DIY smart fan controller with JoyReef — Part 2: configuration and rules

Total time: about 20 minutes · Difficulty: Medium · Prerequisite: Part 1 completed

In Part 1 you wired the DS18B20 probe to the controller and plugged the fan into the smart plug. Now the portal needs to know two things: which probe reads your tank water, and which plug drives the fan. After that, a single rule is enough — not two.

Assign the probe to the controller

1. Log into portal.joy-reef.com
2. Go to Devices and open your controller
3. In the Controller configuration panel, under Temperature probe, pick the function Tank water (or Sump, if the probe sits in the sump)
4. Click Save configuration

Each function can be assigned to only one sensor: with two probes, one will be Tank water and the other Sump.

⚠️ Warning: if the temperature doesn’t show up within a couple of minutes, go back to the wiring in Part 1. The DS18B20 has three wires: red/VCC, black/GND, yellow/DATA.

Add the fan’s smart plug

If you have already paired a smart plug with the portal — for the ATO, for instance — the procedure is identical and you can skip to the next step.

1. Make sure the plug is powered and on your WiFi network
2. Go to the portal → Plugs and add the plug
3. Give it a recognisable name, for example “Fan”
4. Check that it shows up as online in the list

Create the rule: Automations → Temperature rules

Here’s the part that matters, and it’s simpler than it looks: you don’t need two separate rules for switching on and off. The portal has a dedicated temperature manager with hysteresis built in.

1. Go to Automations → Temperature rules
2. Turn on Enable control at the top
3. In the High temperature panel (“Turn on fans or chiller when above threshold”) press Enable
4. Fill in the panel:
   • Maximum threshold (C): 27
   • Hysteresis (C): 1
   • Sensor (opt.): the probe you assigned earlier — leave it empty and the controller uses its local probe
   • Chiller: select the “Fan” plug
   • State ON and State OFF stay as ON and OFF
5. Click Save settings: you’ll see “Temperature settings saved and sent to controllers”

💡 How it works: above the maximum threshold the chiller turns on and stays on until the temperature drops below threshold − hysteresis. With a 27.0 °C threshold and 1.0 °C hysteresis the fan starts at 27.0 °C and stops at 26.0 °C. Hysteresis is what stops it from cycling on and off constantly.

Why here and not in the free-form Automations

The portal also has an Automations section for free-form rules, and at first glance you could build two rules there: one turning the plug on above 27 °C, one turning it off below 26 °C. It works, but it’s the worse route.

• Hysteresis is a single field here, instead of two rules you have to keep in sync by hand
• The page shows live actuator status and the target range on the thermometer
• Temperature safety checks stay active
• On updated controllers the plug also gets a safety timeout: if the controller loses its connection to the broker, the fan won’t stay on indefinitely

Rule of thumb: heater and fan/chiller belong in Automations → Temperature rules. Free-form Automations are for everything else.

Check the dashboard

Go back to the tank dashboard. You should see:

• 🌡️ Real-time temperature with the historical chart
• 🔌 The “Fan” plug status (on/off)
• ❄️ On the Temperature rules page, the target range on the thermometer and the Chiller tile lighting up while the fan runs

👉 Next part: Part 3 — Testing, maintenance and optimisation

No controller connected to the portal yet? The JoyReef beta is free and open: portal.joy-reef.com/beta

JoyReef Guide · Part 2 of 3 · v1.1 · Questions? Write to supporto@joy-reef.com