Limit switch pull-up?
Posted: Sat Mar 05, 2022 7:37 am
Hi,
I'm, having some issues getting my limit switches to work correctly for my custom machine. I have PNP NO inductive proximity switches in both directions (min and max) on all three axes. They are supplied by +24V and share ground with the buildbotics controller which I bought a few weeks back. I read in the latest manual that the limit switch inputs can go up to 50V without damaging the controller so these switches are NO with 0V for not engaged and +24V for activated.
Now, the problem is that there seems to be some voltage offset somewhere that makes the output of my limit switches be at around 0.8 V when they are not activated/engaged and this is above the logic voltage level threshold for this type of input according to the buildbotics manual v1.1.
Also, when I measure the voltage between ground and the motor # max/min pin without any switch connected I measure 3.2 V, which leads me to belive these inputs are pulled-up by the controller? SInce the inputs are pulled up: Is this set by the microcontroller or the raspberry or are there soldered resistors on the controller PCB?
I see the point of having a pull-up resistor if a classic microwitch is used, but not really in any other situation..
Any insight would be very helpful.
Thx,
Adrian
I'm, having some issues getting my limit switches to work correctly for my custom machine. I have PNP NO inductive proximity switches in both directions (min and max) on all three axes. They are supplied by +24V and share ground with the buildbotics controller which I bought a few weeks back. I read in the latest manual that the limit switch inputs can go up to 50V without damaging the controller so these switches are NO with 0V for not engaged and +24V for activated.
Now, the problem is that there seems to be some voltage offset somewhere that makes the output of my limit switches be at around 0.8 V when they are not activated/engaged and this is above the logic voltage level threshold for this type of input according to the buildbotics manual v1.1.
Also, when I measure the voltage between ground and the motor # max/min pin without any switch connected I measure 3.2 V, which leads me to belive these inputs are pulled-up by the controller? SInce the inputs are pulled up: Is this set by the microcontroller or the raspberry or are there soldered resistors on the controller PCB?
I see the point of having a pull-up resistor if a classic microwitch is used, but not really in any other situation..
Any insight would be very helpful.
Thx,
Adrian