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How do you have the thermistor wired? The Home Automation v4 has an on-board 15kOhm resistor (manual - page 12). Our Temperature Sensor Wiki has instructions for adding a 10kOhm resistor for the dedicated ADC's but those don't have a resistor on-board already. You could add a 30kOhm (check my math, I'm not an expert) resistor in parallel with the 15kOhm on-board resistor to effectively achieve a 10kOhm reading. See page 13 in the manual. (Images also pasted here since the manual locations may change over the years) |
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@Hect0rG You will recall I was working on getting the Home Automation V4 board supported in REM last fall, but unfortunately the cooler fall temperatures in Ontario, Canada and the need to close my pool for the winter ground my efforts to a halt. Given that the reopening of my pool is coming up on my agenda, I have been back poking around at the REM code. The REM code calculates temperature assuming that the voltage divider constant resistor is 10k. As you have pointed out, on this board the constant resistor is actually 15k. The question is, what difference does it make, and is it worth changing the code to accommodate? I did some calculations to figure out the impact that using 10k rather than 15k has on the temperature calculation given that our board has a 15k ohm constant resistor. I am only a tinkerer, not a mathematician, but I think the actual impact is negligible. In the range of temperatures we are working within (say, 60F to 100F) the difference between the temperatures calculated with 10k and 15k is approximately 25 degrees - in other words, as a result of the inaccuracy the temperature using a 10k thermistor on this board reads about 25 degrees hotter than it should. I say "about" as I am using generic values for the calculations so depending on your actual thermistor's values, the magnitude of the difference will be different, but the important point is that across the range of temperatures it is virtually constant (differing by about 1.5 degrees across the range from 60 to 100). The takeaway of all this is that you can adequately accommodate for the inaccuracy by doing what you have done - obtaining a reference temperature (using a regular thermometer), calculating the difference between that temperature and temperature reading in REM, and using the difference as the calibration offset. As a result, I don't think it is worth the effort to amend the code, though in a perfect world, you could. |
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@marthoc I did try that but the fluctuation in temperature was pretty off ( 22 degrees) which is why I opened this thread initially. Since your last post, I tried something new. I had a few 15k 5% resistors here so I put two in series to create a 30K resistor. This will allow me to get the equivalent of the 10K resistor that REM is expecting when put in parallel. To test, I put one end of the resistor on the 3V3 pin of the raspberry pi header and the other end on the A1 input to the sequent card. This basically mimics putting the resistor in parallel. The problem is I am still seeing fluctuations. For example last night I calibrated the ambient temp sensor with the new resistors in place and both it and another temperature sensor (Govee H5072) were reading aprox 68 degrees Fahrenheit. Here you can see how both temperatures differ although they come back together when it gets to about 68 degrees which was the temp when I calibrated them.
Now that I have the correct 10K resistor, I still think there is some issue with the calculations |
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@marthoc hate to admit it but the govee was in fact not reading correctly. My pool ambient probe is just under the while box for my chlorinator. I put all three of the thermometers I had in hand and notice the govee is off by 3 degrees. The govee meat thermometer on the left had both probes measuring 77. The Acurite on the right was locked on to the meat thermometer as was the pool controller. When I look at them while in front with the exception of the govee in the middle the temps seem to stay locked within .5 degrees which is acceptable to me. I do see some fluctuations during the day when looking through homeassistant but those I feel are due to the meat thermometer not having good connection via Bluetooth and only updating every 30 - 60 minutes. When inside it updates every minute or so. I ordered a mercury thermometer so I can do that final test soon. I'll report back but I think this was my issue. |
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This is what I see for the past 4 hours. I eliminated the original Govee Temp probe. These two are the meat thermometer probes and the pool ambient temp. Weird how they cross each other. I would expect them to be in sync. |
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I have had incorrect temp settings for a bit and decided to take a look. I believe I have it all set up correctly but I find the calibration values need to be adjusted much more than I am expecting.
I am using a Sequent Home Automation V4 board which I know is not one of the suggested boards but so far its been working well for my needs ( except fotr the temps).
Here is my setup.
Notice my calibration value of -17.2 ( this seems like too much of an offset to be correct)

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