Sensor to measure distance on inverted pyramid filled with maize

I'm struggling with the following problem:

I have an inverted pyramid, supported in four points, filled with maize up to 600KG.

I want to keep track of the level of maize inside the inverted pyramid.

I've thought about using a load cell but this can be expensive and I need a cheap solution to implement. I also thought about using a sensor centred on top of the inverted pyramid.

The problem here is that I really dont't know what kind of sensor can be used to get correct values. Can ultrasonic sensors give me bad values? The pyramid form is tricky...

PS: Theoricly can mill be too reflective and influence the result of measures?

I'm sorry for the English :P. I'm still learning.

If anyone can help I really appreciate.

Best Regards

• About what size are we speaking here? Commented May 26, 2018 at 18:54
• are you talking about the whole ears of corn or just the seeds? Commented May 26, 2018 at 18:55
• The pyramid has 1.80 m of height and at the top (inverted pyramid) is 2m. Commented May 26, 2018 at 19:00
• @jsotola It's just the seeds to be ground (milled?). Commented May 26, 2018 at 19:02
• i am guessing that the "inverted pyramid" is a funnel, so there is a discharge port on the bottom .... i wonder if a large rubber ball would "float" on top of the seeds ... if it does "float", then you could monitor its position somehow, but you would have to keep it out of the discharge port Commented May 26, 2018 at 19:02

The surface of corn is hard enough to reflect sound from an ultrasonic sensor. It reflects from fabric, skin and of course, plastic, and corn fits into the realm of reflectivity.

An Arduino with an ultrasonic sensor may scatter a good bit of the reflection, but some of it will get back to the receiver in sufficient condition to be registered.

The components necessary to test this are low enough cost to suggest a prototype. A simple pail or bucket filled with the grain and attached to a rope and pulley will give you distance information, and that would be for a relatively small surface area.

Ultrasonic sensors typically have a minimum distance and of course, a maximum distance. If your concern is for both full and empty conditions, dual sensors placed a sufficient distance apart with suitable range considerations are likely to work. The code would be written to avoid cross-pulse readings, which is likely to be trivial, as these devices operate at the speed of sound.

Lasers are point devices and may not necessarily reflect to the sensor for reading.

I have constructed a DME (distance measuring equipment) that displayed passing vehicles within a range of ten feet (~3 meters) down to slightly less than three feet (<1 meter) with good results. There was tremendous lag in the reading, but that's due to code ignorance, not hardware problems. I suspect the depth finder is not going to have much lag in determining its value to this application.

• And dust can give me bad values? Commented May 26, 2018 at 21:08
• I'll bet if you have enough dust to make visibility difficult, it would give you very short readings on the ultrasonic or none at all. It's not out of the question that the ultrasound would be absorbed by small enough dust particles. I'm aware that some grain silos have explosion danger due to dust. The cost is still low enough to justify a test build, even if only in breadboard form. Commented May 26, 2018 at 23:39

You can let the sensor "sense" 20 times and let your Arduino figure out the average. More on Using the HC-SR04 Ultrasonic Distance Sensor with Arduino.

Maybe the ultrasound also scares rodents. I am using IR sensor Sharp GP2Y0A02YK which reaches from 20-150 cm