Flow Meter wiring

[ravsingh]

Hello,

Thanks Ray firstly for creating such an amazing device.

Question I have is regarding wiring a flow meter to the OSPi system, I’ve got a Nymet 3/4″ flow meter and couldn’t figure out the exact way to wire it to the ospi board. I don’t want to fry anything given I’ve only had it for a day.

Can you please share how you have done it?

[anke639]

I’m interested in this too, as I have the same flow meter. Although, given that it has three wires, I’m guessing it’s not a supported flow meter yet?

Will these flow meters perhaps be supported in the future?

[Ray]

If your flow sensor comes with 2 wires, most likely it’s supported. You can just wire it to the rain sensor terminal, and go to Edit Options -> Weather and Sensors to select the sensor type as ‘Flow’.

If the flow sensor comes with 3 wires, you will have to check the datasheet / spec to find out whether it needs to be powered, and what type of contact it provides. It’s still possible to get it to work with OpenSprinkler, but you will need to find out how the flow sensor works first.

Technically, the sensor terminal on OpenSprinkler is designed to connect to a ‘switch-type’ sensor. All rain sensors and dry contact flow sensors are such type of sensors — they are essentially rain-activated (or flow-activated) switches. The sensing pin is pulled high normally, so when the sensor switch is open, the sensing pin reads a digital high, and when the sensor switch is closed, the sensing pin reads a digital low. If your sensor outputs an digital/analog signal (and usually this means needs to be powered), it can still work as long as the output voltage is within limit (should be no more than 5V).

[anke639]

I have found the Technical Specifications for my flow sensor, which can be found at http://www.nymet.com.au/valves/1flowsensor.html

Flow Range: 2 – 100 LPM
Repeatability <= 1%
Accuracy <=2.5% of FULL SCALE
Max. fluid temperature: 60 DEG C
Max. Ambient Temp. Range: 0 DEG C – +60 DEG C
Max. Fluid Pressure: 1.5 Mpa
Operating Voltage: +5V – + 24V
Output Frequency: Square Wave

Would this be compatible with OpenSprinkler?

[Ray]

@anke639: this flow meter has 3 wires and requires 5V power. In order to get this to work, you will need to solder a wire from the OpenSprinkler circuit board (specifically the VIN pin) to provide the 5V. I would recommend you to find a different flow meter with two wires, which would not need to be powered.

[anke639]

Hi Ray,

Thanks for your help – do you have any models which are confirmed to work with the OS?

Thanks

[BinaryOS]

I have the same brand flow meter, 25mm version. I believe its 0.016067L/pulse from data I have (1 pulse/sec = 0.964LPM). The closest open sprinkler can be configured to is ether 0.01 or 0.02 L/pulse. Planning to fit an Arduino nano “in line” that will convert the (3 wire) pulses to a dry contact at say a 15:1 ratio so I can get the flow monitoring l/pulse setting closer. Just waiting on the relay module, the rest has been bench tested..

[Ray]

@anke639: you can find several suitable ones on Amazon, such as:
http://www.amazon.com/Dwyer%C2%AE-Multi-Jet-Pulsed-Output–C-03-1/dp/B00D2ME5MC
http://www.amazon.com/Water-Meter-Stainless-Steel-Output/dp/B00GM5DCCA
there are a lot of cheaper ones with 3 wires, but those typically use a Hall effect sensor which needs to be powered.

[Psykosonik]

Hi all is there any diagrams on the pinouts to power 3 wired sensors on the OS DC and eBay links to suitable sensors?

[ideasman69]

any reason why you couldn’t use 5v from one of the USB ports?

i was just about to purchase a flow sensor but will hold off until i can work out if the 3 wire ones work ok. they all seem to have a very high number of pulses/litre.

[george]

What if you put a 5v relay between the 3 wire sensor and the OS?

[Ryan]

I was going to start another topic but my query is along the same lines with a 5V pressure sensor instead of flow.

I’ve bought a 5V pressure sensor(http://www.ebay.com/itm/Pressure-transducer-or-sender-100-psi-stainless-steel-for-oil-fuel-air-water-/261260635816)

The A0 is providing 3.3V and I’m picking up 5V from VIN on the breakout at the side of OSPi.

I have a level shifter(https://www.adafruit.com/products/1875) in between OsPi and the pressure sensor.

The few things I am stuck on and cannot find any answers are:
* The above shifter is not i2c safe so does it make any difference as the A0 through A3 are only reading voltage and the PCF8591T is handling the i2c back to the Pi?
* The 5V from the VIN is reading about 4.798V would this affect the end result?

With no pressure(i.e. disconnected) I read 0.46V but when I apply some pressure the reading goes up accordingly so I hope its just a matter of calculating for the voltage difference.

If all of the above makes sense then would that level shifter also help the guys with flow sensor at 5V?

Many Thanks,
Ryan

[Ray]

For those who are interested in hooking up the 3-wire flow sensors to OpenSprinkler, I’ve just explained how to do so in this post:
https://opensprinkler.com/forums/topic/3-wire-flow-sensor/#post-41339
This is the same on both OpenSprinkler and OSPi. Basically, red wire -> 5V (VIN pin, also the 5V pin on the USB port); yellow wire -> rain sensor’s left port; black wire -> rain sensor’s right port.

Because there is a 4.7k series (protective) resistor between the sensor (which outputs up to 5V) and the digital input pin (which is only 3.3V tolerant), you don’t need a level shifter (most digital pins have internal zener diodes, which will clamp the voltage coupled with the series resistor).

The high pulse/liter count could be a concern as it may cause the number of clicks to exceed the software limit (but this can be lifted by changing a number in software). In general, I would advise against these type of cheap sensors as they are not very accurate or reliable.

[Ray]

@Ryan: the pressure sensor you referred to is an analog sensor, which is different from the flow sensors. Therefore you can only use the analog pins to interface with the pressure sensor, and not the rain sensor pin.

There are two possible solutions for level shifting. First, if you only care about readings between 0 to roughly 75psi, you can directly connect the sensor output to A0 without level shifting. This is because electrically I think PCF8591 can tolerate 5V (if unsure, you can connect a 1K resistor inline between the sensor and A0), it’s just that (according to the graph) beyond 75psi the output will rise above 3.3V hence will saturate the analog reading. If you don’t care about readings above 75psi, this should be fine.

The second solution is to use a resistor voltage divider that can create a 5 to 3.3 ratio, hence linearly scaling 5V down to 3.3V. For example, use a 1.7K and a 3.3K resistor to form the divider. You’d better use 1% resistors for accuracy.

Regarding the accuracy of 5V, it does affect the accuracy of the sensor reading. In practice, the error may be small enough to ignore. But if you really want to calibrate the accuracy, you can probably use A1 with a resistor voltage divider between 5V and GND. This way, you can use A1 reading to calculate the actual VIN voltage.

[avrahams]

Hi Ray,

I have a two wire flow sensor and your wrote to wire them to the rain-sensor terminal.
Do you mean to wire it to sn1 and sn2 or to wire it to sn1 and ground?
Thanks

[Ray]

@avrahams: from your description it sounds like you have OpenSprinkler 3.0. Wire it to SN1 and GND (ground).

[Author]

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