Handle Failed Reads
Detect NaN and retry without crashing.
Handle Failed Reads is a free Arduino & IoT Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Arduino & IoT Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Reads Can Fail
Even a good sensor sometimes returns nothing useful. Loose wires, fast polling, or noise can cause a failed read, so plan for it. ⚠️
Meet NaN
When a read fails, the library returns NaN, which means Not a Number. It is the sensor's way of saying I did not get a value.
Why NaN Is Tricky
A NaN never equals anything, not even itself. So you cannot just compare it with a normal number to catch the error.
Detect It with isnan
Use the built-in isnan() function to test a reading. It returns true when the value is the failed NaN result.
if (isnan(t)) {
}Check Before You Use
Always test a reading before you print or act on it. Skipping this check lets bad data slip into your logic unnoticed.
Check Both Values
Guard temperature and humidity together, since either can fail. If one is NaN, treat the whole reading as bad and skip it.
if (isnan(t) || isnan(h)) {
return;
}Print a Warning
When a read fails, print a clear message instead of a value. Future you will thank present you for the helpful note.
Serial.println("Failed to read DHT!");Retry, Do Not Crash
A single failure is normal, so do not stop the program. Simply retry on the next loop and the reading usually succeeds.
Keep the Last Good Value
For a steady display, store the last good reading and reuse it when a read fails. Your screen never shows an ugly blank.
Slow Down to Fix Failures
If failures pile up, you may be reading too fast or your wiring is loose. A longer delay and a firm connection often cure it.
Robust by Design
Handling errors gracefully is what separates a toy from a real device. Your sensor now survives the occasional hiccup calmly.
Quick Check
A DHT read fails. How should your sketch detect that in code?
Recap
You learned that failed reads return NaN, caught them with isnan, warned instead of crashing, and kept your device steady. 🎉
Frequently asked questions
Is the “Handle Failed Reads” lesson free?
Yes — the full text of “Handle Failed Reads” is free to read here on the web, and the Arduino & IoT Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Arduino & IoT Academy course, upgrade to CoddyKit PRO.
What will I learn in “Handle Failed Reads”?
Detect NaN and retry without crashing. You practise Arduino & IoT Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Arduino & IoT Academy?
No prior experience is required. Arduino & IoT Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Handle Failed Reads” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Arduino & IoT Academy lesson?
Yes. Every Arduino & IoT Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Wire the DHT11/DHT22
- Install the DHT Library
- Read Temperature & Humidity
- Handle Failed Reads