Aquaponics - Electronics - Digital demand fish feeder

The water temperature in my aquaponics fish tank is today sitting at around 20c This means my silver perch are back to feeding like crazy.

I suspect they would eat a lot more if I fed them 20 times a day, so I rummaged around in the darkest depths of my house, and found my demand fish feeder project.

When I made it as part of trying to learn electronics, I happened to be on lots and lots of morphine because I had a rock festering in my kidney. At least I think that's what it was for.

Geology is interesting and all, but who wants to grow rocks in your kidney.

Anyway, it seems that whatever you learn when your brain is in an opiate fog stays in that fog. At least it did for me.

Every now and again I've discovered this poor little open source project, and tried to figure out what it does, and why it doesn't do what it should do, and it always ends in my just putting it back into the darkest part of my house, and leaving it there until for some new reason I think I'll understand it again.

Yesterday I looked at it and it made sense.

Only a bit, but that's a bit more than usual, and I wasn't even on morphine.

I traced everything from the pins to whatever input or output  (switches or lights) devices were attached, and almost all of it seemed to do something. The three adjustable gizmos (pots) in the top right are not connected, but I looked at my code, and worked out what they should be connected to (they adjust food amount, total food allowed in a day, and light sensitivity to trigger the dawn reset.

There are also these four resistors that dont seem to do anything.

I'm guessing they are either, connected to the potentiometers (adjustable gizmos) or have something to do with the second circuit that I found.

The second circuit looks like this, and I'm pretty sure it was meant to be mounted like this.

It has a button and a switch.

I remember making a water proof override switch so I could give the fish a dose of food when I visited them and wanted to see them hit the demand lever and get fed.

Now the four resistors might be for the pots, but I cant remember if they needed resistors. They are, after all, resistors.

I think.

But some things need resistors so they don't feed ambient static into the chip, and give false readings that look like button presses or whatever.

Who knows, but it feels a bit like I'm almost, right on the edge of nearly being back on track.

120 things in 20 years Aquaponics - Digital demand fish feeders are sometimes better off recycled and started from scratch.


  1. Hello,
    I am looking to build a demand fish feeder for my college's aquaponics system and have your blog very helpful. I was wondering if you possibly could give me advice on where to start with gathering materials and creating a design.
    Thank you very much!

  2. If you are willing to put an amount of feed into a hopper that the fish can take at will without overloading the system, ie one days worth, then the easiest way is to buy a geared down motor from a hobby or electronics store and just attach it directly to a large drill bit and then to a switch in the water. If you search this blog in the search thinggy on the right under the first ad for the term "demand feeder" you will find a lot more info.

    Or look me up on (I'm BullwinkleII)

    There's also a thread on that forum about the project ...

    Good luck :)

    I'm happy to help in any way I can


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