Hi. I have just purchared this board and will be using a 3d touch probe. The probe has 3 wires, 24v+, 24v- and a signal wire to the pin 4 (I think). The way I see it is that the probe is NO and the si

I am assuming that you are referring to the Mach3 USB controller. Your understanding seems mostly correct, but it's important to clarify a few points regarding the 3D touch probe and the Mach3 USB Interface Board. The probe has three wires: 24V+, 24V-, and a signal wire. Here's how it typically works: 24V+ and 24V- Wires: These are for powering the probe. Make sure they are connected to the appropriate power supply. Signal Wire: This wire sends the signal to the board when the probe is activated. In your case, it seems to be connected to pin 4. Active Low Setting: If the probe is Normally Open (NO), when activated (i.e., when it touches the surface), it will complete the circuit. If you're using "active low NOT ticked," this means the board will interpret an open circuit (no contact) as an active signal. When the probe touches a surface and closes the circuit, the signal will stop. It's crucial to ensure that the probe's voltage specifications match what the Mach3 USB Interface Board can handle. Since the board's inputs might not be designed for a 24V signal, using a voltage divider or an appropriate interface circuit to step down the voltage to a safe level for the board might be necessary.