#Opto isolator board with led software#

Luckily, these boards have a more robust 12V rail from which to feed the switches, although it is still returned to the common 0V on the board. To increase resilience to noise, people add opto-isolators, although they usually still power the long sensing loops from the 5V logic rail adding another route for transients into the control pcb. This is not a fail-safe arrangement as the scheme will not work if a switch wire breaks or disconnects.Ī safer arrangement (although vulnerable to short circuits) is to use normally-closed switches and wire them in series so the circuit breaks when an end stop is hit.

#Opto isolator board with led software#

If either of them closes through physical contact, they pull the pin down, and the MCU software stops the machine. The arrangement used (I can see there should be a diagram here…) is that the two end stops on each axis are normally-open and wired in parallel. These transients can run up the signal wires or the ground wire into the board. On the board, those end stop connectors are wired straight to the pins of the ATmega (its internal pull-ups are enabled), sometimes with a capacitor to eat spikes, and the software has a delay to try to help with false triggering.Įven so, the long wires are prone to pick up transients from the (usually) unsuppressed spindle motor as well as the steppers motor drive wires.