Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > DIY Projects > DIY temp probes with DS18B20

Reply
 
LinkBack Thread Tools
Old 01-02-2011, 09:51 PM   #1
bolts
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2009
Location: Portland, OR
Posts: 306
Liked 8 Times on 7 Posts
Likes Given: 3

Default DIY temp probes with DS18B20

I've read some very helpful threads already -- summing up my plan w/ some questions. I could just buy these from Derrin -- but that's hardly any fun

http://www.homebrewtalk.com/f51/make-your-own-precision-ss-temperature-probe-101192/

http://theelectricbrewery.com/temperature-probes


Parts

- 4" stainless probe ends (from Brewers Hardware)
- M8 Male cable w/ leads (for the sensor end)
- M8 Female/Female cable (sensors to project box)
- M8 Male connector (for project box)
- DS18B20 (temp sensor)
- thermal paste
- heat shrink (adhesive & normal)


The Plan:

- solder the DS18B20 to the M8 Male w/ leads (may shorten the leads to ~4" outside the probe)
- cover all exposed connectors/solder joints with heat shrink
- add thermal paste to bottom of thermal probe
- insert probe/cable assembly and seal the top with adhesive heat shrink

It all seems pretty simple really (famous last words...)


Questions:

- I plan to run these in non-parasitic mode as it has been more reliable with my futzing around so far. Does it matter in practice other than needing to do a strong pull-up when doing the temp conversion?
- Do I need a cap in the probe end for anything? I've seen mentions of small caps across Vdd and GRD.
- Is there value in 4-wire cables? Are they actually twisted pair inside? If I read write, I should run DQ/GRD on one pair and Vdd on the other pair.
- Is the thermal paste going to potentially create problems shorting out sensors?
- Any cheap sources for M8 cables/connectors?

__________________
bolts is offline
 
Reply With Quote Quick reply to this message
Old 01-19-2012, 04:40 PM   #2
mxc1090
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2011
Location: idk, PA
Posts: 10
Default

4" seems a bit long. The response time of the sensor will be greatly reduced. (I've tried, took almost a minute to register a change)

Heatshrink the three leads individually, but do not heatshrink the plastic.

Thermal paste usually has a high thermal conductivity, but a low to non-existent electrical conductivity. No need to worry about a short from that.

The caps would help on sensor like the LM34/35, but this is digital and not necessary for the length you are using (assuming less than 20-50ft).

Good choice on the DS18B20, I had 5 running on 1 wire and all within +-0.5*C. I would recommend not using parasitic power, just because of longevity and the fact that it is not necessary in this case.

In my probes I use a 4-conductor phone cable and use some old phone jacks so I have a modular design. I also use 1.5-2" stainless tubes, thermal paste inside, stress relief with silicone inside then the outer opening with 'WaterWeld" by JB Weld. (food safe, 300*F). Response is probably around a few seconds, never checked it.

Of course this is all linked up to an Arduino...

__________________
mxc1090 is offline
 
Reply With Quote Quick reply to this message
Old 01-19-2012, 06:31 PM   #3
audger
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2011
Location: ., Connecticut
Posts: 1,497
Liked 40 Times on 40 Posts
Likes Given: 1

Default

Quote:
4" seems a bit long. The response time of the sensor will be greatly reduced.
i dont agree. i use several probes made almost exactly as the OP plans, and they begin to register a change nearly immediately. they are 2, 6 and 8" long. obviously, the more material to heat or cool, the longer it will take to do so. normally it takes less than 10 seconds to register a 10-20 degree change in my experience. the amount of material directly around the sensor is what matters most, and tha tis the same regardless. it doesnt matter much if there is 2 or 20 inches of tubing behind it.

Quote:
Thermal paste usually has a high thermal conductivity, but a low to non-existent electrical conductivity.
that greatly depends on what exact thermal paste used. i didnt use thermal paste, as i only had arctic silver 5 on hand, and that is conductive. i ended up mixing 90-95% powdered aluminum, 5-10% silicone caulk, by weight. works just fine. as long as the paste is specifically non-conductive, its fine to use.

no capacitors are necessary. only a 4.7k pullup resistor on the data line. capacitors would prevent the controller from pulling the line low, and would prevent the reset() commands from working.

i agree that if you can easily avoid parasite power, do that. using only two wires /should/ be fine, but if using a 3rd wire isnt a problem at all, just do it.
__________________
audger is offline
 
Reply With Quote Quick reply to this message
Old 01-19-2012, 07:14 PM   #4
mxc1090
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2011
Location: idk, PA
Posts: 10
Default

Quote:
Originally Posted by audger View Post
i dont agree. i use several probes made almost exactly as the OP plans, and they begin to register a change nearly immediately. they are 2, 6 and 8" long.
I may have over exaggerated the probe length, but I would still recommend the smallest size to comfortably fit everything inside.

Quote:
Originally Posted by audger View Post
that greatly depends on what exact thermal paste used. i didnt use thermal paste, as i only had arctic silver 5 on hand, and that is conductive. i ended up mixing 90-95% powdered aluminum, 5-10% silicone caulk, by weight. works just fine. as long as the paste is specifically non-conductive, its fine to use.
Arctic Silver 5 is a thermal paste (compound) and is most certainly not electrically conductive. I use it on CPUs + GPUs all the time.
Arctic Silver Incorporated - Céramique 2

___

I would recommend keeping the 4K7 resistor outside of the probe to avoid space constraints and possible heat addition.
__________________
mxc1090 is offline
 
Reply With Quote Quick reply to this message
Old 01-20-2012, 12:11 AM   #5
cobolstinks
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2008
Location: Rochester, MN
Posts: 229
Liked 2 Times on 2 Posts

Default

you dont need thermal paste if you go with the brewershardware probe ends. The sensors fit snuggly into the probes without much room between the sensors and the probe wall, i just built four of these senors in a netduino project last week. I used 3 10" probes and 1 4" probe.

I would go with longer probes because you want to have your sensor in the middle of your pots. With the 1/4" compression fittings also sold at brewershardware you can adjust the probe depth as long as you used the o rings and not the permanent metal compression pieces. Just my $.02.

__________________
cobolstinks is offline
arkham_razors Likes This 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Love temp probes Ed_ DIY Projects 7 06-03-2010 08:07 PM
Temperature probes, what are you using? babalu87 DIY Projects 5 02-01-2010 01:51 PM
Panel mount connectors for RTD temp probes - how about these? kal DIY Projects 13 04-02-2009 12:47 AM
Sanguino / DS18B20 wiring HomebrewJeff DIY Projects 2 02-10-2009 01:11 AM
digital probes for temp controls on herms/rims nathan DIY Projects 1 12-13-2008 02:10 PM