Level 3Unit B · Session 12
12

Unit B · What your device can sense

One page, everything on it

What we are making: nothing new. Today three things you have already built go onto one board, and one page shows all of them.

No new components

The temperature sensor from session 7, the light sensor from session 8, and the servo from session 10. Every one of them worked on its own. The only question today is whether they still work together — and the answer, the first time, is usually not quite.

ESP32power from the railsGPIO 4GPIO 34GPIO 13DHT11temperatureoutLight sensorbrightnessAOServothe moving partOrangeOnly the signal wires are drawn. Every module also needs power and ground — take those from the breadboard rails,not by stacking three wires onto one ESP32 pin.
Everything at once. This is the machine your page will show.

Do it, in this order

  1. Wire the power rails first: 3.3V to one rail, GND to the other, VIN to a spare row.
  2. Add one module. Test it. Only then add the next.
  3. Build the page up the same way — one reading at a time, refreshing between each.
  4. When all three work, hand your phone to another team and have them try it.
💡 Tip
Add one thing at a time, always. If you wire all three and it does not work, you have three suspects and no evidence. If you add them one at a time, the thing that broke it is the thing you just added. This sounds obvious and almost nobody does it.

What usually goes wrong

What you seeWhyWhat to do
Everything worked separately, nothing works nowPower, almost always.Three modules on one 3.3V pin is too much. Use the breadboard rails.
The board resets whenever the servo movesServo on the wrong supply.VIN, not 3.3V. Same as session 10.
One reading is always the sameThat module's wire came loose while wiring another.Check the wires you did not just add.
The page takes several secondsThe DHT11 is slow and you are reading it every time.Read it once every few seconds and remember the value.

Hand in

  • One board, three components, one page showing all of them.
  • Your light threshold, and the sentence explaining it.
  • One thing that broke when you combined them, and what it turned out to be.

What you learned

  • Things that work separately do not automatically work together.
  • Power is the commonest reason for that, by a long way.
  • Adding one at a time turns a mystery into a five-minute fix.
Challenge optional — only if you finish early
  • Add a fourth module to the three already working. Which one broke, and why?
11. Switching something bigger