Lesson 1 of 4

Blink two LEDs, one of them backwards

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// Blink an LED on D1 and the blue LED on the module // R101 = 220 ohm: the LED current is (3.3 V - 2.0 V) / R101 const int LED_PIN = D1; // D1 is GPIO5, quiet at boot const int WAIT_MS = 500; void setup() { pinMode(LED_PIN, OUTPUT); pinMode(LED_BUILTIN, OUTPUT); // LED_BUILTIN is GPIO2 (D4), the blue LED on the ESP-12E } void loop() { digitalWrite(LED_PIN, HIGH); // HIGH lights the external LED digitalWrite(LED_BUILTIN, LOW); // LOW lights the blue LED: it is active low delay(WAIT_MS); digitalWrite(LED_PIN, LOW); digitalWrite(LED_BUILTIN, HIGH); delay(WAIT_MS); }

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Drive an LED on D1 and the module's blue LED on D4. The first lights on HIGH, the second on LOW.

Two LEDs, two logic senses
D-names versus GPIO numbers
Current through a 3.3 V pin

Pin	Connects to	What it does
`D1`	220 Ω resistor, then the red LED	output, HIGH = on
`D4`	blue LED on the ESP-12E (built in)	output, LOW = on
`GND`	LED cathode (short leg)	ground

Wire it in

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

LEDSupply 3.3 V
A 220 Ω resistor gives a red LED about 6 mA from a 3.3 V pin: (3.3 V - 2.0 V) / 220 Ω.
Part pin Board pin
anode (long leg), through 220 Ω D1Wire colour orange
cathode GNDWire colour black
Careful
Never connect an LED without a resistor: the pin is rated 12 mA. Blue and white LEDs need about 3 V and stay dim on 3.3 V.

All 12 parts on the NodeMCU (ESP8266) page

Connects to

What it does

D1

220 Ω resistor, then the red LED

output, HIGH = on

D4

blue LED on the ESP-12E (built in)

output, LOW = on

GND

LED cathode (short leg)

ground

Wire it in

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

LEDSupply 3.3 V

A 220 Ω resistor gives a red LED about 6 mA from a 3.3 V pin: (3.3 V - 2.0 V) / 220 Ω.

Part pin	Board pin
anode (long leg), through 220 Ω	D1Wire colour orange
cathode	GNDWire colour black

Careful

Never connect an LED without a resistor: the pin is rated 12 mA. Blue and white LEDs need about 3 V and stay dim on 3.3 V.

All 12 parts on the NodeMCU (ESP8266) page

Blink two LEDs, one of them backwards

Try it yourself

Serial monitor

Checks

Break it

Parameters

Wire it in

Blink two LEDs, one of them backwards

Try it yourself

Serial monitor

Checks

Break it

Parameters

Wire it in