What to buy, and what it costs.
The controller is the same for every room. The fan, the fogger and the cooling are not — they follow from how much air your room holds and how much substrate is respiring in it. Give it those two numbers and it will size them, because a grower asked to pick a humidifier from a marketplace listing buys the one that comes up first and then cannot hold 88%.
What this room needs
Two design conditions, and they point opposite ways. On a hot dry day — 35 °C at 25% humidity — ventilation carries about 0.70 litres of water an hour out of this room, which is what the fogger has to replace. During the monsoon the same ventilation brings roughly 2.08 litres an hour *in*, because air at 30 °C and 80% holds more water than your room does at 18 °C and 88%. A coastal farm needs a dehumidifier that an inland farm does not, and no amount of fogger solves it.
The node
| Part | Qty | Rupees | Why this one |
|---|---|---|---|
| ESP32-S3 DevKitC-1 (N16R8) The controller. Dual core, 16 MB flash, enough room for the 72-hour reading buffer. |
1 | 950 | The S3 rather than the original ESP32 for the flash, which is what lets the node keep three days of history through a hub outage. |
| Sensirion SCD41 breakout CO2, photoacoustic NDIR. The measurement the whole crop turns on. |
1 | 3,200 | A third of the build. Cheaper MH-Z19 modules exist and drift badly above 90% RH, which is every hour of a mushroom crop. Do not run its automatic self-calibration: it assumes the room sees 400 ppm weekly, and a grow room never does. |
| Sensirion SHT41 breakout Air temperature and humidity. |
1 | 750 | Rated to condensing. Mount it in a vented shield out of the mist path — a sensor hit by fog reads the fog, and the controller then does the exact opposite of what the room needs. |
| DS18B20 waterproof probe Substrate and compost temperature. |
2 | 360 | Two, not one. The redundancy is the point: on a disagreement beyond 2 C the node holds last-known-good and alerts instead of acting on a lie. Mandatory for Agaricus, where compost temperature is the control variable and air temperature is not. |
| BH1750 light sensor Lux. |
1 | 120 | Cheap, and it verifies that the light channel actually did something. A failed LED driver is otherwise invisible until the pinset fails. |
| 8-channel opto-isolated SSR board Switching. Solid-state, not mechanical. |
1 | 1,400 | Solid-state is not a preference here, it is arithmetic. The fogger channel switches around a million times a year at fruiting duty; a mechanical relay rated for 100,000 operations is finished in five weeks. |
| Mains SMPS, 5 V 3 A, enclosed Power. |
1 | 450 | Enclosed, not an open board. This lives two hundred millimetres from a fogger. |
| DS3231 RTC with battery Clock across a power cut. |
1 | 150 | Without it the node cannot tell a two-minute brownout from a nine-hour outage, and so cannot decide whether to resume the stage or ask. That decision is the difference between a recovered crop and a lost one. |
| Three-position switches, OFF/AUTO/ON Manual override, per critical channel. |
4 | 360 | Wired so ON bypasses the relay logic entirely. Growers do not trust a box they cannot override by hand, and they are right not to. |
| IP65 enclosure, 200x150x75, with glands The box. |
1 | 850 | A grow room is a 90% humidity environment with mains inside it. The barrier between the low-voltage and 230 V sections goes in here. |
| Terminals, fuse holder, earth bonding, cable The unglamorous half. |
1 | 600 | Fused and earthed. This section is what a licensed electrical engineer has to sign off before anything is sold. |
Rs 9,190 at 2026-08 retail, against a Rs 9,000 target — over by Rs 190. The CO2 sensor is Rs 3,200 of it, 35% of the build, and it is where the target goes. A cheaper NDIR module would bring it comfortably under, and every cheap one tested drifts badly above 90% humidity, which is every hour of a mushroom crop. Sourcing a credible cheaper part is the single change that would most move this price.
The room
| Part | Qty | Rupees | Why this one |
|---|---|---|---|
| 150 mm inline duct fan, ~350 m3/h Exhaust |
1 | 2,600 | |
| Passive intake with insect mesh Make-up air. A room with no intake cannot exhaust. |
1 | 400 | |
| Ultrasonic humidifier, 1.5 L/h, 6 L tank Humidity |
1 | 2,200 | |
| Circulation fan, 200 mm Mixing. Every number this module reports assumes a well-mixed room; without a circulation fan the sensor reads one corner of it. |
1 | 900 | |
| Dehumidifier / small cooling unit, ~600 W Cooling |
1 | 12,000 | |
| LED strip, 4000 K, with driver Light. Cheap, and the smallest line on this list. |
1 | 700 |
Rs 18,800 for the room hardware. This is the larger number and the one growers underestimate: the controller is a tenth of the cost of the plant it controls.
Before you wire any of this
The 230 V section goes behind a physical barrier, fused and earthed, inside an IP65 enclosure with proper glands, and it must be separated from the low-voltage side rather than merely tidy. Mains switching for anything inductive or above 10 A — inline duct fans, compressors — goes through contactors, not relays. If you intend to sell a built unit rather than run your own, have the mains section reviewed by a licensed electrical engineer and budget for BIS testing. This page is a parts list, not an electrical design.