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CM2302 got done in — Parallax Forums

CM2302 got done in

Early in the summer I had placed a cm2302 temp/humid sensor outside to data log the readings. Well last night the -13.50 degrees temperature put my cm2302 into a frozen state. So, far the readings keep showing -13.50 while the temperature outside is actually +3 degrees. Now I am wondering if the sensor is fried, no, I mean frozen, and no longer functional. I am hoping it is just in hibernation until the temps get well above 32 degrees.



  • says here that the sensor should be good to -40C...
  • Sometimes there is moisture in the air that can become trapped on the sensor causing it to freeze up and give false readings.

    You need to thaw it out.

  • Since you mentioned "above 32 degrees," you must be measuring in Fahrenheit. The -40°C limit is -4.44°F, so your outside temp has gone well below the sensor's lower rating.

  • I just went outside and took a quick look at the unit, it does not look like it imploded or exploded, so, maybe if I am lucky, this Saturday when the temps are expected to get close to 40*F, the unit will thaw out, I hope. Otherwise, I will be waiting for some nice spring weather, in April, or so, to give it a replacement, if it is what is needed.

    I guess I will have to start looking for a unit that can work in -20*F and at the top end, about 105*F.

  • -40c = -40 degrees Fahrenheit.

    I have the BME280 unit outside and it worked all the way down to -21 degrees this morning. No problem.

    I did however have this same unit last year set out in the open and it failed at 20 degrees. I ended up replacing it only to find out that once I had it in the house a while it worked just fine.

    I now have an enclosure around the unit and don't have a problem with it freezing up.


  • iseries wrote:
    -40c = -40 degrees Fahrenheit.

    Right you are! I applied 5/9 instead of 9/5. D'oh!

  • Since the cm2302 is rated for -40*F, interesting that -40*C=-40*F, I am hoping that it is just a problem with some excessive humidity that accumulated on the unit. Since I am data logging I will be able to check the data to see at what point/condition the cm2302 starts to work again, if in fact it does start to work again.

  • WBA ConsultingWBA Consulting Posts: 2,930
    edited 2019-02-01 07:55
    Ray, If you need to replace the unit and would be interested in switching to a Sensirion SHT15, let me know with a PM or here. I have nearly 200 sensors in stock right now and plan to build up some of my WBA-TH5M modules. The way my module is designed, you can use it with CAT5 for lengths of at least 208 ft. They are rated for -40C to +125C.
  • This morning I decided to reboot my Activity Board, and to my surprise the cm2302 is providing temperature data. Not sure about the humidity part, it shows 99.90 percent, while the local weather report shows 92.00 percent. Not sure if the Activity Board had a programming glitch or it was just the cm2302. I hope I do not have to start rebooting my Activity Board once a week, just to keep the running program fresh.

  • My configuration ran for several months before had to make some changes.

    I did add some logic that tracks time and also a dead man switch.

    So if the unit sends updates the timer will get reset. So far the unit has been running 26 days.

    See for yourself: My weather station


  • It seems I have some more problems with the Activity Board setup, my Parallax WiFi module had a glitch, I cannot bring up the WEB page for the unit. This has happened before, but I never could figure out what caused the problem. It seems like the setup runs flawlessly for a couple of months, and than it does not.

  • Yes, I think you maybe on to something there.

    I built an indoor unit that makes a web request to a site that gives me the forecast in my area. It works great for a while and then stops working. It make a web request every 10 minutes.

    I recently replace it with my own ESP8266 unit running custom code and that works just fine.

  • After unplugging the Activity Board and pulling the Parallax WiFi module a couple of times, I finally got a WEB page back up. Now I am starting to wonder about the Parallax WiFi module, it seems like it is starting to act up more and more. This Activity Board Parallax WiFi module setup has been on line 24 hours a day for about a year now, I think, maybe longer. Not sure what part is starting to fail, the Activity Board or the WiFi module, or maybe both. As for the cm2302, it seems like it is starting to show the temperature data consistently, but the humidity reading is still stuck at 99.90 degrees. Maybe later in the day when the outside temp gets over 32*F, the cm2302 humidity portion will fix itself.

  • You may have to bring it in the house for a while and warm it up to remove any excess humidity that maybe stuck in the unit.

  • That is a problem, it is not setup for a quick removal. Oh, well, some redesign of the setup this spring when the temperature out side is more bearable. I will probably have to relocate the unit because it is picking up extra heat from somewhere when the sun is in the area. The unit is not exposed so the sun shines on it, but it is picking up some built up heat source. Maybe if there is some direct sun, it looks cloudy outside right now, maybe the extra heat source will dry it out faster.

  • I just found out that the Parallax WiFi module is out of action, again. On previous occasions, when it stopped working as expected, I just unplugged the module and it seemed to start working again. This time, I get the feeling that the unit has given up. Even if it starts back up again, I have lost confidence that the unit will function properly.

    At this point I am not sure if the Activity Board has also been compromised in some way. This has turned out to be a real hassle, not sure what I will have to do too fix the problem. It is not like this unit is in some harsh conditions, it just runs 24/7 for months on end.

    Yes, as of yesterday, the cm2302, is showing the temperature correctly, but the humidity readings are still at 99.90 degrees. So, that is another puzzle that has to be solved.

    If a majority of the products that make up the Activity Board, Parallax WiFi, and the cm2302 are made in China, then I am becoming very cautious about buying anything that is electronic that has its origins in China. Hmm, what to do?

  • For my weather station I used a XBee WiFi module since the ESP product was not available.

    The way it is configured is that I first programmed the XBee to sleep for 1 minute and then wake up for 10 seconds.
    In my program then I monitor the CTS pin and when it goes high I gather the weather data and send it as serial UDP data out to my network. Then the XBee goes back to sleep.

    There is no fancy setup code for the XBee in my program and the XBee is set to transparent mode so all I do is send the data at 9600 baud to the serial port of the XBee. The XBee builds the packet and sends it.

    The thinking was that I could save power and run it from batteries but the propeller uses to much power.

    Since this module fits in the same place as the ESP module it would be a plugin replacement.

    Parallax used to sell that item but not anymore.

  • I am still thinking about how I could improve the situation. One thought that I had is setting up the web page using the Dell server. I am now streaming the data to the server using a comm port, I guess I could set up some python program to handle the incoming data and serve it up to the web page. It is so much more convenient to use the Parallax WiFi for doing that. Not sure which way I will be implementing at this moment.

  • About the CM2302 RH sensor, a friend pointed me to this advanced amateur metrology web site that has a careful analysis of that sensor as a function of RH and temperature.

    Also includes
    Bosch Sensortec BME280
    Measurement Specialties HTU21D
    Silicon Labs Si7021
    Sensirion SHT71, SHT31
    Aosong DHT11, DHT22, AM2302, AM2320, AM2321

    They didn't have means to test below freezing though. I believe that the AM2302 and the CM2302 are equivalent--not sure though.

  • Just an update. About a month ago, when the weather became somewhat warmer, I replaced the bad CM2302. When I got it inside, even after sitting around for a week or so, the module never came back to life, at least the humidity detection part of it.

    Now the new unit has gone bad also. The temperature reading is stuck at 65.10 *F. This module only took a month to get done in, not sure what the heck is going on with these modules. Did I get the only bad ones from a large production run. Boy, what luck I must be having with these units. I have a module that I am using inside the house, no problem with that unit. I guess I will have to take that one outside, just to see if that one goes bad also. Then I guess I could say that the CM2302 modules are not recommended for outdoor use.

  • Are the indoor and outdoor units using the same host system?
  • For the CM2302
    any code available for P1 I can only find code for P2

  • No, Blockly is easy to find - I want spin for P1. I found spin for P2 - guess that will not work on P1

  • @6aerobat said:
    No, Blockly is easy to find - I want spin for P1. I found spin for P2 - guess that will not work on P1

    Here is a spin file I found a while ago for the CM2302. It contains a P1 PASM driver implementation for the CM2302. I don't know if this will help you or not, but it is for the P1. As for the P2 spin you found, it may be possible to still use it on the P1, it will depend on the commands/methodology used.

  • msrobotsmsrobots Posts: 3,560

    well, with flexspin you can compile P2 Spin for the P1 as long as there is no pasm involved


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