What a node is made of

The short version

A station is a sealed plastic box on a riverbank containing a microcontroller, a handful of sensors, a 4G modem and an SD card, powered by a solar panel through a Victron charge controller. It wakes on a schedule, takes a reading, writes it locally, uploads it when it can, and goes back to sleep.

The board

~£185–220
182 × 136 mm, two layers, 67 parts. Controller, modem, clock, sensors, SD card, power switching and a full surge protection chain on everything that leaves the box.

The power system

~£120–200 + battery
Panel, MPPT controller, fuses and mounting. The battery is chosen per site.

The box and the rest

~£80–130
Enclosure, glands, vent, antenna, temperature probes, padlock.

One station, excluding the battery: roughly £385–550. The battery is the widest variable and deliberately sits outside that range — see Choosing the right node.

On the board

Every module sits in a socket rather than being soldered down. That is not neatness — it comes from the first prototype, where the power supply, the microcontroller and the modem were each suspected dead and all three turned out to be fine. A socketed module comes out in seconds for bench testing.

Modules, all socketed
Part	What it does	Cost
Waveshare ESP32-S3-Pico	The controller. Also the Bluetooth radio that receives Victron telemetry.	£9.60
Waveshare SIM7600G-H 4G module	LTE Cat-4 upload path with a 2G fallback. A node without one still logs to SD.	£64.40
Adafruit DS3231 RTC	Timekeeping, and the alarm that wakes the node.	£16.80
Adafruit BME280	Enclosure climate and the barometric reference.	£14.40
microSD module	The primary log. Uploads are a convenience; the card is the record.	£7.30
INA226 current monitor	Fitted, but no longer read — see below.	£8.20
5V buck converter	12 V down to 5 V for the controller.	~£3–5

One module is fitted purely to complete a circuit. The INA226 used to measure battery current. It does not any more — the Victron controller reports that over Bluetooth, and the firmware stopped reading the chip. But it sits in series in the 12 V supply: everything downstream is fed through its measurement shunt. Removing it would not degrade the station, it would switch it off entirely. So it stays, and its socket is a candidate for a different sensor later — with a link fitted across the two power pins.

Power switching, protection and passives

The node spends most of its life asleep, so it switches its own supplies off rather than leaving them idling.

12 V switching — two FQPF47P06 P-channel MOSFETs: one as reverse-polarity protection on the input, one gating the modem. The modem pulls up to 2.2 A in transmit bursts, which is why the 12 V track is 1.5 mm wide and why the board has to be made in thicker-than-default copper.
Sensor rail — an AP2281 load switch, the only surface-mount part on an otherwise entirely through-hole board.
Protection on the supply — a P6KE18A transient suppressor. 18 V, not 16 V: a lithium pack sits at 14.6 V on absorption charge and a 16 V part would clamp in normal use.
Bulk capacitors — 470 µF at the modem and 220 µF on the input, for those transmit bursts.
29 resistors and 10 capacitors, all through-hole. Commodity parts, about £10 for the set. They are also the reason the board is 182 × 136 mm, and the next revision converts them to surface mount to shrink it.

Keeping lightning out of the box

Two temperature probes go into the river on cables. Anything on a cable outside the enclosure will eventually take a surge, so each probe gets a four-stage chain before its signal reaches the controller.

Stage	Part	What it handles
1	Gas discharge tube, 90 V	The strike itself — it short-circuits the surge to ground.
2	Resettable PTC fuse	The follow-on current after the tube fires. Resets itself; no field visit.
3	220 Ω series resistor	Limits what reaches the microcontroller pin.
4	Schottky clamp pair	Holds the signal between ground and the supply rail.

Earlier prototypes had none of this. It is the single biggest reliability change in the current design, and it is why the parts count went up rather than down.

Power

All station equipment runs from the charge controller's load terminals — nothing connects directly to the battery. The controller reports battery voltage, current and solar yield over Bluetooth.

Part	Notes	Cost
Victron SmartSolar MPPT 75/10	Charge controller and telemetry source in one. Bluetooth built in. UK stockist.	from £48
Solar panel, 12 V	20 W minimum for a standard station; 30 W minimum if a camera shares the supply.	~£48
Battery and BMS	Sodium-ion with a custom Victron profile is the recommended starting point. Capacity follows the site survey.	per site
Fuses, holders, panel mount	One fuse per load off the battery bus.	~£25–35

There is no recommended battery capacity, and that is deliberate. Usable energy depends on the chemistry's permitted operating range, the temperature, the panel's winter output at that specific site and how many sunless days the station has to ride out. Two rules hold regardless: confirm the pack and its BMS are compatible with the controller, and set the charging profile from the battery manufacturer's own specification rather than a generic one. Recording the battery in RiverNode documents it; it does not configure the charger.

Sensors, radio and enclosure

Part	Notes	Cost
Waterproof DS18B20 probes ×2	River temperature and shielded air temperature. Which probe is which is assigned at commissioning, not by which socket it uses.	£7.00
Radiation shield	Stacked-plate, bought or 3D printed. Without it the air probe reads the sun, not the air.	£0–25
External 4G antenna + mount	Coverage at these sites is patchy. The modem's own stub antenna is not adequate; get it outside the box and high.	~£6
Plastic ammo box	Plastic, not steel — a metal box would block both the antenna and the Bluetooth link to the controller.	~£15–25
Cable glands, vent, desiccant	A pressure-equalisation vent keeps damp out and is also what makes the internal pressure sensor a valid barometric reading.	~£20–35
Reed switch, magnet, padlock	Service mode is entered by holding a magnet against a marked spot outside. The box stays locked; there is no external button or port.	~£20

Buy one temperature probe before buying four. Inexpensive probes are often sold as "DS18B20-compatible" rather than genuine, and RiverNode's driver is deliberately strict — it validates two separate checksums, verifies the settings it writes back, and rejects probes that cannot be powered properly. Clones fail those checks more often. Test one before committing to a set.

Room left for later

A dissolved-oxygen and conductivity block was designed and then cut before manufacture — it was 19 parts serving a probe that has not been bought. What survives is the cheap part of that decision:

Five spare controller pins brought out to a header, alongside switched 3.3 V and ground, so a future sensor does not need a new board.
A spare module socket — the INA226's, once a link is fitted across its power pins.
A jumper for strong pull-up on the temperature probe bus, for probes that need more current during a reading.

Deliberately not on this list: pH probes (constant drift, and the rivers here are carbonate-buffered to a nearly flat reading), cheap optical turbidity sensors, and river level or flow hardware — the Environment Agency's own gauges already cover that and appear on the dashboard.

What one station costs

Group	Cost
Board, modules and fabrication	~£185–220
Panel, controller, fuses and mounting	~£120–200
Probes, SD card, radiation shield	~£15–40
Antenna and SIM hardware	~£10
Enclosure, glands, vent, lock	~£55–80
One station, excluding battery and data tariff	~£385–550

UK prices as read on 10 September 2026, mixing VAT-inclusive retail listings with trade prices quoted excluding VAT. Treat the range as a planning figure, not a quote. This page describes the current manufactured design; it does not claim every station in service is built to this exact specification — see “About This Station” on the dashboard for the hardware recorded against a particular node.