Electronics - Aquaponics - Demand feeder PVC mockup

I think I have a final design idea for my demand feeder. It's only a mockup, at the moment, ie: it's only the PVC parts without any electronics or bearings.

The more I learn about this electronics stuff, the more places within aquaponics I can see uses for it.

I'll do a proper one of my Build posts when I have everything in order, but this is where it's at right now.

The basic design is a 90mm pvc section to hold the electronics (seen at the back or top left).

This keeps the electronics away from the feed and any moisture in a grow house or that just might be splashed around by fish expressing joy at their new feeder.

The electronics section is coupled to a 90mm T-junction to integrate the hopper.

In this case I've used a soft drink bottle, but any sized hopper could be attached. Another option would be one of those office water cooler bottles. Clear so you can see how much feed remains.

Perhaps for ease of refill, the top of a bottle could be cut of to act as a funnel. This could be screwed into the cap allowing the user to simply upend a similar bottle full of food into the hopper funnel.

Finally, the feed is delivered via an PICAXE controlled electric motor, rotating a screw in a 55mm (I think) PVC inner pipe. This holds the front bearing (the rear bearing is the motor, and is housed within the electronics section.

I cut an outlet hole to actually deliver the feed to the fish. I set the hole at the bottom rather than just letting the feed flow out of an open end to avoid water dripping into the feed. This could turn it into a gluggy mess, and jam the system.

The final mockup looks like this.

It'll work.
























Not just Electronics - Aquaponics - Demand feeder PVC mockup -  120 Things in 20 years

Aquaponics - Restricting the feed intake to a system

This post relates to my ongoing electronics project Electronics - PICAXE fish feeder

The feed able to be dropped into the system is limited by the population of bacteria. They are in turn limited in population size by the amount of available real estate on the grow media, and to some extent other surfaces and even free floating within the water.

It's the bacteria that process the fish exhalations and excretions. As fish poop and breath, they add to the ammonia load within the system. The bacteria convert the ammonia to first nitrites, then nitrates. It's the nitrates that most plants enjoy, and the nitrates are not toxic to fish until they are very high.

Ammonia and nitrites one the other hand are very toxic to fish.

So we need to be careful not to overstock our systems with fish, but more importantly, we need to not over feed our systems.

And it really is the system we are feeding, not just the fish.

Generally in aquaponics, we talk about maximum fish stocking levels within a system, but it might be just as useful to talk about maximum feeding levels for a given amount of grow media.

In a small system like mine, I long ago gave up on the idea of eating fish every week. My feeding regimen isn't really about maximising fish growth. I have a set maximum amount of feed that I can add to the system without seeing ammonia and nitrites. When I feed my fish I have a little jar with a level marked on it. I fill the jar to that level each day, and don't ever feed them more than that. I feed them less that that, if the don't want to eat it due to temperature, or whatever fishy reasons fish have for not eating, but they cant ever have more because because the system cant ever have more.

Actually the system can have a bit more, but this way when I find caterpillars and worms and things I can add them at will.

Generally speaking it's also a good idea to run your system below it's maximum feed capacity, so that if something goes wrong, you have some margin for error.

If, for instance, a fish were to die and I didn't notice it for a few days, it would create a huge ammonia spike. That ammonia might take a few days for the system to process, and in my system, I'd get away with it, but if I ran my system closer to it's maximum feed input, an event like a fish death could be catastrophic.

It's ok to run your system close to the edge, but you have to be there all the time, and check it all the time.

I prefer being relaxed.



Not just Aquaponics - Restricting the feed intake to a system - 120 things in 20 years

Aquaponics - String feed counter

The small volume of the food that's being dumped each time my on demand feeder triggers makes it difficult to measure, so I've been trying to figure a way to register trigger events.

My fist attempt at measuring the times when my fish triggered the feeder was a small spot of blutack on the top of the shaft. If the shaft moved while I was away, I could tell. But it turned out that the shaft turned one full revolution on at least one occasion, so there was no way of know if the fish had triggered it or not because the blutak was right back to where it started.

The next was a small pebble that I could leave sitting on the top of the shaft. If triggered, I would find the pebble lying next to the shaft. This worked but could only measure one trigger event before I would need to notice it, and reset it.

My latest design is a piece of string attached to the shaft, with a nut on the end for a weight. When the fish trigger the demand feeder, the string winds around the shaft, and raises the nut up.

It wont tell me exactly how many times it was triggered, but will give an indication of how long the motor ran in the time since I last reset it. Each time the fish hit it, it seems to turn approximately one revolution, so I should be able to mark off a rough guide on the wood. This should make a reasonable gauge to tell me how active the fish have been in setting off the feeder.

Aquaponics - Demand fish feeder success

I think I can safely say my fish feed themselves now.

Its been only five days since the fish first set eyes on my on demand feeder, and in the last 12 hours they have triggered it around eight or nine times.

They seem quite casual about using it now. Although The smallest of the fish in the tank just lurks near the lever, looking up at it. This little guy spends almost all his time looking at the lever, waiting for someone else to press it.



Water tests are showing no ill effects from the new feeding method, although I wouldn't expect them to. Feeding gradually all day rather than in large lumps a few times a day, should see the ammonia load maintain a nice steady level. A stable ammonia level, in my case zero ppm, should allow for the bacteria to maintain a relatively stable population. As far as I can see it should make the system a little more forgiving, and generally more stable.

Another advantage is that there should be less wasted food. With my regular method of hand feeding, I fed the fish until they stopped eating the feed. This meant that every time I fed them, a small amount would be left uneaten, to sit on the bottom. This represents no great loss because uneaten food all turns to plant food in the end anyway, but the plant food may as well go through a fish before being eaten by the plants.

My next step will probably be, to add a hopper to feed the auger. This will only need to be something like an empty soft drink bottle upside down over the PVC chute. While I'm at it, it would be a good idea to weather proof and possum proof the entire device.

All in all this experiment has turned out to be a complete success.

The cost for the motor and gearbox was around AU$20. I used a short length of flexible plastic tube to connect the gearbox shaft to the auger, which I already owned.

Aquaponics - On demand fish feeder

A while ago I tried to make a fish fed fish feeder design that would allow the fish to feed themselves.

I think It's made.

I say "think" because the fish have only triggered it twice in its first 12 hours of it being set up in their tank, and it's too early to tell if it works.

I bought a small 12 volt electric motor and gearbox, and connected it to an old drill bit from a hand cranked wood drill.

I cut a section of PVC pipe lengthways as a feed hopper, and filled it with feed.

The gearbox on the motor means the output shaft spins at only 36 revolutions per minute, and is quite powerful.

The next step was to find a switch that was very delicate to operate, so the fish could just lightly touch it to activate the motor.

I found a suitable lever switch, and glued on a plastic knife to extend the lever down into the water.






Now if the fish touch the lever, the motor engages, rotating the drill bit, forcing a small amount of feed along the PVC hopper into the fish tank.


I added a key, and a clip from my office as additional weight to set the trigger closer to being activated so the the fish need not hit the lever so hard.

It does actually seem to work, and the fish have set it off twice so far.

Only time will tell if it will really work as a feeder, or if every now and again, a fish just bumps into it and never associates the drop of food with the press of the lever.

[Note from the future - there is a LOT more to this project in later posts, including a new digital version where you can set the total amount of feed from a pinch to a bucket, and a stack of other features including a dawn reset so the fish can live on natural time rather than Greenwich imposed human time - there is also a video of the fish feeding themselves, and here is the results of a search on this blog for fish feeder for a stack more information]