I added a dew heater and temperature control for my AllSky camera

[chvvkumar]

I ran my camera without dew control for a few years. But I got tired of dew and decided to build one with dew control. It took some research as this was the first time I played with relays and buck converters but it is all working now. I thought it would be a good idea to document what I did in case someone else is looking to do the same.

Parts

MAKERELE Waterproof Electronic DIY Projects Cable Enclosure Outdoor 6.89”6.89”3.94”
https://www.amazon.com/dp/B08PB4N3SK

OwlCat 4 Inch Indoor Outdoor CCTV Replacement Acrylic Clear Dome
https://www.amazon.com/dp/B09GLPCG56

Dew Heater Module - All Sky Camera
https://www.dewcontrol.com/product/dew-heater-module---all-sky-camera

SD20 2pin Right Angle Waterproof Connector
https://www.amazon.com/dp/B07BL1DPSP

DC 12V/24V to 5V USB C Step Down Converter Type-C Interface 5A 25W
https://www.amazon.com/dp/B0CRVVWL4Y

SunFounder Relay Module Compatible with Arduino and Raspberry Pi 5V DC Trigger by HIGHLO (HIGH Trigger)
https://www.amazon.com/dp/B0151F3A9Q

Waveshare BME280
https://www.amazon.com/dp/B088HJHJXG

Arducam for Raspberry Pi Zero Camera Cable Set, 1.5" 2.87" 5.9" Ribbon Flex Extension Cables for Pi Zero&W, Pack of 3
https://www.amazon.com/dp/B085RW9K13

WAGO 221 Lever Nuts
https://www.amazon.com/dp/B0CJ5QF3VX

Ferrule Crimping Tool Kit (For the relay load cables)
https://www.amazon.com/Self-adjustable-AWG-23-7-Electrical-Connectors/dp/B0B23V7ZQJ

Circuit

Pictures

[Alex-developer]

Looks good :-)

[chvvkumar]

Apparently, a Pi5 and SSD generate enough heat in a sealed box that the dew point has never raised above ambient temp in the box and heater has not turned on yet.

[EricClaeys]

@chvvkumar, please keep us up-to-date regarding how the Pi 5 does in a sealed box. You are the first person I've heard of that's done that. I think of lot of people, myself included, are concerned about it being too hot.

[chvvkumar]

Will do. This weekend is supposed to be 57F (!) so it will give a good indication on how the Pi does. Otherwise summer is going to be a torture test here with 100+ degree temperatures here.

[chvvkumar]

I added a couple of pressure equalizing valves to the box. I figured with the heater and the Pi5, the larger temperature differentials inside and outside the box would cause seal integrity problems with the box.

Another reason was, sealing off the box makes the BME280 pretty useless as it won't be able to measure correct humidity and temperature levels outside the box.

The vents I use, they are waterproof but allow air to pass through the membrane:
https://mou.sr/49NGgYM

The before and after of adding these vents. While the humidity was ~9% with a desiccant before, the humidity in the box after adding the vent while higher, is still not the same as outside humidity as measured by my weather station (which was reading ~90%).

[EricClaeys]

Nice idea with the pressure valves. If they let humidity through, won't the inside humidity eventually be the same as the outside humidity, once the desiccant is saturated?
Does anyone make something like a half-full balloon that grows and shrinks based on pressure so lets the air expand and shrink without having any opening to the outside?

Do you plan to paint the top of your enclosure white to help keep the temperature down?

[chvvkumar]

I actually had that question when looking at PCVs. I could not get a good answer on whether these membranes allow humidity to pass both directions, even after reaching out to the manufacturer.

Here is the comparison between what my weather station reports and what the BME280 is reporting. Yellow is the weather station, blue is the akksjy:

I am speculating this is because, when the temperatures are equalized, there is minimal movement of air in and out of the enclosure. Air is only passed through when the temperature differential is large enough to cause a pressure differential. As such, night to day and day to night transitions and when the dew heater is ON is when there is opportunity for humidity to permeate into the box.

As for the black top, it was in fact Gray when new like the rest of the box, I plastidipped it black to minimize reflections off the dome.

For the ballon valves,these valves are IP67 rated at minimum. I am not sure about the balloon type valves but I did come across this interesting video that uses a balloon to demonstrate the effect of having a valve in place using a balloon during my research:

https://www.youtube.com/watch?v=4zFbJXowgYQ

[chvvkumar]

A little update on this. I have found that even with the pressure valve, the internal humidity is not changing that much; a couple of % points at most over seven days.

So the BME280 is pretty much useless to control the dew heater as it would only control for internal dew in the box. So I instead I am using my Home Assistant to figure out the dew point based on my weather station data and control the heater instead. I wrote a python script to grab this from MQTT and turn on and off the heater GPIO pin.

https://github.com/chvvkumar/RPi5_MQTT_GPIO_control

and made this module (still in the DEV branch of allsky-modules) to make this data available to the overlay:
https://github.com/AllskyTeam/allsky-modules/tree/dev/allsky_mqttsubscribe

What it looks like:

[Alex-developer]

and made this module (still in the DEV branch of allsky-modules) to make this data available to the overlay: https://github.com/AllskyTeam/allsky-modules/tree/dev/allsky_mqttsubscribe

I have merged the module into master :-)

[chvvkumar]

I just noticed it today, thank you! I had to reinstall allsky due to some issues I was trying to troubleshoot, adn noticed the module showed up when I ran the install script! While doing that, I also added a Shelly Plus 1 smart relay to the enclosure as an out-of-band power management thing for the camera. It runs off of the 12V power and switches the positive rail of the buck converter's input power. Now I don't have to unplug and replug the power every time I need to power cycle the Pi.

[ova103]

Hello @chvvkumar , can I ask you what the conditions (logic) are to turn the dewheather on or off? Thanks.

[chvvkumar]

I am using home assistant to control the heater, the logic is explained here:
https://github.com/chvvkumar/RPi5_MQTT_GPIO_control?tab=readme-ov-file#example-home-assistant-automation

TLDR: All these conditions need to evaluate to true for the heater to turn ON

1. Dew point + 10 degrees should be greater than ambient temperature (i.e. ambient temp is within 10 degrees of the dew point)
2. The heater is not currently running (determined by checking the status of the 15 minute timer)
3. Heater was turned on at least 60 minutes ago (determined by the 60 minute timer).

This runs the heater for 15 minutes every hour unless the dew point gets 10 degrees below the ambient temperature.

[ova103]

Thanks