DIY 3020 CNC I/O Board

[Pointy]

Hi guys,

I have a version of this circuit that works fine, but it is picking up 5v off the BOB and has no opto-isolation. Not ideal, so here is the redesign...


My thinking is as follows...(which may or may not be correct)

The circuit will do nothing until I throw the main controller switch, this will then feed the 24v into the LM2575 5v switching regulator and power the circuit.

Each input is active low and has a LED to show it's status, except OK1A, which feeds a flip flop driving a red & green LED. The green LED is lit when the Estop switch is disengaged but the red LED lights when the Estop switch is engaged.. The capacitors C1-C4 are supposed to help de-bounce any input switches, although I am not sure of the best value or if they do any good, I think I had 0.01uf on the previous board. I am also not sure if the 10k pull-up resistors are needed with the opto-isolators. I am currently using 1 input for a probe, and 2 for Home/Limit switches, which leaves one spare.

The first output (pin14) controls the spindle. The 556 timer is used for a 5 second delay and 5 second buzzer warning. MY CNC controller (3020 Tonsen variant) has a separate spindle control which is fed by 240v, the actual switching on is controlled by grounding a signal cable, so there is no mains voltage near the circuit. The other 2 outputs are spare.

I wasn't quite sure of the best values for the resistors R23-R27 & R28-R30, I stole the values from the G540 schematic. If anyone can see any obvious glaring mistakes or can suggest a better way of doing something, please feel free to comment. After all I am just a novice at this.

Regards,

Les