I posted this at the end of my long thread in the "DIY CNC Wood Routers", but maybe that isn't really the right forum. So here it is again - hoping for some comments:
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I've been doing some work on my controller card. But I wonder a bit, what inputs and outputs are useful?
The card will be set up and controlled via RS232. It will be run with step/dir signals from the parallell port.
In normal "run" mode it will listen for step/dir signals and encoder signals and make sure they agree by telling the motors how fast to spin. It will also monitor for positive and negative overtravel and disable the servos in case those signals are hit. It will send out error count over RS232 so that one can see how well the actual position coincides with commanded position, and it will map overtravel and home signals to the parallell port somehow - please help me out here to what's practical, I mean, there's four (five?) inputs on the port and three signals per axis that want out...
There will also be a "home" mode where one can home and reset the counters for the individual axes via commands over RS232. This mode will use limit switches and the encoder index pulse to find a reliable home for each axis. Will this be compatible with the different controller programs (i.e. is it possible to just zero their counter after an "external" homing has been performed?)
I will also put in a "set-up" mode that will hopefully help set the parameters for the PID controller - here the motors will be run open loop so that one can watch their step response.
So all in all, the inputs and outputs to the card will be:
* A, B, Z encoder inputs for each axis
* pos, neg overtravel inputs for each axis
* a home switch input for each axis (if one would like to home with the parallell port controller program without the aid of index pulses - or for Z maybe this could be used for a 0 plate?)
* +/-10V motor speed outputs for each axis
* One Servo Enable output that will be active as long as there is no fault condition (will be tripped by encoder errors, excessive position errors, overtravel - anything else? )
Sorry for another one of my long posts... and please comment! What would you be missing if this were your controller card?
Arvid