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Comment by tomhoward | Hacker News Reader

Well I already have a firmware version that can run in a few KB, which my father developed in Motorola assembly and that ran most of the soil moisture monitoring devices sold to the big-volume wine grape producers in Australia (mostly in Riverland SA supplying Treasury etc) from the late 90s till about 2010, after which newer products using Zigbee and cellular IoT took over (though we worked together on our own newer versions supporting Bluetooth LE and Cat-M1 up until his retirement a couple of years ago).

I hear you that $20 is high - but the status quo in this business now is monitoring devices that sell for AUD $600+, and with LTE-M or LoRa comms modules that cost over AUD $60 alone.

I'm forever thinking about ways you could drive the cost down further. I'd love it if there were a way to get the on-plant modules under $1. Feel free to get in touch if you want to discuss further.

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BLE mesh and solar power should get your BoM cost below $20, but I don't see any way that you're going to hit a sub $1 price point. Assuming your mesh can cover the entire field (reasonable if you have one monitoring point every few plants), you can have one or a small handful of LTE-M basestation points to handle the data uplinks.

It's an interesting problem and I am sure reference designs already exist. Maybe talk to someone at Nordic.

Yeah I think that's right. It's a matter of trading off the water cost savings (and produce quality/yield gains) per plant vs unit cost per device, to determine the optimal density of devices.

As I said in the previous comment, right now, high-value crop growers like wine grape growers pay $700-$1000 or more per site (including reader/comms module and sensors), and generally only install one monitoring point per block (I have a system running at one of Australia's top boutique/biodynamic wine makers and at current prices he can only cost-justify having one 10 monitoring sites over his 70 acres of vines).

So, whatever we can do to drive down the cost to $20 or less should deliver big wins.

> Maybe talk to someone at Nordic

Yep, we're working with hardware engineers who are well connected to people at Nordic.

There's (relatively) lots of water in the Barossa Valley and it's worth growing a thirsty high value crop like grapes there. And even there the cost structure you say is unsupportable.

But the economics of farming in the Eyre Peninsula is quite different and they really have a water problem. From a food PoV these are the people we really need to help.

(I have family in both, not to mention in laws in Germany who also have a water problem...getting rid of it!)

Can you use mesh networking? A solar panel and an Esp32, with mesh networking might be cheaper than an LTE module on each device, at the cost of needing more devices.

Yep, mesh networking is the plan:

https://news.ycombinator.com/item?id=40740278

Why must the device be so cheap? Is the intent to have one serve each plant? Why can’t one serve many plants?

Yes, that’s how it’s done now, but it’s a matter of the precision vs cost tradeoff.

Right now it costs about $750-$3000 to set up each monitoring site, so growers can only afford to install a low number of devices per acre [1], thus a high number of plants per device. In that case you’re not optimizing to anywhere the specific requirements of each plant, you’re assuming (often falsely) that all the plants in that area have the same needs as the one you’re monitoring.

The lower the cost per device, the higher your resolution and precision of monitoring can be, and the more you can accurately provide for the specific needs of each plant.

[1] Very often that number is zero.

It seems very wasteful to me to have a lot of small devices sitting out in the elements, how resilient are they going to be?

Wouldn't a device that travels like a snail along a cable or something, while less glamorous than a self propelled (and navigating) device, deliver a reading for a whole line of plants every day without all of the eroding parts per plant?

It’s pretty normal to have devices out in the elements now, it’s just a matter of how many. Yes having a device on literally every plant will probably always be overkill, unless they are so cheap and easy to replace that it doesn’t matter when one gets damaged. More likely it’d be optimal to have a device every x-number of plants - which is what’s done now but the number of devices per number of plants needs to be higher than is currently conventional to increase precision.

Having machines moving around taking readings “each day” is insufficient, as during hot conditions the soil/plant moisture changes too rapidly. You need to take readings at least once every hour or even every 30 or 15 minutes in order to be able to start irrigating immediately when the moisture level starts dropping rapidly.

For farming on a forest floor, I would expect overly complex variance.. For farming in a field, why isn't the deviance you calculate between the needs of plant location 1 & 2 on a frequent basis not a reasonable estimate to update the predicted needs of one plant every time you pass over the other?

I can imagine that a lot of small devices becomes economically viable.. I find that unfortunate since I think it will be a lot of permanent ewaste lost in fields relative to very temporary water optimization benefits.

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