Digital Stealth Care · humidity
Humidity controller for grow rooms
A grow room does not need a humidity switch. It needs humidity held where the stage wants it, with fans, a dehumidifier and a humidifier working in order so they never fight each other. This is how Digital Stealth Care does that today.
45 to 50
per cent humidity the Flowering stage aims for, on the stage rail
1.2 to 1.4
kPa, the VPD target for the same stage
90
seconds until the humidifier plug switches itself off if the brain goes quiet
240
seconds until the dehumidifier plug switches itself off, the longest, to protect its compressor
What the room asks for
Humidity is set by stage, not by one number
Cuttings and seedlings want wet air, late flower wants dry air. A single setpoint is wrong for most of a grow, so DSC keeps a stage rail: temperature, humidity and VPD together for each stage. These are its defaults, and every row can be edited.
| Stage | Air °C | Humidity % | VPD kPa |
|---|---|---|---|
| Rooting | 24 | 75 to 85 | 0.4 to 0.8 |
| Germination | 25 | 70 to 80 | 0.4 to 0.8 |
| Seedling | 24 | 65 to 75 | 0.5 to 0.8 |
| Early Vegetative | 25 | 60 to 70 | 0.7 to 1.0 |
| Vegetative | 26 | 55 to 65 | 0.8 to 1.1 |
| Late (Push) Vegetative | 26 | 50 to 60 | 1.0 to 1.2 |
| Early Flowering | 25 | 50 to 55 | 1.0 to 1.2 |
| Flowering | 24 | 45 to 50 | 1.2 to 1.4 |
| Late Flowering | 22 | 40 to 45 | 1.3 to 1.5 |
| Final 48-72h Flowering | 21 | 35 to 45 | 1.4 to 1.6 |
| Dry Mode | 19 | 55 to 62 | 0.8 to 1.0 |
| Balanced dry | 17 | 58 to 62 | 0.7 to 0.8 |
| Slow dry | 15.5 | 60 to 65 | 0.6 to 0.7 |
The room follows the stage you set, not the strain. The hub also carries the same table, so a stage change stays sensible even with no brain. Strains only change the flowering time, the stage and the harvest window; see how stages and the harvest window work.
How DSC holds humidity today
Air first, then the appliances
The hub runs this in its own firmware, from sensors wired to it, and it is what drives the room today. The brain adds the sensors you bind and keeps the record.
01
Read honestly
Readings pass through per-zone offsets and clamps. A reading that fails them is rejected, not smoothed, and one that stops changing raises an alert.
02
Move the air
The intake and exhaust fans chase VPD and temperature all the time, so they are the first response to a room that is too wet or too dry.
03
Too humid: dehumidifier
If humidity stays above the top of the band by a margin, the hub asks for the dehumidifier. It waits at least a minute, never restarts it within three minutes of switching it off, and stops it once humidity is back under the band.
04
Too dry: humidifier
If humidity falls below the band, or VPD runs above its ceiling, the hub asks for the humidifier. It never does so while the dehumidifier is running, so the two cannot fight, and it rests between runs.
The hub asks and the brain switches the plug. DSC also checks that the appliance did something: a dehumidifier that runs without moving the reading raises a critical alert, and so does a plug whose state disagrees with the request.
The rung order and the waits are in the guide: the climate ladder, failsafe and reality gates. Targets and modes are on the Climate desk.
VPD
Humidity is only half of it
The same 50 % humidity is a different room at 22 °C and at 28 °C. Vapour pressure deficit (VPD) is how hard the air pulls water out of a leaf, so it ties temperature and humidity together. Every stage on the rail has a VPD range as well as a humidity range.
Air VPD and leaf VPD
A leaf runs a little cooler than the air around it, so leaf VPD is the more honest number. The brain works out leaf VPD from your canopy sensors with a leaf-to-air offset you can change in Settings (2 °C cooler by default), and marks a reading held or stale when it stops trusting it.
Check your own room
Type in your air temperature and humidity and the free VPD calculator gives leaf VPD, air VPD and the dew point, and the stage the reading suits. The sensor guide explains how DSC decides which readings to trust.
Tents and domes
A propagation dome is not a flowering tent
A cutting has no roots yet and drinks through its leaves, so a dome holds its air much wetter than a flowering tent: the Rooting stage asks for 75 to 85 % humidity and Flowering asks for 45 to 50 %.
A second, smaller tent has its own targets and its own humidifier rung in the ladder. When two tents share the room, one is the priority tent and wins the shared exhaust, so a wet dome does not drag the flowering tent with it.
Which humidifier or dehumidifier suits your space is a buying question; the get started page lists what to buy and in what order.
Smart plugs
Each appliance sits on its own plug
The humidifier and the dehumidifier each run from a Sonoff smart plug that starts off when power returns and switches itself off if it has not heard from the brain for its own time. The same rule covers the heater and the heat mat.
| Smart plug | Switches itself off after |
|---|---|
| Heater | 60 seconds |
| Heat mat | 90 seconds |
| Humidifier | 90 seconds |
| Dehumidifier | 240 seconds (4 minutes) |
The dehumidifier waits longest, to protect its compressor. A compressor dehumidifier also needs a plug or contactor rated for its switch-on surge: the read before you buy notes say how to check.
The supported devices page lists the humidifiers and dehumidifiers DSC recognises, by brand and by how they connect.
Failsafe
What happens to humidity when the brain stops
The brain is the Raspberry Pi that runs the dashboard, the plans and the logs. If it stops, the hub keeps running its wired fans and dimmed lamps from its own sensors and its own clock, inside its hard limits.
The hub cannot switch the smart plugs, so the humidifier and dehumidifier switch themselves off after their times in the table above and the fans carry on alone. Humidity then drifts until the brain is back.
A kit with no hub has none of this: no wired fans, no hard limits and no sensor-fault mode. We do not recommend running a room that way for the long term.
Two hard limits apply whether or not the brain is running. At 35 °C in the tent the hub runs the outside exhaust and both intakes at full, switches the room exhaust and the lamp off, and stops asking for humidity or heat. With no valid tent temperature for 3 minutes it stops asking for humidity and heat and runs the fans gently.
The full detail is in when the brain stops: the hub and the plugs. What runs today and what is coming is on the status page.
Measured, not just described
Why a plain humidity controller falls short
A relay controller switches a mister around one number and cannot see temperature, so it cannot hold VPD. We wrote up what that means in practice: a humidity controller is a thermostat, not a brain.
Every alpha build is free, this one included, and yours to keep. No account, no subscription, no licence check. Keep the image and you keep the software.