Lesson 2 of 4

The FLASH button and a light sensor

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// Press FLASH (D3) to read the light level on A0 const int BUTTON = D3; // FLASH button: GPIO0, LOW while pressed const int LIGHT = A0; // LDR divider on the only analog pin bool wasPressed = false; void setup() { Serial.begin(115200); pinMode(BUTTON, INPUT); // R1 on the board is the pull-up pinMode(LED_BUILTIN, OUTPUT); digitalWrite(LED_BUILTIN, HIGH); // HIGH switches the blue LED off Serial.println("ready: press FLASH"); } void loop() { bool pressed = digitalRead(BUTTON) == LOW; digitalWrite(LED_BUILTIN, pressed ? LOW : HIGH); if (pressed && !wasPressed) { int raw = analogRead(LIGHT); float volts = raw * 3.2 / 1023.0; // the board's divider makes 3.2 V read as 1023 Serial.print("A0 raw="); Serial.print(raw); Serial.print(" volts="); Serial.println(volts, 2); } wasPressed = pressed; delay(20); // a short pause also rides over contact bounce }

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

Nothing printed yet. Press Run.

Use the FLASH button on D3 as an input and take a light reading on A0 each time it is pressed.

An on-board button as input
A light sensor on the only ADC pin
One reading per press, not per loop

Pin	Connects to	What it does
`D3`	FLASH button on the board	input, 12 kΩ pull-up on the board
`D4`	blue LED on the ESP-12E	output, LOW = on
`A0`	LDR and 10 kΩ divider	analog input, 0-3.2 V
`3V3`	top of the LDR	3.3 V supply
`GND`	bottom of the 10 kΩ resistor	ground

Wire it in

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

PotentiometerSupply 3.3 V
Ends to 3V3 and GND, wiper to A0. The top 0.1 V of travel reads 1023 because A0's full scale is 3.2 V.
Part pin Board pin
end 1 3V3Wire colour red
wiper A0Wire colour yellow
end 2 GNDWire colour black
Light sensor (LDR)Supply 3.3 V
LDR from 3V3 to A0 and 10 kΩ from A0 to GND: more light gives a higher reading.
Part pin Board pin
LDR leg 1 3V3Wire colour red
LDR leg 2 + 10 kΩ to GND A0Wire colour yellow
TMP36 temperature sensorSupply 3.3 V
Runs from 3.3 V (2.7-5.5 V). 0.5 V means 0 °C and each 10 mV is 1 °C: °C = (raw x 3.2 / 1023 - 0.5) x 100.
Part pin Board pin
+Vs 3V3Wire colour red
Vout A0Wire colour yellow
GND GNDWire colour black
Capacitive soil moisture sensorSupply 3.3 V
AO to A0, powered from 3V3 so the output never exceeds the 3.2 V range. Power it only while measuring to slow corrosion.
Part pin Board pin
VCC 3V3Wire colour red
GND GNDWire colour black
AO A0Wire colour yellow

All 12 parts on the NodeMCU (ESP8266) page

Connects to

What it does

D3

FLASH button on the board

input, 12 kΩ pull-up on the board

D4

blue LED on the ESP-12E

output, LOW = on

A0

LDR and 10 kΩ divider

analog input, 0-3.2 V

3V3

top of the LDR

3.3 V supply

GND

bottom of the 10 kΩ resistor

ground

Wire it in

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

PotentiometerSupply 3.3 V

Ends to 3V3 and GND, wiper to A0. The top 0.1 V of travel reads 1023 because A0's full scale is 3.2 V.

Part pin	Board pin
end 1	3V3Wire colour red
wiper	A0Wire colour yellow
end 2	GNDWire colour black

Light sensor (LDR)Supply 3.3 V

LDR from 3V3 to A0 and 10 kΩ from A0 to GND: more light gives a higher reading.

Part pin	Board pin
LDR leg 1	3V3Wire colour red
LDR leg 2 + 10 kΩ to GND	A0Wire colour yellow

TMP36 temperature sensorSupply 3.3 V

Runs from 3.3 V (2.7-5.5 V). 0.5 V means 0 °C and each 10 mV is 1 °C: °C = (raw x 3.2 / 1023 - 0.5) x 100.

Part pin	Board pin
+Vs	3V3Wire colour red
Vout	A0Wire colour yellow
GND	GNDWire colour black

Capacitive soil moisture sensorSupply 3.3 V

AO to A0, powered from 3V3 so the output never exceeds the 3.2 V range. Power it only while measuring to slow corrosion.

Part pin	Board pin
VCC	3V3Wire colour red
GND	GNDWire colour black
AO	A0Wire colour yellow

All 12 parts on the NodeMCU (ESP8266) page

The FLASH button and a light sensor

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

The FLASH button and a light sensor

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in