Range Logic, Multiple Sensors & Threshold Windows

Week 27 Term 4 45-60 minutes

Learning Objective

Use AND/OR logic in two ways: test one sensor against a range, or combine conditions from two different sensors. Build stable threshold windows and smarter rules that react only when the right combination of real-world conditions is present.

Theory: Building a Comfortable Zone

The Problem with One Rule

Last week's nightlight turned On in the dark. Turning it Off again needed a second rule.

The Danger: Rapid Switching (Jitter)

If both rules switch at one value, like LDR = 50, a wobbling reading (49, 51, 50, 48, 52) is a problem. The LED flips on, off, on, off every second or two, each time a new reading crosses the line. This flicker is called Jitter. It quickly wears out a relay and the fan or heater it controls.

The fix is a gap between the ON value and the OFF value, called a Threshold Window.

Real-World Example: The Smart Incubator

Baby chicks must stay warm, but not too hot.

Rule 1 (Too Cold):   If Temp < 20°C → Relay On (Heater ON)
Rule 2 (Too Hot):     If Temp > 26°C → Relay Off (Heater OFF)
✅ In-between zone: 20 °C to 26 °C. Neither rule runs, so the heater keeps doing what it was last told: still heating on the way up, still off on the way down.

This 6°C gap keeps the system stable.

For Teachers

This is Hysteresis, made simple. If both rules switched at 25 °C, the relay could click on and off every few seconds and soon wear out.

The Built-In Range Logic

A single rule can make a window too. Just under the Sensor, Operator and Threshold boxes in the Loop Condition panel, tick Use Range.

Now Range Logic (AND / OR), Operator 2 and Threshold 2 switch on, so the rule tests the sensor twice.

The Use Range controls in the Rule Engine: Range Logic AND/OR, Operator 2 and Threshold 2

Tick Use Range (highlighted) to unlock Range Logic, Operator 2 and Threshold 2.

Range Logic means one sensor, two tests. Both watch the same sensor. For a different one, use Add a second sensor.

New: Combine Two Different Sensors

Ticking Add a second sensor adds a condition for another sensor. The two results are joined with AND or OR to decide whether the steps run.

Condition 1: Light Level < 40
How should the two sensor conditions work together? AND (Both must be true)
Condition 2: Motion Sensor == True
Result: (Light < 40) AND (Motion == True)

Set the first Sensor, Operator and Threshold.
Tick Add a second sensor. Its panel opens.
Under How should the two sensor conditions work together?, choose AND or OR.
Choose the Second sensor, its Operator and its Threshold.
For a window on the second sensor, tick Use second sensor range and set its second test.
Add the steps and save. The rule repeats while the result is true. If it turns false mid-cycle, MakerBuddy finishes that cycle, then stops.

The updated Add a second sensor panel with AND and OR combination options

Tick Add a second sensor, then pick AND (both true) or OR (either true).

The updated Use second sensor range controls

Ticking Use second sensor range gives the second sensor two tests too.

AND — both environments must agree

Every condition must be true. A security light needs dark and motion.

Dark AND Motion → LED On

OR — either sensor can trigger

Either danger is enough: high gas or a dangerously high temperature.

Gas High OR Temperature High → Alarm

Power-user pattern: give each sensor its own range. (Temperature > 20 AND Temperature < 30) AND (Humidity > 40 AND Humidity < 60) runs only when both are in their comfort zones.

AND makes a window. OR makes an alarm.

One small choice changes the meaning:

AND — inside the window

Both tests must be true: values between two numbers.

Temperature > 20 AND Temperature < 30

Runs only between 20°C and 30°C: a "conditions are good" light.

OR — outside the window

Either test is enough: values outside two numbers.

Temperature < 20 OR Temperature > 30

Runs when too cold or too hot: a "something is wrong" alarm.

So Which Should You Use?

It depends on how many different actions you need. One rule has one step list.

You want to…	Build it as…	Why
Do one thing while a value is in a band	One rule, Use Range + AND	One action needs only one rule.
Do one thing when a value leaves a safe band	One rule, Use Range + OR	One alarm covers too low and too high.
Do different things at each end (heat vs. cool)	Two separate rules	Two actions need two step lists.
React to two different sensors	One rule, Add a second sensor + AND/OR	Both results drive the same steps.

For Teachers

This is students' first real boolean logic (true/false logic). Act it out: have students stand up only when both statements are true, then when either is. Watch for > 30 AND > 20: it just means > 30.

Try It: Build Range and Two-Sensor Rules

Interactive demo · no kit needed

Play with a pretend MakerBuddy board and its web page, right here.

Follow the steps one at a time. Got the kit? You can switch to the real board inside.

Activity: The Climate Controller

Keep the room comfortable, with the RGB LED as a signal: Red = Heater, Blue = Air Conditioner.

Step-by-Step Instructions:

Rule 1 — Too Cold (Heater): Create a Condition rule named "TooCold". Sensor → Temperature (DHT11), Operator → <, Threshold → 22. Step 1: Action → RGB Red, Delay → 100 ms. Save.
Rule 2 — Too Hot (AC): Create a Condition rule named "TooHot". Sensor → Temperature (DHT11), Operator → >, Threshold → 28. Step 1: Action → RGB Blue, Delay → 100 ms. Save.
The Comfortable Zone: At 25°C both rules are false, so nothing changes.
Test it: Read the Temperature (DHT) card (0.0 means the DHT11 is not being read). Set TooHot's threshold 1–2 °C above that reading, then cup the DHT11 in your warm hands for half a minute. The RGB turns blue. Then set TooHot's threshold back to 28, ready for Part B.

Why two rules here? Two different actions, red and blue, need two rules.

Part B — The Same Job with One Rule

A green "conditions are perfect" light needs one action, so one rule with Use Range is enough.

Create a Condition rule named ComfortZone.
Sensor → Temperature (DHT11), Operator → >, Threshold → 22.
Tick the Use Range checkbox.
Range Logic → AND, Operator 2 → <, Threshold 2 → 28.
Step 1: Action → RGB Green, Delay → 100 ms. Save.
Test it: between 22 and 28 the light turns green. Warm the sensor past 28. ComfortZone stops, but green stays: a stopped rule never undoes its last step. A saved TooHot rule turns it blue.

That is Temperature > 22 AND Temperature < 28: a threshold window in one rule.

Part C — A Two-Sensor Security Light

Build the Week 20 smart-home flowchart: light on only when someone is there and it is dark.

Create a Condition rule named SecurityLight.
First sensor → Light Level (LDR), Operator → <, Threshold → a number halfway between your covered and room readings (for example 40).
Tick Add a second sensor. Under How should the two sensor conditions work together? choose AND (Both must be true).
Second sensor → 🏃 Motion Sensor. The Operator switches to Equal to (==) by itself and the box below becomes Value: choose True. (No Value list on an older dashboard? Choose Equal to (==) and type 1, meaning True, as the Threshold.)
Step 1: Action → LED On, Delay → 100 ms. Save.
Test all four mixes of bright/dark and motion/no motion. Only dark with motion should run the rule.

Remember: this rule only turns the LED on. Add another rule to turn it off.

Challenge: The Ultimate Nightlight

Fixing Last Week's Bug

Last week's nightlight never turned off. Fix it with two rules:

Rule 1 (Lights Off!): Sensor → 💡 Light Level (LDR), Operator → Less than (<), Threshold → 40. Step: Action → 💡 LED On, Value → 255, Delay → 100 ms.
Rule 2 (Morning!): Sensor → 💡 Light Level (LDR), Operator → Greater than (>), Threshold → 60. Step: Action → 💡 LED Off, Delay → 100 ms.

Tip: still flickering? The reading is wobbling across one of your two numbers, so widen the gap between them.

Question: Why 40 and 60, not one number for both? What if both used 50 and the reading wobbled between 49 and 51?

Bonus — the OR alarm: make one Condition rule that beeps when the room is too cold or too hot. Tick Use Range, select OR, then test Temperature < 18 first and Temperature > 30 second. Steps: 🔊 Buzzer On with Delay 200, then 🔇 Buzzer Off with Delay 800, so it always ends quiet. (Beeps in a normal room? 0.0 on the Temperature (DHT) card means the DHT11 isn't being read.) Why would this never work with AND? Tell a partner.

Coming Up Next Week:

Week 28: Smart Safety Systems: MQ-2 Gas Alerts

Learning Support

Use this quick guide to help every learner understand, practice and explain Range Logic, Multiple Sensors & Threshold Windows.

For students

Try it in three steps

Say it: explain the main idea in one simple sentence.
Show it: Build a temperature comfort range and a motion-plus-darkness security light.
Stretch it: Fix last week's nightlight with an ON rule below 40 and an OFF rule above 60, then build a one-rule OR alarm for too cold or too hot.

Checkpoint: What was your input, what decision or process happened, and what was the output?

For teachers & parents

Coach without taking over

Before: ask the learner to predict what will happen and why.
During: use prompts such as “What changed?” and “What could you test next?” instead of giving the answer.
After: ask for a 30-second explanation, one piece of evidence and one improvement.

Look for: safe handling, correct vocabulary, a result the learner can demonstrate, and an explanation in their own words.

Safety reminder: Plug the DHT11 and the PIR in only while the USB cable is unplugged, and never force a plug. Warm the DHT11 with your hands only, never a hair dryer, heater or flame. The heater-and-relay example is theory only: if you try it, use only the kit's low-voltage lamp or fan, never mains electricity.

Did you get it?

Three quick questions. Pick an answer to see whether it is right, and why.

1What is jitter, and what causes it?
2What does a threshold window (a gap between the on and off values) do?
3A rule should run when the room is dark AND motion is detected. When does it run?