Fill level measurement of liquids and solids

Good day Sirs,

Currently i try to develop a system for my bin/container to exactly know how much space is still left in my container.
With the HC-SR04 i am able to measure the distance of the nearest object in the cone but i cant really get a meaningful measurement of the complete container. When i put the sensor on the side the sound bounces of the walls and destroy my measurements related to how close it is to the wall.
The distances could be 5 cm to 3 meters.
Now my problem: Due to the different fill levels (5 cm on the side and 3m in the middle) i cant really know if the container is really full or if i could fit in something in the middle or the sides.

The only thing came to my mind is to build a complete array of sensors which is not really what i want.

What i could already exclude from the list of ideas are moving parts (scanning with a motor).

Any ideas?

Thanks a lot!

A big red button next to the container: when someone throws something into the container, he can press the button if he judges that it is full :wink:

I think that you'd need quite a sophisticated setup of sensor to do this automatically. Maybe a Raspberry Pi with a webcam would be the easiest solution. Then you can view the image of the camera in your browser, or process it with some kind of deep learning / image recognition software if you really want it to be fully automated.
But I think you have to ask yourself the question if it is really necessary. What would be the advantage of having it automated?

How big? What material is in it? What other obstructions over the top? Can you give us a photo?

As you have discovered, this is a surprisingly hard problem. Often it is easier to measure the input and output flow and subtract them. Strain gauges on the legs can weigh the bin but keeping them calibrated is difficult. A pressure mat on the bottom can feel the pressure of the contents on the bottom but this won't work for abrasive material.

Laser distance scanning is good, except if there is dust.

Thanks for the answers guys,

Description:
Container is 8m long, 3m wide and 3m high. It contains all kind of materials (glass, construction waste, , it could even be filled with liquid but lets skip this for now :). The materials can be dusty.
Its a metal/plastic top.

Optical systems (IR, cam, ... ) cant be used due to dust and smudge on lenses.
There are commercial solutions available but they are very expensive and id rather build it myself.

Similar to this one:
http://www.micodan.dk/pictures_ed/largeclick_largeclick_SpecialContainere47[1].jpg

PieterP:
A big red button next to the container: when someone throws something into the container, he can press the button if he judges that it is full :wink:

We tried this, but we had many false positives due to people jokingly press the button.

The other options wont work due to different materials and their weight.

Is there a way to get a complete dotted map of the container with lidar(not considering dust)?