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Auxiliary outputs and protection against CO2 poisoning

After a while, I am back with news about the AquaSky development. I have been testing the unit on the aquarium for almost a year. It was necessary to adjust the values of some components. Anyway, it works fine.

The last thing I finished is the auxiliary outputs. Auxiliary outputs are used to control other devices that do not require PWM. For example the CO2 relay, fans or other supporting elements on the aquarium.

There are two outputs with the option of 5 V or voltage corresponding to the supply voltage of the unit. The on- and off-switching of these outputs can be programmed with the accuracy of one minute. It is also possible to add a trigger. A trigger means a condition for the output to be switched on and off. It is possible to choose the amount of current or power to switch on the output. Then a hysteresis is set. If the current (power) falls below the value reduced by the hysteresis, the output is switched off. The outputs are also over-current protected.

Why do we want to trigger CO2 by the amount of current or power? CO2 can be dangerous to fish if it is not consumed. And this can happen if the lighting stops working. In this case, the current will drop. So, if we measure the current, it is in our power to know when the light is off. And we can program the output to be turned off to protect the fish from CO2 poisoning.

In my case I use output 1 for fans and output 2, for the CO2 relay. The setting is:

  • Output 1:
    • Time window: 9.30 – 17.30
    • Trigger: none
  • Output 2:
    • Time window: 7.00 – 17.30
    • Trigger: Power, 10 W, hysteresis 2 W

So, the fans are turned on at 9.30 and turned off at 17.30. The CO2 is turned on as soon as the power exceeds 10 W, not earlier than 7.00. And it is turned off as soon as the power drops below 8 W, but at 17.30 at the latest.

I demonstrate this functionality in the following video. To facilitate the video recording I used different settings. There is also a simulation of the light fault which will turn off the output. As I mentioned, the outputs work with the accuracy of one minute. It means the output is not turned on or off immediately. The trigger does not take the instantaneous value of current or power. It takes the last minute’s average value.

I created a controllable outlet for the CO2 relay. The outlet is switched by 5 V. I’ll write about the outlet in another article.



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