CNC Improvement 6. - Parts removed

During the weekend I removed all unnecessary things from the box of the controller.
This was it look like originally:

This is after removal of the parts:

The removed parts:

Yes you see it right. I thrown away the whole control electronics of the spindle. It looks like that is impossible to me to use this as part of a closed loop control.
As a for the first step the spindle will run on it's full speed.
This is what I done already:

Here is the last missing part:

Everything assembled together:

The second step will be, to drive a MOSFET from that one of the controller board's relay output and this will switch the spindle on and off. In this place I would use an SSR, but I had very bad experience with the DC ones in my 3D printer (due the working theory just a BJT can be used effectively in it, and the BJT has to high voltage drop for this type of high current driving). This only solve the switching and not the rotational speed control from the LinuxCNC.
The third step will be the closed loop controller. To be able to implement it the spindle have to get an equipment for rotational speed measurement. This is planed to solve with the exchange of the plastic rotor and an optocoupler. The controller itself will be an MCU based PID controller with rotational speed display. The setting of the rotational speed will come from LinuxCNC. The LinuxCNC has a low frequency (10Hz) PWM output possibility. I'll measure the pulse width of this PWM, and set the motor controller to it in big steps (100-500 rpm, what I haven't decided yet). I need the big steps, that the accuracy of the measurement do not cause the instability of the control.