What did I learn by throwing a bottle into my water tank?

Follow along!

If you’ve ever stayed in a house, then there is this little annoying problem — you don’t know how much water is left in your overhead tank! It’s always annoying to find out that you’ve run out of water.

  1. It is expensive. Costs NRs. 7k just for the device, not to mention you will have to run wires from the top to the bottom of your house and other installation charges that you will always be salty about.
  2. This is more about the lessons I learned. What I made is pretty jank anyway. 🤣
If pictures can speak a thousand words, then a gif can certainly do better.
Certainly cheaper than anything else in the market, don’t you think?.

Alright, let’s quickly set this up

  1. Fill up the larger bottle with water up to 70% capacity.
  2. Toss the larger bottle inside the tank, keeping the smaller one outside.
  3. Fill up the smaller bottle until it starts to pull the larger bottle.
  4. Remove just enough water so that the larger bottle pulls back again.
The readout bottle is nearly at the bottom, which implies that water is almost full in the tank.
The probe bottle is at the near top of the tank, which matches the earlier observation

Please don’t tell me it works?

It works! But it isn’t without flaws. The most obvious one is friction in the system, and it slows down the readout system. When the tank cover is closed, this is what it looks like:

The tank cover has a crack in it, where I can slip by the thread and some extra equipment.

But seriously, what’s to learn from this junk?

  1. Before you start a project, always check on the internet if anyone has already solved the problem. I have cut out the over-complicated designs I had wasted several days thinking about, whereas this google search only took me about 5 minutes.
  2. Simpler systems are better — the fact that there is no electrical system, and it’s just gravity and buoyancy doing the work means that I don’t have to protect it from the sun, rain, wind, etc. This system is super easy to maintain, replace and operate!
  3. Shapes — put more effort into it! It changed the precision of the product!
  4. Thread quality needs to be researched, I’ve noticed that non-tangling headphones use a flatter wire…, that shape seems relatively immune to tangling.
    However, in this case, the flatter thread system would further increase the friction. Not to mention that I have no way to manufacture such a material.
    Additionally, the tangling occurs only during maintenance and does not cause issues during operations.
  5. While sending information from one location to another, the correctness decreases as the distance increases. In this project, had I increased the length of the thread, or added more anchor points, the readout would have been more inaccurate.
    This sounds very obvious, but I didn’t consider this a serious problem until very late into the testing, thinking I’ll figure something out along the way.
    I tried to use other alternate readout mechanisms, such as using sound, electrical signals, wifi, pressure, but regardless of the mechanism, it would get inaccurate by the time the information is observed 3 floors below where I typically stay.

Main takeaway

The major lesson to learn from this project is that if you want to have a monitoring system, then use something digital. And, by digital, I do not mean using fancy chips & computers, it is about using definite-discrete values instead of continuous analog values.



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Samridh Tuladhar

Samridh Tuladhar


A computer engineer, with a passion for cheap, affordable & environmentally friendly automation and utter disdain for paperwork and waiting.