loading
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.

Step 1: Un-amplified and un-filtered Hall effect sensor output

To monitor magnetic field fluctuations you will need a Hall effect sensor. In my experiments I have used a Honeywell SS494B Hall effect sensor, which is available online for $3-$4. Other sensors should work also, just pick an analog model, not latching, with comparable or better sensitivity. The Honeywell SS494B promises to be sensitive enough to provide around 5mV per 1 gauss.  For a frame of reference,  the earth's natural magnetic field measures around 0.5 gauss, a refrigerator magnet is about 50 gauss, and a neodymium magnet is in the 1000's of gauss.

The Honeywell SS494B is a very sensitive Hall effect sensor, as far as low cost hall effect sensors go, but its measuring range still reaches over 400 gauss. Depending on the construction of your water meter enclosure, if it's made of  metal or plastic, the magnetic field strength outside the meter can be as low as 1 gauss or less. This presents a challenge, since 1 gauss or less is at the extreme low end of the Hall effect sensor's measuring range.

But before tackling the challenge of measuring very small magnetic fields, let's take a look at how the Honeywell SS494B Hall effect sensor works. The sensor has 3 pins: power (Vcc), ground, and output. If you were to look at the output from this Honewell Hall effect sensor, simply powered from a +5v source, you would see that the output sits at around +2.5v, or roughly half of Vcc. This is called the quiescent output voltage, or in other words, this is the voltage the Hall effect sensor will output when no magnetic field is present. But if you hold a magnet in front of the sensor, the magnetic field will pull the output voltage either towards ground(0V) or Vcc(5v), depending on the polarity of the magnetic field.

The tricky part comes next. If you were to measure field strengths of 1 gauss or less, the Honeywell SS494B will deviate no more than ~5mV from the quiescent output voltage. So, to use an Arduino to measure such tiny voltage fluctuations, and with good resolution,  amplification will be required.

To amplify the signal coming from the Hall effect sensor, a general purpose operational amplifier like the LM324 will work just fine. In my experiments I have used a widely available and cheap (less than $0.25) LM324 op-amp, and the schematic in the next step is based on the LM324 op-amp.

<p>As a meter seller, a couple FYI's. First, the drive magnets in meters vary in size by brand, and some brands are very small and may not be detectable outside the register shroud (Master Meter is very small). Second, some manufactures use 2 pole magnets and some use 4 pole magnets to better follow each other as shown below and reduce &quot;magnetic separation&quot; where they don't stay in sync. If you don't test, you might double or halve your output.</p>
<p>I'm interested in making this same sort of setup for my water meter and gas meter. I was curious about R2, R4, and R5. Why a 20K potentiometer for R2, but a simple 10K/10K voltage divider for R4 and R5?</p>
<p>is it possible to get a diagram that a noob like myself can follow. Unfortunately my concentration will not let me learn to well so I try following diagrams. The one that is posted here is most likely very simple but ya.....</p>
<p>I've built this circuit and followed the correct pin diagram, but something doesn't seem right. When I try to power it up, the LED on my 5V power source blinks (it should remain solid). Any thoughts of where I might be going wrong. I've checked the diagram against my wiring 3 times now and everything seems to be wired correctly. Any advice?</p>
<p>When did you come up with the idea?</p>
<p>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!!</p>
<p>Different manufacturers can have different pinouts for their products. Lesson learned: Always compare the schematic to the spec sheet of the IC chip used to make sure pinouts are correctly used! The Texas Instruments LM324AN had the same pins as you described, not as listed above. Spec Sheet for the one I obtained and used here: </p><p>http://www.ti.com/lit/ds/symlink/lm124-n.pdf</p>
<p>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. </p><p>Is it possible to boost the signal from the sensor? </p><p>The module in question is here:</p><p><a href="http://m.ebay.com/itm?itemId=230955026196" rel="nofollow">http://m.ebay.com/itm?itemId=230955026196</a></p><p>Water meter is a Sensus SR-II/SR-A</p>
<p>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.</p>
<p>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.</p>
You've completely missed concentrating the field with pole pieces. You can get 100X more signal that way.
<p>Can you explain this a little more?</p>
<p>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</p><p>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 &quot;pole piece&quot; on the FRONT of the meter would help too. </p>
<p>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</p><p>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 &quot;pole piece&quot; on the FRONT of the meter would help too. </p>
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?
How many voltage did you use to supply the LM124?
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?
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.

About This Instructable

86,244views

97favorites

License:

More by Gregory0:500W Halogen Work Light to 100W LED Work Light DIY Conversion (9000 lumens) Fixing Westinghouse LVM-37w1 LCD TV no turn on & shut off problem Removing infrared (IR) filter from Microsoft Lifecam Studio 
Add instructable to: