Getting a LJ12A3-4-Z/BX-5V NPN Pulse Counter to work

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bulthaup
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Joined: 29 Jul 2019, 15:10

Getting a LJ12A3-4-Z/BX-5V NPN Pulse Counter to work

#1 Post by bulthaup » 29 Jul 2019, 15:53

Hi all, this is my first post. I have been reading here for a while now to find cool projects to learn from in my home automation setup. I have very poor knowledge of electronics but I would like to learn more so please spare me if I made a rookie mistake :) Hopefully others will be able to learn too from this post.

I am trying to get a NPN sensor to work to measure a watermeter. I have followed instructions here:

https://espeasy.readthedocs.io/en/lates ... j12a3-page


I have bought the 5V version of this sensor and attached a separate DC power supply (5V/600mA) to the sensor. Normally the wiring is like this:

VCC (brown)
GND (blue)

If I connect the + wire from the DC power supply to the brown wire and the - wire to blue, the sensor doesn't work. Maybe a mistake in China? :) If I connect them the other way around, I can see the red LED blink when I hold a metal object before the NPN sensor. So far so good.

I am running a NodeMCU with Git Build mega-20190630 and I have configured the device as required. The black wire (signal) is connected to D6 of the NodeMCU. The NodeMCU is powered by USB via my computer for testing for now.


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The problem is that I'm not able to get any pulse registered whenever I hold a piece of metal in front of the NPN sensor. When I unplug the black wire from D6 sometimes a pulse is registered but not always. If I try this on D5, no pulse count is ever detected (even not when unplugging the signal wire).

When I measure the sensor it goes from +1.12V to -3.56V when I hold a piece of metal in front of it.

Any help would be much appreciated!

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