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Monitoring residential water usage by reading municipal water meter with Hall effect sensor + Arduino

Picture of Monitoring residential water usage by reading municipal water meter with Hall effect sensor + Arduino
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If you'd like to monitor your water usage, as part of a DIY smart home automation and monitoring project, then this instructable might help you to achieve that goal. The solution described here is non-invasive, uses your existing municipal water meter, and the total project cost can be kept under $5-10.

First, let's take a look at what is going on inside a typical residential water meter. The most common water meter type that is installed by local municipalities is a positive displacement water meter. This type of water meter design usually incorporates a wheel, as part of the internal mechanism, with one or more magnets attached to the wheel. When water is flowing through the meter, this wheel spins, driving the register. The register is the part that sits on top of the water meter, analog or digital, that shows you how many gallons of water you have used.

This magnetic drive between the water meter and the register is used in virtually all residential water meters. So to measure water flow, you just need to monitor whether this wheel is spinning, and how fast. Since the wheel has magnets attached to it, the magnetic field from the magnets will almost certainly be detectable from the outside of the water meter enclosure.  To test this, hold a compass next to the water meter. Hold it close to where the meter and the register join, this is where the magnetic field will be strongest. If the compass needle fluctuates when the water is flowing, then there is a very good chance that you will be able to monitor those fluctuations.
 
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fstr2 months ago

The instructions and schematics are a bit over my head so I bought a sensor module from eBay. But it appears the sensor is not strong enough to read my water meter. It's range is 7mm to 10mm depending on the magnet strength. I tested it with a strong magnet and appears to slightly exceed the 10mm claim even.

Is it possible to boost the signal from the sensor?

The module in question is here:

http://m.ebay.com/itm?itemId=230955026196

Water meter is a Sensus SR-II/SR-A

drewzarn2 months ago

Your schematic shows the lm324 with ground to pin 4 and +5 to pin 8. However, the pinout of my lm324 shows pin 4 as vcc and pin 11 as ground (pin 8 is output for internal amp 3). Seeing as I have no idea how an op amp works, why the difference? Thanks!!

titusjon3 months ago

Can you explain the difference between the circuit diagram you uploaded a few days ago and the one that was up here originally? I don't think the text description matches the new diagram, so it's a bit confusing.

Gregory0 (author)  titusjon3 months ago

I've updated the amplification circuit to a much better design. Let me know if the description is clear enough. I'll add some more details in the near future.

You've completely missed concentrating the field with pole pieces. You can get 100X more signal that way.

Can you explain this a little more?

Imagine the shape of the field around the magnet inside the meter, it flows from the north to the south pole of the magnet. Your job is to intercept and concentrate that field, which is probably oriented towards the meter on the front, and not out to the side

Putting a piece of transformer iron on the back of the sensor, and iron concentrates the field from the magnet. A lot of experimenting is needed for the best result though - maybe putting the magnet, and "pole piece" on the FRONT of the meter would help too.

Imagine the shape of the field around the magnet inside the meter, it flows from the north to the south pole of the magnet. Your job is to intercept and concentrate that field, which is probably oriented towards the meter on the front, and not out to the side

Putting a piece of transformer iron on the back of the sensor, and iron concentrates the field from the magnet. A lot of experimenting is needed for the best result though - maybe putting the magnet, and "pole piece" on the FRONT of the meter would help too.

huckw10 months ago
So I adjust R3 while monitoring the voltage between R4 and R5 until its just a little bit below the quiesent voltage of the sensor correct? And I measure the quiesent voltage of the sensor between the sensor and R2?
kevinmp331 year ago
How many voltage did you use to supply the LM124?
Gregory0 (author)  kevinmp331 year ago
Both the op-amp and the hall effect sensor are powered by +5v from an Arduino, which in turn itself is powered by USB.
great idea! has this affected your water usage?
Gregory0 (author)  amandaghassaei1 year ago
Not really, since the marginal cost is around $0.0005 per gallon. Having an alert when there is a small leak, or something that has been left on too long (like a forgotten sprinkler), is the most useful feature.
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