and marking seems for me identical.
According to the information from aliexpress:
- Controller: ILI9481B
- Interface: Selectable: SPI or parallel RGB 18bit
- Backlight: 7 white leds.
- Touchpanel - resistive 4 wires, for 3.5" displays 82x54mm size. The FPC from touch panel is soldered directly to PCB.
4. Windows testing
Yeaaaa, windows 10. So I hooked the display to my laptop to HDMI. It have a scaler built-in into but it have it's limits too , so on movie this look bad, I managed later to setup my GPU so it could output some more (lower and) reasonable resolution that work much better with screen. Photos are on my GDrive (link up) :
Photos: https://drive.google.com/open?id=0BySjz ... mxtbTJJT1k
OK, display working , time to break it apart! I wouldn't be myself if I won't do it , let's have a look what is under the TFT panel
If somebody noticed a black wire on photos then you'll see it's purpose
No photo in post - forum limit 3 attachments
Check the photos on google drive: https://drive.google.com/open?id=0BySjz ... ENpVVhkMnc
Display is glued to PCB with double-sided adhesive foam - there is 2 long pieces of it, but on photos I had them short already, it came off much easier that in previous version but the touch panel FPC is soldered to PCB and you have to really be careful with it (I pulled it a little too much and, now I had to put a piece of foam on the FPC soldered to PCB and squeeze it down with piece of tape so I have a electrical contact...)
Now you see what is going with the black wire - it's grounding for display metal frame
The display connector as mentions have 0.3mm pitch... And in my board the soldering is nooooot so beautiful
Putting it together took mi a bit more time than breaking apart, I had to play around with positioning the tft panel around to make the display FPC fit nicely into it'd connector, and also not having the FPC from touch panel bent too much, too.
You'll be able to see this tape on video with testing the display on Raspbian
6. Raspberry Pi Tests
Image quality is not so bad, on photos & movies it came off a much more blue/colder than it is really. Backlight it not so dark but might be a little stronger so the display would be a brighter.
Test video: Sintel 1080p 24fps and Big Buck Bunny 1080p 30fps
Photos: https://drive.google.com/open?id=0BySjz ... UFzaXJRVUU
Photos: https://drive.google.com/open?id=0BySjz ... HVEMnBtVTQ
Photos: https://drive.google.com/open?id=0BySjz ... WVtUDF4Sk0
This time KeDei did a good job with this display, they must see that users were complaining a lot because of very low fps, they must take those to heart and designed a nice piece of hardware. With the moving from SPI to HDMI for displaying, now we can run console emulators, play h264 video and do other things that fully utilize GPU in SoC on RPi , and of course, use of HDMI allow to connect this display to other SBCs too .
So the "pluses":
- HDMI - allow to connect practically any video source to the display (laptop PC/ Raspberry/Orange/Bana -Pi / BBB / etc)
- Audio output - stereo 3,5mm jack
- Size of Raspberry Pi
- XPT2046 touch
- MicroUSB for powering display and Pi
- No need for propriety drivers (per-compiled kernel) from KeDei
- built-in video scaler
- Backlight switch
- Price: ~25USD with shipping for 3,5" & touch display with HDMI - for 27USD with shipping you can get 5" display with HDMI input
- Don't fit so good, the display sits awry on Pi
- Too long GPIO connectors/too short HDMI bridge
- Touch panel FPC soldered directly to PCB
- The RTD get a pretty warm with whole board
- No fuse(polyfuse) on MicroUSB power connector, especially because it's connected direct;y to 5V bus on RPi
- Display is a bit too dark
In next post I'll put an instructions how to setup the display & touch using latest raspbian (this make it easier to link-up than scrolling through my post ).
-- Changelog --
- 2018-01-03 - Added some display info.