Estlcam defines pinouts for a controller. This board is for an Arduino Nano. Outpus (Spindle is 3 pin) go to 4pin 'Axis' connectors. Inputs (4) go to 2-pin plugs with pullups and caps. Analog 6 is output to a 3 pin connector
There is a connector for a HC-05 module. Tx and Rx Jumpers chose pin selection. D0-Rx-D3 and D1-Tx-D2 if using with USB port to monitor. (Beware D2 and D3 are used by Estlcam).
For NON ESTLCAM uses there is a I2C connector (uses A4 and A5)