- Joined
- Jun 21, 2012
- Messages
- 4,865
@Madsalts: Well, it seems you are quite serious about the care and feeding of saltwater aquariums. It is a keen observation that migration of the aeration bubbles across the top of the water to the opposite side is a reliable indication of too much DOC content. Who would of thunk it? You might even be able to patent and commercialize this concept (unless someone else has done so already!) if you can implement it.
From my point of view your problem has two main parts: (1) how to detect the arrival of a bubble (or bubbles) on the opposite side of the tank and (2) how to control an AC outlet that will, under time-programmed control, turn the protein skimmer on and off. Clearly you do NOT want the skimmer to operate continuously, or even on a programmed timer cycle, but only when the DOC concentration is higher than necessary for optimum aquarium health, as evidenced by the arrival of bubbles on the opposite side of the tank produced by the aeartor. I have to assume you are building a reef aquarium that supports fish and live coral formation, hence the requirement for some DOCs to "feed" the live coral rather than NO DOCs which a continuously operating skimmer would try to invoke.
Part (2) of the problem is almost trivial. Given a proper and reliable bubble sensor, a battery-operated Microchip PIC microcontroller could operate for months from three or four D-sized dry cells. The PIC would have a DC output that controlled a solid-state AC switch to operate an AC outlet the protein skimmer is plugged into. These solid-state switches have an optical isolator that provides galvanic isolation (usually to at least 1000 VAC) between the two DC control input terminals and the two AC load terminals. The control input is usually just a light-emitting diode optically coupled to a light-sensitive transistor, or sometimes to an optically-triggered AC thyristor. The more sophisticated versions have zero-crossing turn-on circuits that delay conduction of the load until the AC line voltage passes through zero, which can help reduce line-conducted radio-frequency interference (RFI) in some instances if that should turn out to be a problem. Probably not needed for your application. The major consumer of the control input power is the LED, typically a few volts at a few milliamperes of current, so we are talking milliwatts here. Still, the lower the better to extend battery life since the control input will be on as long as the skimmer is running.
Part (1) of the problem requires some more investigation by you. I doubt that a bubble detector based on electrical conductivity will be practical or reliable, especially in a saltwater environment. My suggestion is to try an optical approach based on submerged, upward pointing, infrared-emitting LEDs and matching, downward pointing, infrared photo-diodes mounted above the water. The exposed wiring should of course be well-sealed with clear RTV cement. A passing bubble should produce a large change in the photo-diode conduction. You may need more than one pair of emitter/detectors to ensure capturing a "bubble" event. A simple reverse-biased photo-diode feeding a trans-impedance connected op-amp should be sensitive enough. The op-amp output would be directly connected to an A/D input or an analog comparator input on the PIC to detect bubbles and respond according to its internal program. PICs come with one or more software programmable timers, as well as a "sleep" mode to conserve power until a bubble event wakes it up. Okay, so maybe the programming isn't trivial, but it isn't rocket science either and there are several of us here who can help you with that. The hardware is relatively simple and inexpensive.
Hop
From my point of view your problem has two main parts: (1) how to detect the arrival of a bubble (or bubbles) on the opposite side of the tank and (2) how to control an AC outlet that will, under time-programmed control, turn the protein skimmer on and off. Clearly you do NOT want the skimmer to operate continuously, or even on a programmed timer cycle, but only when the DOC concentration is higher than necessary for optimum aquarium health, as evidenced by the arrival of bubbles on the opposite side of the tank produced by the aeartor. I have to assume you are building a reef aquarium that supports fish and live coral formation, hence the requirement for some DOCs to "feed" the live coral rather than NO DOCs which a continuously operating skimmer would try to invoke.
Part (2) of the problem is almost trivial. Given a proper and reliable bubble sensor, a battery-operated Microchip PIC microcontroller could operate for months from three or four D-sized dry cells. The PIC would have a DC output that controlled a solid-state AC switch to operate an AC outlet the protein skimmer is plugged into. These solid-state switches have an optical isolator that provides galvanic isolation (usually to at least 1000 VAC) between the two DC control input terminals and the two AC load terminals. The control input is usually just a light-emitting diode optically coupled to a light-sensitive transistor, or sometimes to an optically-triggered AC thyristor. The more sophisticated versions have zero-crossing turn-on circuits that delay conduction of the load until the AC line voltage passes through zero, which can help reduce line-conducted radio-frequency interference (RFI) in some instances if that should turn out to be a problem. Probably not needed for your application. The major consumer of the control input power is the LED, typically a few volts at a few milliamperes of current, so we are talking milliwatts here. Still, the lower the better to extend battery life since the control input will be on as long as the skimmer is running.
Part (1) of the problem requires some more investigation by you. I doubt that a bubble detector based on electrical conductivity will be practical or reliable, especially in a saltwater environment. My suggestion is to try an optical approach based on submerged, upward pointing, infrared-emitting LEDs and matching, downward pointing, infrared photo-diodes mounted above the water. The exposed wiring should of course be well-sealed with clear RTV cement. A passing bubble should produce a large change in the photo-diode conduction. You may need more than one pair of emitter/detectors to ensure capturing a "bubble" event. A simple reverse-biased photo-diode feeding a trans-impedance connected op-amp should be sensitive enough. The op-amp output would be directly connected to an A/D input or an analog comparator input on the PIC to detect bubbles and respond according to its internal program. PICs come with one or more software programmable timers, as well as a "sleep" mode to conserve power until a bubble event wakes it up. Okay, so maybe the programming isn't trivial, but it isn't rocket science either and there are several of us here who can help you with that. The hardware is relatively simple and inexpensive.
Hop