Dew Heater Not Turning Off

[ldb20151]

After the earlier discussion on the dew heater thresholds, I reset the lower delta threshold to 40 to see if the dew heater would tun on as I believed it should. Fortunately, it did turn on. I then changed the low delta threshold back to 15 degrees and expected the heater state to return to off. I noticed the DEVICES/DEW HEATER setting reported the heater transitioned to off (0), but the latest image and the dew heater chart both show the heater remains on. See pictures below. I've waited quite a while for the change to propagate, but no good so far. As shown in the picture below, its been 20-min since the change back to low threshold delta of 15 but the heater remains on. What am I doing wrong? Just when I though I understood how these setting work, I hit a snag.
v/r,
-Larry

[aaronwmorris]

What do the logs say about the status?

grep "Dew Heater threshold current" /var/log/indi-allsky/indi-allsky.log | tail -n 200

[ldb20151]

Context -- after being unable to get the dew heater to turn off by reseting the delta threshold to 15 (vs 40), I phyiscally checked the heater and confirmed it was on/heating. So, I rebooted the system. When it came up, the dew heaters were off as they should have been. When I saw your note, I first set the low delta threshold back to 40 and waited for the heater to turn back on -- which it did.

I'm a linux newbie -- when I execute the suggested command, I get a file not found. Not sure why I have a different file structure as I used the wiki installation process. With my limited knowledge I modified the command as follows; results are shown.

:~ $ grep -r "Dew Heater threshold current" ~/indi-allsky | tail -n 200
grep: /home/larry/indi-allsky/indi_allsky/pycache/sensor.cpython-311.pyc: binary file matches
/home/larry/indi-allsky/indi_allsky/sensor.py: logger.info('Dew Heater threshold current: %0.1f, target: %0.1f, delta: %0.1f (%0.0f%%)', current_temp, target_val, dh_temp_delta, self.dew_heater.state)

Does this provide the data needed? It appears to me, the info is being logged someplace but I don't know where to look. I'm attaching my support info hoping that will be useful. Sorry I'm not more knowledgeable.
-Larry
ldb20151 Support Info.pdf

[aaronwmorris]

I had a typo in the path. I corrected it above.

[illigtr]

I am experiencing similar issues...

I built a dew heater using 32 ohms of 10W resistors connected to a MOSFET driven by 12 VDC. The gate is controlled by an opto-isolator.
Since the MOSFET is deactivated by gate to ground via the opto-isolator, I am using OUPUT - Inversed.

The pins I have tried on my RPi-4B are GPIO19 (hardware PWM) and GPIO26 (software PWM). REGARDLESS of my setting for output inversion, I always read 0V on the GPIO pins.. which means my heater is running 100% of the time.

Logs show this in all cases:

2025-09-18T14:45:48.827483-04:00 indi-allsky [INFO] Sensor-1-1142/MainThread sensor.check_dew_heater_thresholds() [608]: Dew Heater threshold current: 27.1, target: 15.7, delta: 11.3 (0%)
2025-09-18T14:46:14.185253-04:00 indi-allsky [INFO] Sensor-2-1252/MainThread sensor.check_dew_heater_thresholds() [608]: Dew Heater threshold current: 27.1, target: 15.7, delta: 11.4 (0%)
2025-09-18T14:46:29.482237-04:00 indi-allsky [INFO] Sensor-2-1252/MainThread sensor.check_dew_heater_thresholds() [608]: Dew Heater threshold current: 27.1, target: 15.7, delta: 11.4 (0%)
2025-09-18T14:46:44.761165-04:00 indi-allsky [INFO] Sensor-2-1252/MainThread sensor.check_dew_heater_thresholds() [608]: Dew Heater threshold current: 27.1, target: 15.7, delta: 11.4 (0%)
2025-09-18T14:47:00.044499-04:00 indi-allsky [INFO] Sensor-2-1252/MainThread sensor.check_dew_heater_thresholds() [608]: Dew Heater threshold current: 27.1, target: 15.7, delta: 11.4 (0%)

Here is my current config.

What could I be missing here? I have daytime enabled simply to be able to test.

[illigtr]

Ok. I have figured this out. The "Invert Output" is not being handled correctly.

To get my dew heater to work with inverted output I had to temporarily DISABLE "Invert Output" and enter all the PWM values as a complement of 100%. Now it works... When I expect my dew heater off, I can now read 3.3V on GPIO 19.

[illigtr]

I opened an issue and found the bug and have advised the author. 2387.
You can make a quick fix by reviewing my answer in the issue, if you are inclined to edit python code (only 1 line needs to be edited). I am pretty sure the author will fix this soon, in any case.

[aaronwmorris]

Merged #2392 . I caused this bug by trying to fix another bug in #2207.