Eh! What?

  • I recently purchased the BB-CAPE-DISP-CT43BB-CAPE-DISP-CT43 for my Seeed Studio Beaglebone Green.
  • I'm pretty familiar with bare metal, but I want to do a modern GUI for an instrument I am building.
  • Linux seems to offer a way forward with good GUI capabilities
  • The Beaglebone with the TI Sitara is quite transferrable to a new PCB design with other components.
  • The BB-CAPE-DISP-CT43BB-CAPE-DISP-CT43 looked like a good way to put an LCD display on the Beaglebone for a bit of a software lash-up.

 

Summary

  • It works. It's cheap. I like it.
  • There were some problems.
  • I've written about the problems here because I wish someone else had told me.

 

I'm not kidding

Beaglebone Green with 4.3" TFT Touchscreen Display running Debian 10.3 IOT and LXDE

Look! there it is, it works.

 

The Problems

  • When I was buying it, I was never too sure if it would work with the Beaglebone Green.

The Farnell page says "for Beaglebone Black". Beaglebone black has an HDMI interface and framer. I don't know how that works but I do know that the Beaglebone Green does not have an HDMI framer.

I wasn't sure if the LCD would need it, but I guessed it would connect to the LCD port which is physically a part of the TI Sitara microprocessor.

Luckily I was right. This cape works happily with Beaglebone Green.

 

  • I wasn't too sure how to make the LCD interface work in the Linux environment.

The Farnell page refers to a pretty flimsy data sheet.

Frankly it's not very encouraging, it doesn't even show the display with any software running on it.

They offer a readme saying that some aspects of the board aren't really supported yet.

It looks a bit shonky form a software perspective.

 

Actually it's all fine. You don't need any software from Farnell at all.

All you need to do is load the most recent IOT SD card image from the Beaglebone site.

 

At the time of writing the latest image is "AM3358 Debian 10.3 2020-04-06 4GB SD IoT".

You can download it here

 

Graphics on the LCD is inherently supported. The machine will boot to a text mode console on the graphical LCD display.

If you want a Linux desktop just install one. You will get a login dialog box and then a graphical desktop.

 

You can find instructions for the LXDE install here

Use the instructions for LXDE on Debian Wheezy the other instructions might work too - I didn't try those

 

  • There are no schematics for the board.

There is barely anything on the board, so you might think you don't need one.

Actually you don't really know what's happening there, and if it doesn't work you're left guessing.

It's pretty lamentable that there are no schematics available, it encroaches on Raspberry Pi territory.

It's hardly an NDA thing, it's just a boost regulator and an EEPROM, after all.

 

  • I was unlucky. Out of the box mine had an electrical fault.

Not knowing the previous three things I lost a lot of time to research. I was trying to figure out why the software was wrong.

Actually, it wasn't until I inspected the LCD electrical signals I realised that the 10MHz LCD clock was not right.

On my oscilloscope I could see the signal was stuck high and "all spikey like".

Using a multi-meter I was able to identify that the the clock signal was shorted to the 3.3V rail.

Careful visual inspection revealed a short on the LCD flex connector. Picture below;

 

LCD Flex Connector Short

 

The basic design of the board is not well thought out. I can see already that the failure rate on these boards is going to be high and that they cannot easily be tested.

Testing would have been possible but not at the price the board is sold at.

I suggest that it is quite likely that other people will see failures on these boards too.

 

If you get a board with a fault like this Farnell are very good about returns. I decided to fix mine.

In the picture below you can see the problem;

 

Display Cape Overview

 

The 0.1" pitch header is very close to the LCD flex connector. You can't easily get in with a soldering iron to clear the short.

I flooded the area with liquid flux. I have a Weller TCP iron with a screwdriver tip "Weller ETB". It's a pretty chunky iron, and you have to be careful not to melt the header.

I folded the end over on some solder wick and hooked it over the top of the connector. I applied the iron vertically to the board and pushed outwards against the wick and the connector.

It took a lot of attempts to catch and soak up the short. Be patient and use lots of flux. You can clear the short without melting the connector, even with a chunky iron.

 

Happy hacking.