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Old 12-06-2012, 07:44 PM   #61
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- I rolled my own temperature sensors. I picked up some DS18B20s and some 'protection tubes' from http://www.brewershardware.com/Straight-Tubes/. I then used some binary thermal adhesive from Arctic Silver (http://www.arcticsilver.com/arctic_s...l_adhesive.htm) to seat the sensors in the end. Testing against a Spectrum industrial sensor I was 0.2 degrees off at 70 Celsius. Considering that is the error tolerance for the 'industrial' sensor at that point, it was good enough for me.
I'm trying to get the thermal capacitance and resistance down on my sensors for fast response time. In this regard I'll probably do the same thing with copper tubing.

For those not wanting to buy SS tubing on the Internet, a local hose and fitting shop that does custom work in SS will probably have lots of cut offs they will literally give away. AC and refrigeration shops work in copper and SS too, as do some instrumentation shops.

I am going to try to "pot" my sensors in the end of my tubing such that the sensor head is exposed directly to the liquid I'm measuring the temperature of. Stay tuned for more details as I test this concept.
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Old 12-06-2012, 10:18 PM   #62
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I'm trying to get the thermal capacitance and resistance down on my sensors for fast response time.
What dT/dt are you looking for? It would take me all of 5 minutes to put one in a pot of water and bring to decent temp and then drop another in to see how fast it rises to temperature. Obviously the larger the differential the greater the rate of change, and I think the temperature will be within a degree inside a second or two.

I offer because it was dead easy to make these probes and if you have access to a TIG/MIG and some time you could easily make the 'protection tubes' yourself. The material was pretty thin, so I don't think the usual copper versus stainless insulating argument is going to have much effect. I also think that attempting to get the sensor to touch the fluid directly is playing with fire and you could better use the time using that Zeus brewstand of yours.

-W

Thanks for pointing me towards the DS2408 BTW
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Old 12-06-2012, 11:09 PM   #63
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I'm real new to client/server stuff in Linux and just learning Python but I do recall seeing info on epoll and plan to see how that works since I have the gauges files, I have 4 sensors working on the w1 kernel module, and I have python code to pull and trim the sensor values. I actually connected a wire from my Arduino sensor buss (data) to GPIO4 so I am simultaneously reading the sensors on both setups.

Now if I can get this epoll feeding the Gauges js script I'll be somewhere.

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Old 12-07-2012, 01:57 PM   #64
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helibrewer, don't get tangled up in AsyncIO/epoll just yet. It is very much a nice to have. Given that the rPi is probably going to be dedicated to the brewing/displaying there is little value in using epoll to free up the CPU for some additional cycles.

That said, I've done a few tours of building python web applications, so if you have your code in a public repo somewhere I can help you out.

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Old 12-07-2012, 06:12 PM   #65
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Really like this idea. I don't have much experience with Linux but just ordered my Raspberry Pi. I had kind of been looking for an excuse to get one anyway. Right now I'm wondering if I would be better to get a 1 Wire adapter or just use the onboard interface on the Pi? Right now I do BIAB with a turkey fryer so I am just looking for something to monitor temps. Can you get more than 1 probe with just the PI or do you need the 1 wire adapter. I would really like to be able to use my android tablet or phone to see what the temps are. I also would like to expand in the future to using and electric element with a recirc pump and have the whole thing controlled by the Pi.

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Old 12-07-2012, 09:57 PM   #66
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redm18, the answer to your questions depend on the type of probe you get. If you get a Thermocouple or Thermistor then you can just use the onboard GPIO pins. The upside is that they are cheap and found just about everywhere; the downside here is that they don't have a linear curve so they require being calibrated around the temperature they will be used, which is just extra fanagling.

If you go with a digital probe, the most popular being the Dallas Semiconductor One-Wire DS18B20 although there are others, then you can also use the GPIO pins although it won't be as simple as reading a voltage. Often though there are libraries on the internet that do all the heavy lifting for you.

So with that out of the way I can answer your questions:

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Can you get more than 1 probe with just the PI or do you need the 1 wire adapter.
Yes. If you go with the analog probe routes, you can use up to 8 probes without any special extras. There are 8 General Purpose Input/Output (GPIO) pins that you could assign to watching those probes. If you go the One-Wire route, you can put something stupid like 1024 devises on one bus. The advantage of getting the One-Wire adapter is that you don't have to compile modules for the Raspberry Pi kernel to use the generic pins. You just plug it it and go. Although if you wanted to learn Linux...

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Right now I'm wondering if I would be better to get a 1 Wire adapter or just use the onboard interface on the Pi?
This is only a matter of choice. Both options work, it is just that the USB adapter costs $17 and will save some time as it is really just plug and play. If you want to use the pins on the Raspberry Pi you will need to add in the gpio kernel module (http://www.raspberrypi.org/phpBB3/viewtopic.php?t=6649). Although at the rate that the Raspberry Pi community is moving this may be in the more popular kernels by the time yours shows up.
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Old 12-08-2012, 02:54 AM   #67
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Seems like the usb is the way to go at least after reading the link thread. Any recommendations as far as which adapter to get?

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Old 12-11-2012, 03:26 AM   #68
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Quote:
Originally Posted by wdevauld View Post
helibrewer, don't get tangled up in AsyncIO/epoll just yet. It is very much a nice to have. Given that the rPi is probably going to be dedicated to the brewing/displaying there is little value in using epoll to free up the CPU for some additional cycles.

That said, I've done a few tours of building python web applications, so if you have your code in a public repo somewhere I can help you out.
Thanks! What I have so far is a PHP server side event script that uses system(cat ...) to pull the w1 GPIO data, I chop that up and turn it into a number where it gets called by a couple lines in the Gauge js and whalla, I have the gauges showing my GPIO temp data. It's kind of a kludge right now with no error checking/smoothing and even though I'm passing a float, the gauges are only showing integer data...I'll tackle that next. My goal is to get all 4 of my sensors working through the Gauge script then I will start clean-up and tweaking.
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Old 12-11-2012, 01:35 PM   #69
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Good work, guys.

I'll jump back into the fray once my stand is welded up, probably later this week. In the mean time, carry on !

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Old 12-11-2012, 10:49 PM   #70
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Stumbled on this while researching the Canvas Steel Gauges...
Pi for pulling sensor data

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Something is always fermenting....
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Brite Tank/Lagering:
Kegged: Hefeweizen, Chocolate Hazelnut Porter, Kumquat Saison, Tart Cherry Cider, Belgian Tripel, Maibock Bock, Ommegang Abbey Ale Clone, Belgian Golden Strong, German Pils (WLP830)
Bottled: Belgian Quad (Grand Reserve), Derangement (Belgian Dark Strong)
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