Would it be sufficient to just have a cheap BLE pressure sensor that you could place underneath a potted plant and look for cyclical variations of pressure to determine when to water? I would think that any sensor in contact with the soil is going to have a much shorter lifespan than one which is kept dry and in a less reactive environment.
Yeah, this is my thinking, though I haven't built a proof of concept yet.
Load Cell Weight Pressure Sensors are AUD$5 or so, and I reason a shallow receptacle of sand sitting outdoors, where rain can fall in, and direct sunlight can slowly evaporate the water, should provide a sufficiently accurate analogue for soil moisture.
Certainly I would expect it would be easy enough to calibrate, using different depths of the medium, different types of medium (coir, perhaps), etc. An upside-down plastic pot saucer sitting under the tray would provide sufficient water-proofing for the pressure sensor, I'd expect.
Excess water drains out the bottom of potted plants. You'd need a coffee-scale style (e.g. Acaia Pearl) sensor, where the electronics are shielded from water from above. Those aren't cheap.
You can probably fairly easily average out the low-frequency pressure changes. Trivially, you can consider the minimum weight per week the weight of the plant, and calculate the difference based on that.
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Would it be sufficient to just have a cheap BLE pressure sensor that you could place underneath a potted plant and look for cyclical variations of pressure to determine when to water? I would think that any sensor in contact with the soil is going to have a much shorter lifespan than one which is kept dry and in a less reactive environment.
Yeah, this is my thinking, though I haven't built a proof of concept yet.
Load Cell Weight Pressure Sensors are AUD$5 or so, and I reason a shallow receptacle of sand sitting outdoors, where rain can fall in, and direct sunlight can slowly evaporate the water, should provide a sufficiently accurate analogue for soil moisture.
Certainly I would expect it would be easy enough to calibrate, using different depths of the medium, different types of medium (coir, perhaps), etc. An upside-down plastic pot saucer sitting under the tray would provide sufficient water-proofing for the pressure sensor, I'd expect.
Excess water drains out the bottom of potted plants. You'd need a coffee-scale style (e.g. Acaia Pearl) sensor, where the electronics are shielded from water from above. Those aren't cheap.
You could put this below a saucer/pot stand which is fine for most houseplants. For outdoor projects it's going to have to be waterproof anyway.
What if the plant grows?
You can probably fairly easily average out the low-frequency pressure changes. Trivially, you can consider the minimum weight per week the weight of the plant, and calculate the difference based on that.