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simple easy freezer monitor

 
Ebo David
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Well, hurricane season will soon be upon us and I thought I would share a trivial simple way to monitor your freezer, or other things of interest, during times of power outages and more -- by using an indoor/outdoor temperature monitoring station sensor in a zip-lock placed in the freezer.

The back story here is that my wife has an old large upright freezer in the garage.  Since it is old it has a few, ahem, issues.  One of which is that the door is slightly racked, you have to push both the top and the bottom of the door to get it to shut and seal correctly.  Unfortunately, from time to time we have guests that get in it and either do not know or forget, and we can loose the entire freezer worth of food before noticing.  Add to that, both she and I have food allergy issues, so loosing a freezer load of allergy free food stuffs can be *expensive*.  Also note that every time you open up an upright freezer you can loose a LOT of the cold, so you really only want to open it up a little as possible during an outage, but you also want to put it on the generator before it thaws out.  About a decade or so ago my wife asked me to check into building/installing a temp monitor for the outside freezer, and in a moment of inspiration I decided to make a little test -- take the outside temp monitor, put it in a zip-lock, and shut it in the freezer.   It has worked like a champ for 10 or 12 years:

When I got ready to post this I also decided to dig around and see if anyone has figured out a way to read them from your personal computer.  Luck would have it msells posted the following Monitoring of 3rd party temperature sensors with a computer (Linux, Thermopro, Raspberry Pi, DIY with no soldering!):

l;dr: (too long, didn’t read): The $43 ThermoPro TP-08S kit reports temperatures over 433.9Mhz and you can get a $20 Software Defined Radio (SDR) USB dongle to read them from a computer (Linux, RaspberryPi, possibly Android w/ OTG cable, Windows, +??). This seems like a nice gateway into remote monitoring. I’ve never trusted the Bluetooth stuff and while my Fireboard is cool, if I had known about this before I may not have bought the Fireboard (but their probes are so nice…).

Getting the USB dongle if you already have supported temperature sensors is inexpensive. The USB SDR I’m using is a “Nooelec NESDR Mini USB RTL-SDR & ADS-B Receiver Set, RTL2832U & R820T Tuner”. List of sensors is at https://github.com/merbanan/rtl_433 under the running section. It will probably also pickup your existing weather sensors and other "stuff" and let you log that from a computer. Windows info @ https://github.com/winterrace/rtl_433_win/releases Linux info at https://github.com/merbanan/rtl_433

#end-tl-dr

#Long geeky part starts here….

I wanted to build my own temperature monitoring system with multiple remote sensors and bought several micro controllers (ESP32, Arduino, ..) along with raw temperature sensors like the various DS18B20 options. Raw sensors are $1, waterproof ones are $2. I built some ESP32 hardware, things looked “nice”. But really I wanted to have remote sensors that I didn’t have to plug into USB or AC power so I was facing having to put batteries with each sensor and charge them. Solar? Wait, they’re not even weatherproof! I am not actually a hardware guy so this seemed like a lot of effort and parts.....

I took a pretty big 180 turn when I realized that a lot of the weather station kits (AcuRite 02082M with 3 sensors and a nice console for $76) would report in via 433.9Mhz and I could just get a $20 SDR USB dongle and listen for their incoming beacons with temperature information. $100 later it all worked as planned. I put one AcuRite sensor in my garage, another on my back porch and one in my refrigerator. All reporting into a Raspberry Pi (Linux) box.

So the next interesting thing that happened was I looked at the raw logs that https://github.com/merbanan/rtl_433 had produced and noticed sensors that were not mine! Amusingly some were TPMS, which seemed to correspond to Amazon delivery times - I know one delivery van has a low tire.  I got readings for home security stuff from probably a neighbor about glass break sensors. A few days ago while reviewing the logs I noticed something more interesting for BBQ folks:

{"time" : "2019-12-04 04:17:14", "model" : "Thermopro TP11 Thermometer", "id" : 0, "temperature_F" : -4.000}

Wait, that’s not my Thermopen, is it?! Oh, no my Thermopen broke a second time and I haven’t sent it back in for repair because I’m annoyed it broke AGAIN. Uhh, read more carefully.. Pen != pro And it’s reporting really cold! Not me… But this suggested that ThermoPro thermometers talks on 433Mhz as well! So I fired up my ThermoPro TP-08S ($43 on Amazon) in my office. It’s a pretty commonly recommended RF “one on the grill, one in the meat” starter kit. I have that and a full on FireBoard too.

Boom!

{"time" : "2019-12-05 19:55:41", "model" : "Thermopro TP12 Thermometer", "id" : 28, "temperature_1_F" : 71.780, "temperature_2_F" : 71.240}


#end geeky part

I haven’t followed the HeaterMeater situation after I got my FireBoard but for anyone wanting monitoring only that doesn’t want to solder anything and already has a compatible sensor this is probably nice info & not much money. Compatible devices are listed on (https://github.com/merbanan/rtl_433).

I'll probably try it out on my next cook (I don't cook often) - more probes makes things taste better, right? Without a fan control this isn't what I'm going to pursue but I'll probably toss my USB SDR in a bag if I'm taking the ThermoPro for travel.



I plan to give this a try as well.  The nice thing about these sensors is that they are easy to find and are probably 100x cheaper than loosing a 15 to 20 cubic feet of frozen food.
 
James Whitelaw
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We got this Temp Stick Wireless Remote Temperature & Humidity Sensor for monitoring an empty structure and while not the cheapest option it has been very reliable and can be customized to give alerts when the temp or humidity gets out of a set parameters.
 
Ebo David
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Thanks.  I am planning to play with the ThermoPro TX-5 and see how it does.  The nice thing is that the outside unit was designed to take a driving rain, but still cannot be submerged in water.  I forget the IP rating, but it is likely something like a IP65.  
 
Anne Miller
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Ebo, thank you for sharing.  I didn't know things like that existed.

I have a small refrigerator, like the dorm room kind, that I turn into a freezer.  I just keep an indoor/outdoor thermometer in it.

For our other freezers we use this:



Amazon Link

 
thomas rubino
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Hi Ebo;    I am using a weather station to monitor our outside freezer.
Works great!  I did not put the sensor in a baggie though. Can you tell me why that is a good idea?
Its been several months now with no transmission issues.
I did buy and try a specialized for freezer remote monitor. Don't waste your money!  It failed miserably. Would not transmit from our barn to the house. Worked for about 10' until you stepped out the door.
The weather station on the other hand is performing 100% of the time.
My old weather station automatically rotated between sensors.  The new one stays on one sensor and must be switch to read the others.... not a big deal.
Current freezer temp. mid way up the freezer is 9.3 F.  with 81% humidity!   Perfect!  
Current out door temp. 39.0 F 88% humidity
Current greenhouse temp. 46.3 F with 58% humidity
 
Ebo David
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@thomas, I put it in a baggy because the humidity is condensing(?) into ice.  I did not want ice crystals to form in the humidity sensor itself.  Besides I did not see a need to monitor the humidity inside the fridge.  Would it be meaningful?  Anyway, I probably can remove it from the bag, but it has worked for  to 10 years that way without loosing a sensor (just have to replace the batteries when the monitor goes blank).
 
thomas rubino
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If it works Ebo  do not change a thing.
I never gave a thought about losing a sensor to ice. Its certainly possible.
Maybe I'll toss mine in a bag and see if the humidity changes.  
I agree, I know of no real reason to monitor humidity in a deep freeze.
 
Ebo David
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@thomas, when I first read the reply I went and looked it up.  Turns out that lack of humidity causes freezer burn, so it apparently makes a difference.  That said, our freezer does not have any way to increase the humidity, and I am not sure with the problems we have with icing that I would want to add more 8-0
 
Ebo David
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Very likely the last post here.  The new Thermapro 3-channel temp/humidity monitor + 3x sensors are running in the two freezers and outside.  I also figured out how to configure the NooElec SDR to read them using rtl_433.  Works are expected.

Sweet!  Also sweet!!! is the fact that I can purchase Thermapro external sensors to replace the rest as they go out and they do a good job of being backward compatible...

So, here is keeping it cool!
 
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