Wow, @tgauchat…can you do that research a little faster next time? My hair wasn’t blown enough when you flew by.
So a little more detail for you guys. This will be to monitor my pool filter pressure. I am a new pool owner and it seems like the pressure at the filter is something that you need to know in order to know when to backwash, check the pump, or check the pool water level.
My requirements for the sensor are 0 - 50/100psi (doesn’t matter), +/-1% accuracy or better, 1/4 - 18 NPT port, and as low of an input current as possible - I would like to run this off of a battery if at all possible. I want to minimize cost as well, but will pay for a decent sensor from Honeywell, Measurement Specialists, etc.
Would I need the analog to digital converter if the Arduino can handle analog?
There are a bunch of these used in industrial applications, everything from air pressure to oilfields, but all the ones I know of are zigbee, not zwave. (Zigbee is typically better for outdoor use.)
Is there a reason you specified zwave?
Just to keep it in line with the rest of my home automation equipment. My pump is about 2 feet off the side of my house, so there is no range issue. I guess I could always buy the SmartThings controller to replace my vera.
Nope … Except that the A/D conversion of an Arduino may not be sufficiently accurate… then again, this paper implies it’s accurate if given stable input voltages, etc… Hmmm…
The ATMEGA chip used on the Arduino has analog inputs that can be used to accurately measure voltage
The Arduino microcontroller is provided with a successive approximation type Analog to Digital converter (ADC) which has the following specification. References shown in brackets thus (2: 26.1) refer to sections of the AtMega 2560 data sheet.
Resolution 10-bits (i.e. 00 0000 00000 to 11 1111 1111 binary, or 0 - 1023 decimal)
Integral Non-linearity • 1 LSB
Absolute Accuracy ± 2 LSB
Conversion Time 13 - 260 µs
Input resistance Rain =100M (2: 31.8)
Input resistance of Reference voltage Rref = 32k (2: 31.8)
These specifications tell us the Arduino is capable of measuring voltages to an accuracy
of ± 2 LSB - so the maximum error is 2 bits (4 decimal) in 10 bits (1024 decimal)
So the accuracy of the converter is 4 / 1024 or 1 part in 256 i.e. 0.25%.
However the limit of the measurement accuracy depends on the voltage reference used.
The Arduino has its own voltage references - but they are not very precise
Well, if you don’t have smartthings now, I wouldn’t add it just to get one sensor.
Pools are a bear, though. The chlorinated water is hard on everything that isn’t purpose built.
But here are a few more ideas.
Pardon the rapid posting, but I like shopping …
A quick search finds actual Digital Pressure Gauges for ~100psi to be in the $400+ range, and perhaps double or triple for wireless.
But even this high-pressure sensor itself is $265!
Or this, etc.:
I guess the questions remain:
Can “one-off” pressure-voltage sensor part be found with NPT connection and sufficient range, so that Arduino project could be built? Honeywell, etc., etc., manufacture this component. And lots of sources in China. Just hard to clearly understand the specs. There are lots of digital sensors with ICs, but I think these are mostly for low-pressure use (barometric, altimeter).
Can a non-wireless digital gauge be found for a reasonable price (? $100, $400 ?) that can be converted to wireless?
Normally I would say look at vehicle parts, which are typically smaller and cheaper because the max ranges are smaller, but…a pool. Most of the stuff you’re looking at won’t survive chlorinated water exposure.
Look instead at Jandy or one of their competitors. See the link I posted above.
I don’t think the board pressure sensors are going to hold up well to being exposed to chlorinated water, so one of the industrial types (Honeywell PX2 line or similar will have to be used). I could always put a tee on the valve coming out of the filter, put an analog gauge on one end, and the sensor/wireless transmitter on the other.
So… perhaps this…?
Catalog link: http://www.mouser.com/catalog/catalogusd/647/2209.pdf
Right… so a MIMOlite would do the job of both A/D conversion and Z-Wave transmission of the result; but no local “LCD Readout” in that type of configuration. The advantage of a custom built Arduino base, is that the embedded software and cheap add-on hardware can be customized with a display function and more.
There aren’t many generalized Z-Wave add-on boards, though, because of Z-Wave licensing requirements (?).
I could be ok with zigbee. I had been considering getting a smartthings controller anyhow.
So the cheapest route is to utilize an analog gauge with a tee for local and use a MIMOlite to handle the wireless. The most customizable route is to use an ardunio with zigbee for wireless and an LCD for local?
I am hoping, with either route, I can keep the box small enough to mount right onto the valve of the filter and not have to run a tube over to the side of the house to mount it.
Looks like these are the ones I’m looking for:
Looks like the Honeywell is about 3" total length and the MS is about 2.2". That might be the difference maker right there. Not sure why they are ~$30 more. Differences are 1/4 - 18 NPT pressure port, cable lead electrical connector, and 100psi max.
I think you’re right… Direct mounting should be possible with either solution.
The Arduino route has the advantage in form factor, as there are a lot of Arduino clones of various sizes, and it is “easy enough” to even build one from scratch with just an Atmel chip and the minimum oscillator and power regulator bits.
The Spark Core is Arduino with cloud-connected WiFi on same chip & board. It may consume more power and have other range issues though.
The unknown with respect to MIMOlite is whether or not any sort of dynamic calibration algorithm is needed for the pressure module (based on temperature, voltage regulation?). Again, the Arduino software can be written to do some calibration adjustments.
I’d recommend using the tee with analog guage for both calibration and backup.
Would I want to include a temp sensor so that adjustments can be made based on that input?
Temperature sensors, humidity, barometric pressure, etc. are all really cheap and easy to add to an Arduino project.
I think the biggest concern for accuracy is the voltage regulation, since that is what is driving the analog signal off the high-pressure guage.
First confirm the accuracy and calibration specs of the module itself. I presume output voltage is proportional to input × pressure.
Meanwhile we need to research what the is typical A/D accuracy of Arduino (or MIMOlite) and what folks add in software or hardware to optimize accuracy (e.g., perhaps they bypass the onboard voltage regulator for an external higher quality one, just a random guess). For super high accuracy readings, specialized chips are used that offload the A/D. These might even be quite cheap.
Anyhow… I’ll start some research.
Start with a local electrician. Codes for what can and can’t be added to swimming pool equipment, and even in the splash areas around a pool, can be very specific. Besides the obvious electrocution issues, there are also fire safety issues. (Two words: “galvanic corrosion.”)
I would also add that pool water and tap water are chemically distinct, and equipment rated for use in tap water pipes is not necessarily safety rated for a recirculating pool pump, for example.
There’s “Mr Wet Electric-Blanket” again
Yup … it’s up to @jc_cshmny (or the installer) to conform to codes. If I happen to build it, I won’t get it certified.
Definitely not worried about code for this one. The pump/filter also happens to be 20+ feet away from the closest edge of the pool.
It’s still a good idea to consider the safety issues, though.
The pump itself is recirculating the chemicalized water, it’s a secondary source. That’s what the filtration process is for, right? It’s not tap water. You can’t test water pressure without some part of the equipment being immersed. I’m just saying make sure it’s rated for swimming pools specifically, not just “water.”
One of the unusual things about pools is the method of chemical application. Basically you pour in a bunch of chlorine or a bunch of acid or a bunch of base and wait for it to circulate. Which means pockets of hyper whatever until it has circulated. and wildly varying values until it does.
All of that has to be taken into account in equipment design.