Hello!

I connect Pulse 15-Pulse water meter to GPIO RPi2 for tracking interrupts and water metering.

The counter is connected by one wire to GPIO, and the other to GND. For example, PIN29 and PIN30.

I debugged my C # script using the normal reset button removed from the PC case and everything worked correctly. When connected instead of a button counter, RPi behaves a trace. in the following way:

  1. If you connect to PIN29 and turn on the pull-up pull-up, the GPIO always fixes a logical 0. Even when the reed switch is open.

  2. If you connect to PIN5 (there is already a 1.8 kΩ pull-up resistor on this GPIO), then the GPIO always fixes a logical 1. Even when the reed switch of the counter is closed.

The key point, I think, is counter resistance. The multimeter captures ~ 1.6kΩ, of course, when the reed switch is closed.

How to make RPi track the status of the reed switch in the light of the above?

Resistance with closed reed switch enter image description here

    1 answer 1

    I will answer my own question.

    This system is called "Namur". It does not have an electrical open state in proper operation. In the closed and open state of the reed switch, the resistance changes. This is done to track 3 states at once:

    1) the reed switch is closed - resistance 1.6 kΩ

    2) Reed switch is not closed - resistance 5.6 kΩ

    3) The line is broken - resistance is infinite

    Making RPi work with Namur without opening the counter is not possible. The calculation of the system of equations showed that the parallel resistor must be simultaneously <1 kΩ and> 8.4 kΩ, which is impracticable.

    Ps changed counters and everything is fine now.