2 Endstops per Input?

I am working on a corexy laser and don't trust my skills.

I would like to connect 2 endstops to each of the min and max inputs on ramps
Is it possible with current powered endstops or will I need to build my own unpowered endstops and connect them in series?

(Not sure how the powered endstops are designed)

If you use normally closed microswitches, you can connect two (or more) in series. The electronics will show the endstop as triggered if either switch is pressed. Powered endstops are a different matter. Some types can be connected in parallel, others can't. You need to tell us what type they are.

Edited 1 time(s). Last edit at 04/16/2017 04:38PM by dc42.

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Cheap Chinese optical endstops. I do belive that they could be following this schematic


If I read this correct, could I just connect the sig of the 2nd to the ground of the first to get the series link?

(+5 connected together, and then ground of the 2nd back to the ramps input.)

Edited 1 time(s). Last edit at 04/17/2017 03:09AM by GRAYWOLF.

I presume those work by interrupting the slotted opto switch when the carriage is at the limit, so the LED is normally on and goes off when the switch is triggered. Here are two ways of connecting two of those:

1. Connect the two outputs to the inputs of a 74HC02 nor-gate, then the output of the gate will go low if either switch is interrupted. For extra safety, connect a pullup resistor between each input of the gate and +5V, so that if you disconnect the opto switch then that input will register as triggered.

2. Hack the endstops to connect the two phototransistors in series.

Connecting the sig of the 2nd endstop assembly to the ground of the first won't work for two reasons. You need the IR emitters in both switches to be permanently powered, and the phototransistor on the first switch might not be able to sink the current needed to drive both indicator LEDs.

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Quote
dc42
I presume those work by interrupting the slotted opto switch when the carriage is at the limit, so the LED is normally on and goes off when the switch is triggered. Here are two ways of connecting two of those:

1. Connect the two outputs to the inputs of a 74HC02 nor-gate, then the output of the gate will go low if either switch is interrupted. For extra safety, connect a pullup resistor between each input of the gate and +5V, so that if you disconnect the opto switch then that input will register as triggered.

2. Hack the endstops to connect the two phototransistors in series.

Connecting the sig of the 2nd endstop assembly to the ground of the first won't work for two reasons. You need the IR emitters in both switches to be permanently powered, and the phototransistor on the first switch might not be able to sink the current needed to drive both indicator LEDs.

Thanks, looking at the way they are wired, I looks like it would but easer to make up little board with the gate on it.

"NOR" or "OR"?

Used to have some LS series chips, I wonder where I put them.

Sorry, forgotten my logic gates.

Edited 2 time(s). Last edit at 04/17/2017 06:11AM by GRAYWOLF.

Quote
GRAYWOLF
"NOR" or "OR"?

Either. NOR (e.g. 74xx02) will give you a low output when triggered, OR (e.g. 74xx32) will give you an active high output which is the same as your endstops do when you connect one directly.

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Ahh, so If I use the OR, I need to invert the input in code but If I use Nor, I don't need to change code setting.

Thanks, just need to work out how to make the PCB in Fritzing and how to order them.

Edited 1 time(s). Last edit at 04/18/2017 01:48AM by GRAYWOLF.

Other way round, if you use NOR then you need to invert the input sense. Better to use OR so that high means triggered, because endstop inputs are generally pulled high by pullup resistors when they are disconnected.

Adding a gate introduces another single point of failure, whereas using two microswitches connected in series doesn't.

Edited 1 time(s). Last edit at 04/18/2017 02:05AM by dc42.

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Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].