Unconnected cable sending flow data

[Marco83]

Hello, I have an issue with my flow sensor.
The unit has been working fine for one year or so, set at 0,01 L/pulse; then it started showing an uncommanded 10.00 L/min flow even when water was actually not flowing.
Suspecting a faulty flow sensor, I disconnected the flow sensor from its end of the 15 meter cable running from the Opensprinkler unit to the flow sensor, leaving the other end of the cable connected to the Opensprinkler unit; however, the 10.00 L/min flow remained.
Suspecting then a faulty Opensprinkler unit, I disconnected the other end of the 15 meter cable from the unit, and the flow stopped immediately.

It looks then like the unconnected cable is sending pulse to the Opensprinkler! The rate is 10.00 L/min at 0,01 L/pulse, so 1.000 pulse/min. This does not even match with the AC frequency running the valves (which anyway are normally closed and unpowered most of the time), as 1.000 pulse/min is 17 Hz, and the AC is 50 Hz.

What the hell is going on?

Thanks a lot!

[ShawnHarte]

Is your sensor positive or negative pulse? If you have a bad sensor and leave the sensor wire “floating” all sorts of wierd things can happen. The wire acts as an antenna and once the voltage on the wire reaches a high enough peak it will trigger a signal. The wire can get interference from just about anything, like wireless routers, your TV, the microwave, or even radio stations. So trying to tie the phantom pulse to something can be very difficult, however, it is likely you have a bad sensor and replacing it will remedy the problem.

If it’s a positive pulse setup don’t ever leave the wire hanging in the air with nothing attached, a large enough charge can build on the wire and damage the port. This is why cable TV ports left open will have terminators, a basic load, on them.

If you have a negative pulse setup, watch for bad or disconnected grounds. A partial ground fault can cause spurious signals. Leaving the wire hanging in this setup usually results in bad or no data, but can damage the port sending the signal down the wire by acting as a short circuit. Odds are this is the type of sensor you have and it is either bad or the wire going to it is damaged or improperly connected.

Short answer, you most likely need to replace your flow sensor and the problem will go away. Hope that helps a bit.

[Ray]

I want to echo SharnHarte that perhaps you are getting some sort of signal interference. The sensor uses ‘interrupts’ to detect flow pulses. If the wire is sending pulses unexpectedly due to signal interference, that could be interpreted as flow pulses.

When you leave only one cable in the sensor, you should try both ports of the rain sensor: one of the port is circuit ground (I think it’s the one on the right). I assume if the wire is left in that port it shouldn’t have any interference since that’s the circuit ground. You may have left the wire in the other port (which feeds into a microcontroller pin) and that is prone to interference from ‘floating’ signals.

[Marco83]

Thanks everyone!
I believe it’s really an interference, as is still keeps sending the signal even with the flow sensor disconnected!
How can I get rid of it?

Thanks!!

[Ray]

This sounds almost too mysterious to me: on the microcontroller, the pins for sensor inputs have internal pullup resistor turned on in the firmware, if this was caused by interference, it’s gotta be really strong interference that can overpower the pullup resistor. I can’t imagine how this could happen.

What if you change the sensor type to ‘Rain Sensor’ — do you just get randomly flipped rain sensor status? If os, I suggest that you send a support ticket and arrange for it to be sent back to us so we can check what’s going on.

[Marco83]

Hello, the uncommanded input did not stop after disconnecting the sensor from the cable (!) so I trust this is an interference matter.
Is there any way to eliminate it? I don’t know its source.

Thanks!

[Ray]

I asked you to change the sensor type to Rain Sensor, and see if it gets randomly flipped rain status. Did you try that?

[Marco83]

Sorry for big delay!
If I change the sensor type to rain, nothing happens if the “normally open” box is NOT checked, but it will say “rain detected” of the box is checked. What does it mean? Thanks!

[Ray]

What you observe is correct: when the sensor type is set to rain, you can choose between whether it’s a normally open rain sensor, or normally closed. Normally open means the sensor switch is open at resting state, and regarded as active if it’s closed. The normally closed option means the reverse.

[jaycan]

Hi,

I am experiencing exactly the same issue. Just wondering if there was solution to this.
My setup is as follows; OS 3.0, DC version purchased about 6 months ago. Flow meter is a new (quality) device purchased at the same time. It registers 1 pulse per 10 litres and connected with shielded cable. Flow was reading accurately up until a few months after installation. Readings are now ridiculously high , i.e thousands of l/min when the system is in idle and when in use. Flow meter cable has since been removed from controller and flow is still registering flow albeit much lower i.e. range 0-300 l/min.
Just wondering how this issue was resolved with Marco83.?

[Johann Vanackere]

Hi,

This thread is already old, but as I had the same problem with floating voltage on flow meter and I managed to fix it, here is what I did.

The SN1 input is supposed to have a pull-up resistor that should prevent noise on the wire when the flow meter is in opened state.
But after reviewing the hardware design files (https://github.com/OpenSprinkler/OpenSprinkler-Hardware/tree/master/OS/3.0/AC_driver) and opening my own OpenSprinkler device, it seems the resistor is just wired in-line, and not as a pull-up resistor (that should be wired between 5V and SN1).
So I simply added a 4.7kOhms resistor between 5V and SN1, everything works perfectly now. Higher resistor values might work as well, it depends on the level of noise you have on your wires.

Do this at your own risk 😉

Attachments:

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   Capture-decran-2023-08-13-221021.png
   

[Ray]

The wire-in resistor is for current limiting — believe it or not, we’ve had customers who mistakenly plugged in 24VAC to the sensor port, without a current limiting resistor, it will burn out the microcontroller.

There is no external pull-up resistor because the microcontroller has built-in pull-up resistor that can be turned on in firmware, which is exactly what the firmware does during initialization:
https://github.com/OpenSprinkler/OpenSprinkler-Firmware/blob/master/OpenSprinkler.cpp#L840

[Johann Vanackere]

Hi Ray,

I totally forgot about the internal esp pull up resistor, have been tricked by the inline one, thanks for the explanations 👍

Anyway, internal pull up was not enough for my situation (25m of unshielded cable, who runs along other 220v cables) and adding another one as described makes it work as expected, no more floating voltage on SN1 input.

Is there any way to ensure the internal pull up is actually enabled and mesure it’s value ?

Thx

[Ray]

The internal pull-up is relatively high, probably somewhere around 100K ohm. I didn’t know it wasn’t sufficient for some cases. Can certainly add a strong pull-up in the future version,.

The internal pull-up is always on — the firmware turns it on right at the initialization step. You can verify this by checking the sensor port to ground voltage (assuming no sensor is connected to interfere with it). The voltage should be around 3.3V, if so that means the internal pullup is on.

[Author]

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