G-code over wifi

In the past I tried a Bluetooth link for sending g-code wirelessly to a 3D printer. It works ok but it seems a bit slow so eventually small stops happen while printing (buffer empties). Wifi was an expensive option at the time so I forgot about it.

Recently, the availability of the excellent ESP-link firmware together with NodeMCU/ESP12E boards for less than $5 painted a different scenario and while I was not on an immediate need of it I decided to give it a try during my summer holidays.

That firmware could be used with smaller and cheaper ESP8266 boards but I have found much more convenient to use (as they include their own voltage regulator) the so-called Nodemcu, just $1 more or so. These boards pack a 32bit SoC with 4Mbytes of flash and, lately, they are even supported through the Arduino IDE.

In order to keep the printer still usable through USB connected to a computer I patched Marlin so I could use an additional serial port for the wifi connection. The problem was that I already was using Serial2 for another purpose, so added code for simultaneously handling Serial3. Luckily the modification by TerawattIndustries showed how to add an additional serial port to be used for Bluetooth module. I had used that in the past to add an additional serial port to be used with some new G-code commands over an RS-485 link. This time I repeated the process with a twist, so now g-code is read from both Serial1 and Serial3 and responses are sent back to both ports too. This way no matter whether USB or wifi are the source of g-code the printer will work transparently.

Please note that ESP chip works at 3.3 volts while Arduino Mega works at 5V, so you do not want to connect an Arduino output to an ESP input as it can be destroyed by the excessive voltage. The opposite is no risk (applying 3.3volts to an Arduino input is not a problem and it will be detected as a high level).  You can see in the picture above the circuit and the two data connections (GND is connected if both boards are USB powered by the same computer or power adapter).  A simple 1N4148 (or similar) diode will be ok (as far as the RX input pin pull-up resistor is activated in the ESP chip).

In order not to mess with Marlin, I chose to use the alternate port configuration (RX2/TX2) on the Nodemcu so no boot-up strings would be sent when the wifi adapter is booting up. 

ESP-link configuration web based and I am pleasantly surprised on how well though out is done (the fact that the firmware tells you the new IP of the board once it has logged to another wifi network is just genius!!). 

Once you know the IP address of the wifi adapter (that now is connected to Marlin's Serial3 port) you can send g-code to it easily. Port 23 is the one used by default, but sending data cannot be done with command line tools like netcat as we need to have some flow control (i.e. not to send a new command if the previous one is not yet done). For each successful command, Marlin sends back an "ok" response. So I wrote a small program to send data to my wifi 3D printer.  

 Now I can chose to use the USB port or send data over wifi. More freedom to locate the printer not necessarily tied to a USB port.

UPDATE: I later found out that modern versions of Pronterface will accept an ip_address:port in the the serial com selector and it will then work using a socket connections instead of a serial port. So there is no need to use another program for doing that :-)