ESP-NOW sensors for fields without power or wifi
Out on a plot there is no socket and no wifi. An ESP-NOW satellite does not need either: it runs on a battery or a solar panel and sends its readings to a gateway that is online.
What an ESP-NOW satellite actually is
A satellite is a small measuring device, built on the ESP32 family, that you place where the crop is. It has no wifi credentials and no subscription of its own. It wakes up, reads whatever sensors are wired to it, puts the values in a packet of a few dozen bytes and broadcasts that over ESP-NOW, a radio protocol that sits on the same 2.4 GHz hardware as wifi but skips the whole network handshake.
That is why a satellite can live on a battery or a small solar panel for a long time: the radio is on for milliseconds at a time. And because it never joins a network, there is nothing to configure in the field. You power it up and it starts sending. Compare that with connecting a sensor to your wifi, which every wifi device has to go through first.
How a reading reaches your dashboard
Four steps, and only one of them needs a network.
The satellite measures
It reads its probes and builds one packet, with a separate channel for each measurement.
It broadcasts
No pairing, and no acknowledgment to wait for. If nothing is listening the packet is simply lost, and the next one follows at the next heartbeat.
A gateway picks it up
The ESP-NOW gateway is the one device in your setup that does have wifi. It collects the packets of every satellite in range and posts them to your FairGrow account.
FairGrow does the rest
Card, chart, history, alarms and automations all run on the same path as a Zigbee reading. A satellite is a device in your dashboard like any other.
One thing worth knowing about channels
A satellite only reaches a gateway that is listening on the same radio channel. The gateway takes the channel of the wifi access point it joins, so if your access point moves to a channel the satellites do not use, the readings stop arriving while both devices look perfectly healthy. FairGrow checks that for you and says so on the device card, naming the channel it found and the channel it expected.
What a satellite measures today
Every one of these we build and flash ourselves, on standard ESP32 silicon you can source anywhere.
Soil satellite
Soil moisture and soil temperature, with two or three probe pairs on one satellite, so you can read several depths or several beds from a single unit. See also how often a soil moisture sensor should measure.
Light and soil
A light sensor next to a soil probe, so you see light and moisture at the same spot. One version carries a small display that shows the current reading on the satellite itself, for when you are standing next to it.
Leaf wetness
A wetness plate that reports leaf wetness as its own kind of reading, with its own color in the chart and its own place in automations. The sensor also has a comparator output: the moment the leaf goes wet the satellite sends straight away instead of waiting for its next heartbeat. That moment is exactly what a disease model needs, so it matters for crop protection.
Pump and valve
A satellite that does not only measure but switches: a pump or a valve at no more than 12 V, with its state reported back, so you can see in the chart exactly when it ran and for how long.
The ESP-NOW gateway
The device that collects everything and talks to the platform over wifi. It measures on its own account as well, so a gateway is a datalogger too and not only a relay station.
New sensors keep coming
We keep working on new sensors. Sometimes because a grower needs something that does not exist yet, sometimes because a disease model asks for a reading nobody takes. If what you need is not in this list, tell us: that is how most of these started.
Industrial sensors without the industrial price
Because an ESP-NOW satellite needs no network stack and no subscription of its own, the hardware stays simple. That is what lets us design and build it ourselves, in an IP65 housing with industrial components, instead of buying a sealed product from someone else.
We build in small series in our own controlled environment. That is also what makes certification achievable at this scale: CE certification is planned for the middle of 2027. And it is what keeps the cost price down, so you get an industrial sensor without the price that usually comes with one.
Calibration happens on the platform, not on the satellite
A raw soil or wetness reading is a number from an analog input, and what counts as dry and what counts as wet differs per probe, per soil and per satellite. So the satellite sends the raw value and FairGrow does the conversion.
You set two points: what the sensor reads when it is dry and what it reads when it is wet. From then on the server calculates the percentage, and if you refine the calibration later it applies to your whole history and not only to new readings. There is a separate small offset for a sensor that sits slightly high or low, so you can nudge one without touching the two points.
Updating a datalogger out in the field
Firmware goes over the air, with one limit we would rather name than hide.
How it works
- The gateway relays the update command with a URL.
- The satellite streams the image straight from HTTP into its unused application partition.
- No SD card, no file system, no cable and no site visit.
- The update runs from the main loop, never from the radio callback, and any failure restarts the datalogger with the firmware unchanged.
One honest limit
- A satellite has no uplink to confirm itself with, so unlike a gateway there is no deadline that rolls a bad image back on its own.
- That is why every satellite build is tested on real hardware before it reaches the library.
What is coming
Named here so you can plan with it, and dated only where we are willing to be held to it.
PAR
A sensor for photosynthetically active radiation, the part of light a plant actually uses. Deliberately a separate sensor from the light satellite, because lux and PAR are different quantities and they are classified differently for customs and certification too.
Leaf wetness by infrared
We are developing a leaf wetness sensor built on an MLX90614 infrared thermometer. Instead of a plate that has to get wet itself, it reads the temperature of the leaf and compares it with the air, which is where condensation shows up first. CE certification for that sensor is planned for the middle of 2027.
LoRaWAN for longer distances
ESP-NOW carries a long way in open air, but not everywhere. For the distances it does not cover, LoRaWAN loggers are on our roadmap, together with support for the sensors that already use that protocol. LoRaWAN is an open standard on the 868 MHz band, so there too you will not have to buy from us.
Zigbee or ESP-NOW
Most growers run both, and everything lands in the same dashboard.
Choose Zigbee when
- The sensor sits near your house, greenhouse or gateway.
- You want to buy off-the-shelf hardware, see standard sensors without lock-in.
- A mesh of devices in between can keep the signal up.
- You want to use your own coordinator.
Choose ESP-NOW when
- There is no socket and no access point.
- The plot is beyond the Zigbee mesh.
- You want to switch a pump out in the field.
- You want the source of the device you are running.
Source code of the ESP-NOW sensors included
We invest in better firmware every week, and the source code of our ESP-NOW sensors comes with it, at no extra cost. No lock-in: your sensors are standard and your data stays yours. It is not a binary with a sticker on it but the sketch, under the MIT licence, so you can read what your sensor does before you trust it with a decision.
Questions we get
What is an ESP-NOW satellite?
A small self-sufficient measuring device that runs on battery or solar, needs no wifi and no SIM card, and broadcasts its readings to a FairGrow gateway that forwards them to your dashboard.
Do I need wifi in my field?
No. Only the gateway needs wifi. The satellites never join a network, which is also why there is nothing to set up on them out in the field.
How far does it reach?
Further than Zigbee in open air, and satellites can relay for each other, so several of them together cover a larger area. Walls, dense crop and metal all cost range, so treat any number you read anywhere as a starting point and measure your own situation. Ask through support if you want help planning a layout.
Why are my readings not coming in?
The most common cause is a channel mismatch between the gateway and the satellites. Check the device card: it names the channel it found and the channel it expected, and that is usually the whole story.
Can I use my own sensors?
Yes, within what a satellite supports, and you get the source code of the ESP-NOW sensors, so you can see where to add one. A channel that a satellite does not recognize arrives as a generic reading rather than being dropped, so you keep the data while the label catches up.
Does a satellite measure leaf wetness?
Yes, as its own kind of reading since the leaf wetness sensor, and you can hang an alarm or an automation on it. An infrared version built on an MLX90614 is in development, with certification planned for the middle of 2027.
Can I update a satellite myself?
Yes, over the air. The gateway passes the command along and the datalogger fetches the image itself, so a sensor out in the field never needs a cable.
Measuring where there is no socket
Tell us what the plot looks like and what you want to know from it. We will say which devices fit and which ones do not.