This post will cover upgrading the Sunlu S8 printer. This S8 provides a lot of printer for the money. The S8 provides a 310 X 310 X 400 print volume for $170.
That is very cheap for the volume and an all metal printer. The S8 also comes with a very nice glass bed plate, filament sensor, and well packaged control box. The largest down side in my opinion is the lack of a bed probe. Manually leveling the bed off a z limit switch is very tedious and time consuming, not to mention less accurate than probing. I couldn't pass up the S8 when my ole A8 finally died after 10 years in heavy service and too many upgrades to count. I removed the 3Dtouch probe from my A8 and started researching the board on the S8 to get pin assignments so I could updated the firmware for a probe. I found several good sources of information but nothing comprehensive so I wanted to create this post to consolidate the information and document upgrades.
I will include links to download the firmware as well as pics of the technical documents below.
The Sunlu S8 board documented hear is the SH 2560_A4988 V1.01 . I located the pin diagram below which matches the factory board except it does not show the pin number for the extruder fan. I finally found out that it is pin 7.
The following image is the actual board with the hotend fan pin labeled.
I found and printed this BLtouch bracket for the S8 but had to mount it upside down from the orientation advertised in order for it to be at the right height. After install the probe z offset is -1.35mm.
I decided to use Marlin 1.1.9 as the base firmware and put a sketch together for the S8. The board to select in Marlin is the Ramps14_EFB and pins file pins_RAMPS.h. My first sketch included support for the BLtouch and some other features. I was able to upload it to the board using the Arduino IDE with no problems. The firmware worked fantastic for homing and bed leveling with the 3Dtouch but when I tried to run a print the printer would randomly pause for varying amounts of time through out the print. That was totally unacceptable. The issue turned out to be the baud rate and buffer settings. Once I corrected them the printer ran fantastic without any pausing. I was able to enable thermal-run-away protection, Linear Advance, and M600 when the filament sensor detects the end of the filament.
In order to eliminate the communication pauses and free up dynamic memory I had to disable SD card support. I print using Octoprint which is much more convenient. Lastly I added a "Kill" pin on servo pin 5 (D5). The kill pin can be used to control a relay for turning on and off the power to the heaters. That provides a redundant safety feature in case a mosfet or SSR were to fail closed. The BLtouch connects to pins (D11,5V,GND) and the Z axis positive end stop pins. The pic below shows the new connections to make. I had to connect the sensor pin with the white wire in toward the center of the board orientation, be careful when first using the probe, you may have to reverse the connector if it does not trip. To be safe try homing well above the bed and use your finger to trip the probe. If it does not detect then power off the printer and reverse the connection. So that covers the first upgrade which gives us a monster printer with probe and bed leveling capability for less than $200 delivered.
I will be upgrading the S8 to an all metal E3D V6 hot end, PT1000 hot end thermistor, and AC heater for the bed. I will update this post when I preform those mods and add another download for the associated firmware. The PT1000 thermistors are a no brainer upgrade that will allow temps up to 500c, well above the stock thermistors limit of 300c. The PT1000s get knocked for lower resolution but they have a plus or minus 0.7C resolution which is more than accurate enough for 3D printing. With all the upgrades done the S8 will be capable to print up to 400c at the hot end, a bed capable of 200c, bed leveling, and filament detection; all less than $300.