I have decided to upgrade my old CTC Chinese 3D printer during this Christmas time. I already performed this kind of upgrade some years ago, but I did not take any log of it, so now I’m back to square zero with some interesting and unpleasant discoveries.

note: I write this blog’s post weeks later, some passage may be missing or imprecise.

Prepare the platform.io tools.

Marlin¹ firmware is develop using Paltform.io² and to compile it you need to create a compatible environment. Following the documentation online I setup a Python venv and used pip to install the library

python3 -m venv ~/python3
source ~/python3/bin/activate
pip install platformio

Fetch and compile the firmware.

Clone the Marlin¹ firmware and the example configurations repository³.

git clone https://github.com/MarlinFirmware/Marlin.git
git clone https://github.com/MarlinFirmware/Configurations.git

Pick the version 2.1.2.1 with the configuration from CTC I3 example:

cd Marlin
git checkout 2.1.2.1
cp ../Marlin-Configurations/config/examples/CTC/i3 2560 Rev A/no probe/Configuration.h Marlin/

Patch the configuration to fix the bed type, which, in my case, is a 12V

diff --git a/config/examples/CTC/i3 2560 Rev A/no probe/Configuration.h b/config/examples/CTC/i3 2560 Rev A/no probe/Configuration.h
index fc22fdeb98..6905b10b16 100644
--- a/config/examples/CTC/i3 2560 Rev A/no probe/Configuration.h        
+++ b/config/examples/CTC/i3 2560 Rev A/no probe/Configuration.h        
@@ -753,11 +753,16 @@
   //#define MIN_BED_POWER 0
   //#define PID_BED_DEBUG // Print Bed PID debug data to the serial port.
 
+  // 12v (120 watt?) MK2a PCB Heatbed into 4mm borosilicate (Geeetech Prusa i3 Pro, Pro/B/C/X)
+  #define DEFAULT_bedKp 234.88
+  #define DEFAULT_bedKi 42.79
+  #define DEFAULT_bedKd 322.28
+
   // 120V 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)
   // from FOPDT model - kp=.39 Tp=405 Tdead=66, Tc set to 79.2, aggressive factor of .15 (vs .1, 1, 10)
-  #define DEFAULT_bedKp 10.00
-  #define DEFAULT_bedKi .023
-  #define DEFAULT_bedKd 305.4
+  //#define DEFAULT_bedKp 10.00
+  //#define DEFAULT_bedKi .023
+  //#define DEFAULT_bedKd 305.4
 
   // FIND YOUR OWN: "M303 E-1 C8 S90" to run autotune on the bed at 90 degreesC for 8 cycles.
 #endif // PIDTEMPBED

Compile

pio run

Upload the firmware.

to upload the firmware should be enough to

pio run --target upload --upload-port /dev/ttyUSB0

where /dev/ttyUSB0 is where the USB-connected printer appears (fix based on your system). It should work but it didn’t.

The unpleasant discovery

Try to understand what was wrong, after testing and re-compiling I decided to use an Atmel programmer to write the firmware or, better say, to rewrite the bootloader and then re-upload the firmware via USB. I was quite confident my problems were in the bootloader (spoiler alert: I was wrong).

Soon also I realized that the board does NOT have a plug to connect an external programmer!

Fortunately I found this picture showing, in the LCD panel’s connectors, where the required pins are located.

Also note that my connectors have been mounted upside-down!

Connected the programmer and run the AVRdude to check the MCU I received an error regarding wrong MCU type.

Ops… I have a CTC gt2560 board with an atmega1280 microcontroller instead of the atmega2560! And yes, a quick look with lenses at the chip on the board could have spare me an hour or so trying to upload a firmware compiled for a wrong MCU.

Fix the platformio and complete the job

Apply a patch on the palatform.io configuration file to fix the MCU type

diff --git a/platformio.ini b/platformio.ini
index 8b79ea2537..576a2b236a 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -13,7 +13,7 @@
 [platformio]
 src_dir      = Marlin
 boards_dir   = buildroot/share/PlatformIO/boards
-default_envs = mega2560
+default_envs = mega1280
 include_dir  = Marlin
 extra_configs =
     Marlin/config.ini
@@ -276,12 +276,13 @@ monitor_speed     = 250000
 monitor_eol       = LF
 monitor_echo      = yes
 monitor_filters   = colorize, time, send_on_enter
+#upload_protocol = atmelice_isp
 
 #
 # Just print the dependency tree
 #
 [env:include_tree]
 platform         = atmelavr
-board            = megaatmega2560
+board            = megaatmega1280
 build_flags      = -c -H -std=gnu++11 -Wall -Os -D__MARLIN_FIRMWARE__
 build_src_filter = +<src/MarlinCore.cpp>

compile and install did actually complete without errors.