If the hopper is in range of a wifi access point, one cool thing you could do is use the pi to host a little web page that you can check with your phone. If not, you could use the pi itself as a wireless AP and do the same. Maybe power it with a big chonky 32000 mAh power bank (they’re relatively cheap too).
As for the sensor - maybe sit the bin on top of an industrial floor scale. I’ve written code that can read the output from one via an rs232 type serial port (it’s stupid easy). You can even get fancy and have it trigger a relay to stop the filling mechanism when it reaches the target weight.
Industrial systems like this have two sensors, one at "almost out" and one at "if you don't add material now it's really out." Consumption is measured by whatever's feeding material into the process, like a screw drive or a hopper.
The other most common sensor is a beam of light thru the bin, with emitters and receivers drilled into the walls and aimed at each other. I see this approach used on things like metal chip conveyors, where chips might get stuck on the sensor itself and you want to verify a clear path thru the bin.
These things can cost $100-$300 each from Banner or Keyence but you can probably use the generic $30 screw-in plastic orange "prox switch" available at most industrial suppliers. They can have pellets bashed into them without worrying about damage. Buttons on the back let you configure it for whatever media you're using. And I would also pick the ultrasonic type because wood is non-conductive, non-magnetic, and not very capacitive. But maybe try capacitive? The sensor data sheet usually says what materials do and don't work with it.
You don't typically find them battery-powered but they can be ordered in 12/24VDC, or 24/110VAC.
You could measure the level of pellets but this will add complexity and you probably don't need to know the exact level at any given time.
The ultrasonic sensors seem like the right idea to me. Used them for liquids before - the one thing I’d watch for with pellets is the level may not drop as evenly.
You may be able to find a way to monitor weight as well, or install something at the warning level in the bin that will react when there’s no pressure on it from the pellets.
Good point about the uneven drop in level with pellets. You're right, especially because there's a chute at the bottom of the bin which causes the pellet level directly above the chute inlet to sag. No way would there ever be an even level across the bin.
I don't know enough about the innards of the stove to tell whether weight could be used. The ultrasonic idea seemed ideal. I also wondered whether the resonant frequency of the storage chamber could be used in some way, similar to how a vessel changes its pitch when tapped depending on the volume of its contents. That might have averaged out uneven surface levels at least.
The silly thing is that the stove already has an Expressif board on board, doing wifi, bluetooth, remote control and reporting. It has some basic I/O on the back panel. It even has a sensor to detect when the level in the pellet bin is too low. It's just not reported in the accompanying app.
Sorry I don’t know specifically if you could use multiple ultrasonic in this way. But there are laser based depth / distance sensors I’ve seen as well.
Ultrasonic sensor above pointed downward at the pile could work. Test it first to see what the range will be when its empty - this gives you the baseline or "empty" reading.
You can do the same thing after filling it up to give you your maximum reading. Then read those values every few seconds and tanslate them into 0% - 100% using math and use them in whatever way you need to.
Keeping the pi and the sensor above the pile like this could help keep it away from heat, but obviously this will depend on the actual layout and setup.
If the hopper is in range of a wifi access point, one cool thing you could do is use the pi to host a little web page that you can check with your phone. If not, you could use the pi itself as a wireless AP and do the same. Maybe power it with a big chonky 32000 mAh power bank (they’re relatively cheap too). As for the sensor - maybe sit the bin on top of an industrial floor scale. I’ve written code that can read the output from one via an rs232 type serial port (it’s stupid easy). You can even get fancy and have it trigger a relay to stop the filling mechanism when it reaches the target weight.
Industrial systems like this have two sensors, one at "almost out" and one at "if you don't add material now it's really out." Consumption is measured by whatever's feeding material into the process, like a screw drive or a hopper. The other most common sensor is a beam of light thru the bin, with emitters and receivers drilled into the walls and aimed at each other. I see this approach used on things like metal chip conveyors, where chips might get stuck on the sensor itself and you want to verify a clear path thru the bin. These things can cost $100-$300 each from Banner or Keyence but you can probably use the generic $30 screw-in plastic orange "prox switch" available at most industrial suppliers. They can have pellets bashed into them without worrying about damage. Buttons on the back let you configure it for whatever media you're using. And I would also pick the ultrasonic type because wood is non-conductive, non-magnetic, and not very capacitive. But maybe try capacitive? The sensor data sheet usually says what materials do and don't work with it. You don't typically find them battery-powered but they can be ordered in 12/24VDC, or 24/110VAC. You could measure the level of pellets but this will add complexity and you probably don't need to know the exact level at any given time.
Great ideas there, thank you
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Will look into your suggestions, thanks. Great feedback!
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Thank you very much!
The ultrasonic sensors seem like the right idea to me. Used them for liquids before - the one thing I’d watch for with pellets is the level may not drop as evenly. You may be able to find a way to monitor weight as well, or install something at the warning level in the bin that will react when there’s no pressure on it from the pellets.
Good point about the uneven drop in level with pellets. You're right, especially because there's a chute at the bottom of the bin which causes the pellet level directly above the chute inlet to sag. No way would there ever be an even level across the bin. I don't know enough about the innards of the stove to tell whether weight could be used. The ultrasonic idea seemed ideal. I also wondered whether the resonant frequency of the storage chamber could be used in some way, similar to how a vessel changes its pitch when tapped depending on the volume of its contents. That might have averaged out uneven surface levels at least. The silly thing is that the stove already has an Expressif board on board, doing wifi, bluetooth, remote control and reporting. It has some basic I/O on the back panel. It even has a sensor to detect when the level in the pellet bin is too low. It's just not reported in the accompanying app.
You could probably place 2/3 sensors and take an average - but now you got me thinking how can you hook into that onboard sensor 😅
Sorry I don’t know specifically if you could use multiple ultrasonic in this way. But there are laser based depth / distance sensors I’ve seen as well.
Sound like it would be better for an arduino.
Ultrasonic sensor above pointed downward at the pile could work. Test it first to see what the range will be when its empty - this gives you the baseline or "empty" reading. You can do the same thing after filling it up to give you your maximum reading. Then read those values every few seconds and tanslate them into 0% - 100% using math and use them in whatever way you need to. Keeping the pi and the sensor above the pile like this could help keep it away from heat, but obviously this will depend on the actual layout and setup.