ANet A8 Rewiring for SKR V1.3 or V1.4

BigTreeTech SKR V1.3/1.4/Turbo vs ANet3D V1.5/1.7 Mainboard Connections

As these SKR and ANet boards perform the same basic function they have to have a similar set of IO (Input/Output) connections.  However, the physical location and orientation of the connectors is different and more problematic is that some connectors have different pinouts and/or sizes.  So connecting the cables is not a simple re-plugging exercise.

The schematics for the A8 and SKR mainboards can be found on GitHub:………/SKR-V1.3-SCH.pdf

My thanks to Paul Wood for pointing out some of the following basic wiring issues.

  1. LCD 2004
    Whilst the pinouts have not changed function, the voltage tolerance has.
    Warning: Do NOT use an unmodified ANET 5V Zonestar 2004 display with the SKR Board. The 5V on the switches will damage the 3.3V SKR boards ADC Input if not blow the entire chip.
    It can be modified but for the time and cost you should probably just buy a replacement. If you really want to use it then the hardware and firmware changes are discussed here.
  2. LCD 12864
    I do not have one to try this. But as the TFT 2.4 emulates the 12864 it should work.
    Note: The Ender 3 has wiring inverted compared to ANet, i.e. it needs different cables. So make sure you order your TFT 2.4 display with the ANet style cables.
  3. Bed Heater
    No Change, but I have installed an external MOSFET Board for the Bed Heater
  4. Extruder Heater
    On the SKR use the HE0 connector
  5. Fans
    Both Fan 1 (Print Cooler) and Fan 2 (Extruder Cooler) – must be rewired as the connections are crossed.
    Fan 1 (Print Cooler) is connected to the SKR CNC FAN connector, but compared to the A8 this has 12V & Ground reversed.
    Fan 2 (Extruder Cooler) is connected to the a generic 12/24V output connector next to the X Motor Connector.  This has the same pinouts as the CNC FAN Connector.
    I have added a “Low Voltage DC PWM Motor Speed Controller Module 1.8V 12V 2A” from eBay to the Fan 2 circuit to slow it down a bit and reduce the noise a lot, at the expense of a very slightly hotter extruder..
    3D Fan Wiring
    Note: If Fan 1 (Print Cooler) only operates at full speed, then you may also need to connect a 10uF to 100uF Capacitor to the +ve terminal.
  6. Thermistors must be rewired as the SKR uses a smaller 2 pin connector.
    Note: both of these are 100K Thermistors (i.e. not thermocouples) so it does not matter which way round you actually connect the wires. On SKR use the BED and HE0 connectors. The A8 uses 3 pin connectors and the SKR uses 2 pin connectors.
    3D Thermistor Wiring
    Note: The A8 Extruder Thermistor Sensor has 2 white wires.
    Note: See also my ANet Hardware page re: damaged Thermistors blowing up the SKR Board.
  7. X,Y,Z Endstops must be rewired.
    The A8 uses Pin1 Ground, Pin2 5V, Pin3 Sensor connected to a 10K Pull up to 5V with a normally open switch. The microswitch shorts Pins 1&3 when the endstop is reached.
    The SKR uses Pin1 5V, Pin2 Ground, Pin3 Sensor connected to a 10K Pull up to 3.3V
    Warning! Do not connect the ANet Endstops without rewiring to an SKR as shorting Pins 1&3 on the SKR would present 5V to the sensor pin on the 3.3V SKR ARM chip. Fortunately, SKR have added a 1K Resistor in series with the sensor connection but 5V could still potentially damage the 3.3V Processor chip.
    Update: The SKR 1.4 improves on this and adds 3.3V clamping circuitry to these pins so is actually protected.
    .3D Endstop Wiring
    If you are not worried about the proper color conventions (Black to Ground) then you can just move the red wire from Pin 1 to Pin 2 (center pin) otherwise move both!
  8. Stepper Drivers
    The SKR supports the RepRap standard StepStick Driver Board format.  But also has the additional jumpers on the motherboard to use the Trinamic drivers in UART mode without further wiring.
    3D Stepper WiringYou will need to work out what jumpers you need for your configuration and make the matching firmware configuration changes.

     Remember to manually set the boards VRef first, before plugging in the motors.  Even if you are planning to use them in UART mode. Depending on your choice of Stepper Driver Board the driver software may need to be INVERTED. Otherwise the motor wiring should be compatible and not need rewiring.

Creating Wiring Tails

To simplify switching between the two boards rather than rewire the ANet cables I decided to create some crossover tails.  I purchased some Battery Connectors Pairs and heat shrink tubing on eBay for approximately £10 and soldered together a set of the x-over tails as needed.

  1. 10 SETS JST XH 2.5-3 Pin Battery Connector Plug Female & Male with 150MM Wire
  2. 10 PAIRS JST XH 2.5-2 PIN Battery Connector Plug Female & Male- 125MM UK

Note: A mix of the 2 pin plug and 3 pin sockets is needed for the Thermistors


Image1: SKR Wiring Tails for ANet A8 Endstops,  Thermistors, Fans