home and limit

[Buechsenschuetz]

The switches mentioned in Jochen's Google search results are rather mechanical switches, mostly designed for motion systems with a certain power. We are using conventional micro switches, mostly with an extended lever and a roller at the tip - but these are prone to switch bouncing and need debouncing circuitry for proper operation of the 'find home' routine. We are also using slotted optical sensors (Gabellichtschranken in german), they are available from Omron and other suppliers. They have very precisely repeatable switching points and some come with a Schmitt trigger output which makes them even more reliable. We are using these opto switches (together with encoder feedback) for precision positioning for many years now.

[Buechsenschuetz]

You don't need analog i/o for limit/reference switches. Even if you would use (possible) analog i/o lines for detecting limit/reference switches this would not be a good solution since they are not monitored in real time. Also, due to software errors these signals may not be detected precisely.

There are dedicated inputs for limit/reference (home) switches on the 73x4 motion controllers, you should use only these for this purpose. You will need TTL level signals, you can also connect switches with open collector or mechanical contact outputs since pull-up resistors are provided. I would recommend wiring them such that they will give a valid limit switch output when the wire is broken, i.e. they should be 'active high'. You can select the active level (active high or low) by software. The output voltage of your switches must not exceed +5V, and their ground reference must be connected to digital ground of the 73x4 controllers.

[Gram]

Many thanks again for your detailed explaination.