light-meter-bh1750.md

BH1750 light meter

General info

BH1750 light meter looks like this:

Library to handle it: https://github.com/claws/BH1750

Connecting to Arduino

BH1750 pin	Arduino pin	Details
VCC	VCC
GND	GND
SCL	A5 (analog)	Serial clock (I2C)
SDA	A4 (analog)	Serial data (I2C)
ADDR	GND	If ADDR is LOW, I2C address is 0x23. If it's HIGH, address will be 0x5C (TODO: verify that). This way it is possible to connect two light meters to one Arduino.

Note on I2C

BH1850 uses I2C addressing. According to this article:

The Two-Wire interface is extremely useful for connecting multiple devices, as they can all share the same two pins (plus a ground return). This is because the devices are "addressable". Each device needs to have a unique address in the range 8 to 119. Address 0 is reserved as a "broadcast" address, addresses 1 to 7 are reserved for other purposes, and addresses 120 to 127 are reserved for future use.

On most Arduino boards, pin 4 (analog) maps to SDA (serial data), and pin 5 to SCL (serial clock).

Code sample

This will print the light level every ~500 msec (actually it's longer than that, because the measurement of light level itself takes time - according to the documentation, around ~120 msec).

Light meter will be in the low power mode in betweeen measurements.

#include <Wire.h>
#include "BH1750.h"

BH1750 light_meter;

uint16_t read_light_level() {
  // In this mode, light meter will automatically
  // move to power down mode after measurement.
  // No need to do this manually.
  // For other possible modes, see BH1750.h.
  light_meter.configure(BH1750_ONE_TIME_LOW_RES_MODE);
  return light_meter.readLightLevel();
}

void setup() {
  Serial.begin(9600);

  // Initially, light meter will be in power down mode.
  // We will power it up before each measurement in order
  // to save power.
  light_meter.begin(BH1750_POWER_DOWN);
}

void loop() {
  Serial.print("Alive!\n");

  uint16_t light_level = read_light_level();
  Serial.print("Light level: ");
  Serial.print(light_level);
  Serial.print("\n");

  delay(500);
}