Lesson 11 of 16

Keep it cool

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const int SENSOR = A0; const int FAN = 6; // the fan runs through the TIP120, like the motor const float LIMIT = 30; // turn the fan on above this void setup() { Serial.begin(9600); pinMode(FAN, OUTPUT); } void loop() { int raw = analogRead(SENSOR); float volts = raw * 5.0 / 1023.0; // 0-1023 back to 0-5 V float tempC = (volts - 0.5) * 100.0; // TMP36: 0.5 V at 0 °C, plus 10 mV per °C Serial.println(tempC); if (tempC > LIMIT) { analogWrite(FAN, 255); } else { analogWrite(FAN, 0); } delay(200); }

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

A TMP36 turns temperature into a voltage. The sketch converts it to degrees and switches on a fan through a transistor when it gets too warm.

From ADC reading to degrees in two lines
Heat the sensor and the fan kicks in
On-off or speed with the heat

Pin	Connects to	What it does
`5V`	The TMP36's +VS leg	Powers the sensor, and the fan.
`A0`	The TMP36's middle leg (VOUT)	Reads the temperature as a voltage.
`GND1`	The TMP36's GND leg	Ground.
`D6`	1 kΩ resistor, then the transistor's base	Switches the fan.

Wire it in

Sensors and actuators this board drives, with the real connections.

PotentiometerSupply 5 V
Ends to GND and 5V, the middle leg (wiper) to A0. analogRead(A0) then goes from 0 to 1023 as you turn it.
Part pin Board pin
1 GNDWire colour black
2 A0Wire colour green
3 5VWire colour red
Light sensor (LDR)Supply 5 V
From 5V to A0, with a 10 kΩ resistor from A0 to GND. More light, lower resistance, higher reading.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour green
TMP36 temperature sensorSupply 5 V
Flat face toward you: left leg 5V, middle leg to A0, right leg GND. Degrees C = (volts − 0.5) × 100.
Part pin Board pin
VS 5VWire colour red
VOUT A0Wire colour green
GND GNDWire colour black
TIP120 Darlington transistorSupply 5 V
Base through a 1 kΩ resistor to a PWM pin, emitter to GND, the load from 5 V (or its own supply) to the collector.
Part pin Board pin
B D6Wire colour orange
E GNDWire colour black
Careful
A motor or fan needs a 1N4007 diode across it, band toward the + supply, or switching it off sends a voltage spike into the transistor.
Capacitive soil moisture sensorSupply 5 V
AOUT to A0, VCC to 5V, GND to GND. The reading falls as the soil gets wetter.
Part pin Board pin
AOUT A0Wire colour yellow
VCC 5VWire colour red
GND GNDWire colour black
FSR 402 force sensorSupply 5 V
One leg to 5V, the other to A0, with a 10 kΩ pull-down from A0 to GND. Press harder, read higher.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour green

All 16 parts on the Arduino Uno R3 page

Connects to

What it does

5V

The TMP36's +VS leg

Powers the sensor, and the fan.

A0

The TMP36's middle leg (VOUT)

Reads the temperature as a voltage.

GND1

The TMP36's GND leg

Ground.

D6

1 kΩ resistor, then the transistor's base

Switches the fan.

Wire it in

Sensors and actuators this board drives, with the real connections.

PotentiometerSupply 5 V

Ends to GND and 5V, the middle leg (wiper) to A0. analogRead(A0) then goes from 0 to 1023 as you turn it.

Part pin	Board pin
1	GNDWire colour black
2	A0Wire colour green
3	5VWire colour red

Light sensor (LDR)Supply 5 V

From 5V to A0, with a 10 kΩ resistor from A0 to GND. More light, lower resistance, higher reading.

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour green

TMP36 temperature sensorSupply 5 V

Flat face toward you: left leg 5V, middle leg to A0, right leg GND. Degrees C = (volts − 0.5) × 100.

Part pin	Board pin
VS	5VWire colour red
VOUT	A0Wire colour green
GND	GNDWire colour black

TIP120 Darlington transistorSupply 5 V

Base through a 1 kΩ resistor to a PWM pin, emitter to GND, the load from 5 V (or its own supply) to the collector.

Part pin	Board pin
B	D6Wire colour orange
E	GNDWire colour black

Careful

A motor or fan needs a 1N4007 diode across it, band toward the + supply, or switching it off sends a voltage spike into the transistor.

Capacitive soil moisture sensorSupply 5 V

AOUT to A0, VCC to 5V, GND to GND. The reading falls as the soil gets wetter.

Part pin	Board pin
AOUT	A0Wire colour yellow
VCC	5VWire colour red
GND	GNDWire colour black

FSR 402 force sensorSupply 5 V

One leg to 5V, the other to A0, with a 10 kΩ pull-down from A0 to GND. Press harder, read higher.

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour green

All 16 parts on the Arduino Uno R3 page

Keep it cool

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Keep it cool

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in