squalldna
Posts: 4
Joined: Sat Aug 19, 2017 8:53 am

3.5 tft lcd very laggy low frame rate

Tue Nov 27, 2018 2:58 pm

Hi. I bought a 3.5 lcd tft at aliexpress. I was able to install it using goodtft. The driver i used was 3.5 lcd A. Installed it on both my existing raspbian stretch, aswell as an image with drivers already setup. However, both showed now promising frame rate. It's so terrible i cant keep track of my mouse pointer. Does this have something to do with the setup, or is it the lcd device itself? Any comment would be appreciated. Also, i noticed that common 3.5 lcd have different back board compared to mine which shoes the flex cable on the back. The rest only have chips on it.
IMG_20181127_224658-816x460.jpg
IMG_20181127_224658-816x460.jpg (120.88 KiB) Viewed 729 times

User avatar
hansotten
Posts: 322
Joined: Fri Jul 13, 2012 6:01 am
Contact: Website

Re: 3.5 tft lcd very laggy low frame rate

Tue Nov 27, 2018 3:08 pm

If the driver delivers an image that means you are in luck: the driver is functional.

Most of these tft displays come with closed drivers and/or just an OS image you cant update.

These tft's are not very fast, due to low spi transfer rates and not optimized hardware and driver.
Have a look at what you can influence in SPI transfer rate in OS settings.This may help: https://www.raspberrypi.org/documentati ... /README.md

You get what you paid for: a cheap, functional but slow display.
http://duinorasp.hansotten.com for Raspberry Pi and Arduino and ESP8266
http://retro.hansotten.nl for retrocomputing with the 6502 cpu

squalldna
Posts: 4
Joined: Sat Aug 19, 2017 8:53 am

Re: 3.5 tft lcd very laggy low frame rate

Wed Nov 28, 2018 11:42 am

hansotten wrote:
Tue Nov 27, 2018 3:08 pm
If the driver delivers an image that means you are in luck: the driver is functional.

Most of these tft displays come with closed drivers and/or just an OS image you cant update.

These tft's are not very fast, due to low spi transfer rates and not optimized hardware and driver.
Have a look at what you can influence in SPI transfer rate in OS settings.This may help: https://www.raspberrypi.org/documentati ... /README.md

You get what you paid for: a cheap, functional but slow display.
I appreciate the response.. technically i didn't pay for it.. anyway, what brand and model of 3.5 screens would you recommend?

User avatar
hansotten
Posts: 322
Joined: Fri Jul 13, 2012 6:01 am
Contact: Website

Re: 3.5 tft lcd very laggy low frame rate

Thu Nov 29, 2018 2:36 pm

Pimoroni, Adafruit are known to support their products much longer than the Chinese.

Waveshare might be allright,

Though spi based tft's are not the fastest. HDMI is a better option, it works with any OS and version.

Just make sure there are instructions how to drive the tft in current Raspbian version (nowadays dbt device tree driven) and not just an OS image which keeps you stuck at that version.
http://duinorasp.hansotten.com for Raspberry Pi and Arduino and ESP8266
http://retro.hansotten.nl for retrocomputing with the 6502 cpu

juj
Posts: 30
Joined: Sat Nov 18, 2017 10:51 pm

Re: 3.5 tft lcd very laggy low frame rate

Wed Dec 12, 2018 11:53 pm

If you are able to identify the controller on the display, it may be possible to squeeze some more performance out of the display by using this driver: https://github.com/juj/fbcp-ili9341

User avatar
mwilliams03
Posts: 119
Joined: Mon Oct 29, 2012 2:56 pm
Contact: Website

Re: 3.5 tft lcd very laggy low frame rate

Thu Dec 13, 2018 4:58 am

Most of the these types TFTs use shift registers and ripple counters.
If you look at the back of you TFT, some of the chips should have 74hc4040 or 74hc4094. And these are only rate for about 20Mhz. These means the Pi SPI needs to be running at a low frequency for them to work. And therefore, low FPS

Our TFT (PiScreen )uses a CPLD which performs the same functions but can run at a much faster frequency.

We get +25FPS on our display, admittedly.. not as fast as a TFT or a DRM TFT... but it is cheap and very usable
Mark -- OzzMaker.com -- Creator of PiScreen - A 3.5" TFT for the Rasspberry Pi and BerryIMU.

Return to “Interfacing (DSI, CSI, I2C, etc.)”