For those of you that are, how are you fixing your homing switches to the lowrider?
This seems like a perfect spot for this switch for the x-axis, how would you fasten this here?
Follow up question: would it matter, in regard to EMI, if I mounted a switch really close to a stepper? I mean right on it… A convenient place to mount the x switch might be to actually share a z motor mount screw.
Hot Glue?
Probably not. They have pull up resistors on the board, so it’s pretty tolerant to emi.
This is a LinuxCNC build, not sure about pullups. Switches and motors will be running on 24v.
You shouldn’t have a problem putting the limit switch directly on the motor. You had better have a pullup resistor one way or another – sometimes it’s internal to the CPU’s inputs. If the input is floating then you will have random triggering no matter what, whether it is near the motor or not.
Here is what the manual for my board says. I admit it’s a bit over my head. Little help re pullup/pulldown
"ISOLATED I/O
The 7I96 has 11 isolated inputs and 6 isolated outputs. All 11 Isolated inputs have
a common pin. This common pin must be connected to
ground for active high inputs and
connected to the I/O power for active low inputs. The 6 isolated outputs are completely
floating switches so can be use for pull-up/pull-down and mixed voltage switching.
ISOLATED INPUT CHARACTERISTICS
The isolated inputs use opto-isolators with a 4.7K
input series resistance. This
results in an approximate current draw of 5 mA at 24V. The inputs will operate with ±3V
to ±36V signals relative to input common. Isolated
inputs are relatively slow and not suited
for signals faster than about 5 KHz. For sinking type inputs, the input common pin is
grounded and a +3 to +36V signal is applied to the
input pins to activate the input. For
sourcing type inputs, the input common is connected
to +5 to +36V and the input pins are
grounded to activate an input.
"
My plan was just to wire the switches in parallel to the appropriate pins, I hadn’t thought of needing any resistors. +24v -> n.c. switch -> input pin and then gnd -> input common.
This will work.
For most inputs that are not isolated and don’t draw any current, opening the n.c. switch will leave the input in an indeterminate state. That indeterminate floating state is what the pull-up or pull-down resistor is needed to remedy. In your case your circuit will work as you’ve described.
1 Like