[Move] Controlling 5vdc outputsfrom Mother PCB with Arduino MEGA 2560 or Raspberry Pi

I need some basic help. I am working with an older CNC machine controlled by a PCB (which controls 24vdc step motors). I wish to use an Arduino or Pi to control this from my computer interface (i.e., digitally)

I have 7 lines from the MASTER PCB that need to go to the ARDUINO to control everything.

Line 1 - Ready analog voltage READY LINE. Once we power up the CNC PCB and it does a physical initiation this line goes from 0 to .75vdc and allows then

LIne 2 to go to 5VDC- CREDIT/TIME ADDED LINE-If this line then goes to ground then it pulses the MASTER PCB and adds time and credits (Its a simplified circuit for this explaination). Once CREDITS (for lack of a better word) are pulsed by grounding the pin, credits are added and allows.

Line 3-7 to go to 5VDC contstant. These 5 lines used to be attached to an actual joystick with limit switches. Grounding any one of them results in the cutting head moving in whatever 4 directions you desire. The 5th line when grounded from it's 5vdc contant voltage starts the cutting head.

I had started with these 7 pins in the PWM headers 3-9pin positions on my MEGA 2560 but found that WHEN ARDUINO IS POWERED UP THESE PWM PINS ARE ACTUALLY DEFAULTED TO GROUND and I have blown up another MASTER PCB. I actually need these 7 pins to be DEAD and NOT grounded at all to anything until I need it. Only when I want to switch them to ground via my software.

Do I need a relay breakout board? Can I do this with programming the microcontroller itself? I really need some detailed guidance despite my lack of IC's.

Arduino MEGA Control of MASTER PCB wth 5vdc contant

I have outputs from a master PCB that are primarily 5VDC. They are constant ON 5VDC and grounding them to 0 is what controls the stepper motors. I wish to hook them to an Arduino MEGA 2560 and control via computer interface but the default to the PWM pins are GROUND. I need them to be dead until switched to ground via software.

What do I need to do hardware or software wise to get these to be DEAD at the pins upon ARDUINO power up, Can I use GPO pins or analog input pins?

Relay board? My problem is that i am controlling an existing motherboard that had previously used limit switches 5vdc/grnd as it's signal. I have 7 lines from the master PCB. 1 is the ready analog signal that goes from 0 to .75vdc when board is ready.

Other 6 are credit/time pulse switch and 4 way movement and start cutting head. Any suggestions are appreciated.