External Pulldown resistor question

Hello all,
I was wondering if I had to use a external pulldown resistor for each HFS-DC06 (4 total) or could I use (1) 10k resistor and tie the grounds together and signal out to D2 D3 D4 D5?

Board- Nano

Don't these things have open collector output? Use the built-in pull-up instead.

Anyway, of course you need one resistor per output.... otherwise you'd have to connect all outputs together (which in case of open collector will be fine, but in case of push-pull outputs can be pretty disastrous).

for each HFS-DC06

I don't know anything about that thing... Do you have a link to the specs?

In general, if you want them to operate independently they all need their own separate pull-up/pull down and their own input.

It doesn't make sense to wire them all together to one pull-down and then use 4 inputs.

But for example, if you have an alarm system with several sensors or switches you can wire them all together with one pull-up (or pull-down) into one input. That creates a "logical or" where any of the switches can trigger the alarm. But the processor can't know which switch/sensor was triggered.

If the device has push-pull outputs then wiring them together will not work, and may damage something.

e: External Pulldown resistor question
Thank you DVDdoug, wvmarle
I could not find anything on these as for pdf or a complete data sheet, I do need them to be separate as they need to tell me which side was detected. I will move to use 4 pulldown resistors one for each HFS-DC06 sensor. I was getting some false triggers and saw pullups and pulldown was the answer I needed but did not know if I could tie them together. Again thanks for your reply and have a great day.

This listing mentions 5V high output, suggesting push/pull. No external resistors needed. No word either on directionality of the things.

The moment you tie outputs together of course you can’t tell any more which one it is that is triggered.