You can download the datasheets for these chips here:<\/p>\n\n\n\n
BH1750FVI Datasheet<\/a> <\/p>\n\n\n\n For today\u2019s task I took the Nucleo with STM32F401RE<\/a> board. Since I am once again working with ready-made Chinese modules, the schematic is quite simple.<\/p>\n\n\n <\/p>\n\n\n\n Two of today\u2019s sensors communicate via the I\u00b2C interface. Additionally, one can assert interrupts, so I will assign a suitable pin for it. The third sensor outputs an analog value, so we need to prepare one of the analog inputs. The final pinout looks like this.<\/p>\n\n\n <\/p>\n\n\n\n I configure I\u00b2C at 400 kHz. The interrupt will need to react to the falling edge. I will discuss the ADC configuration later with the respective sensor.<\/p>\n\n\n\n <\/p>\n\n\n\n The first tested sensor is the low-power BH1750 from ROSH Semicondutor<\/em>( The sensor can operate in several modes:<\/p>\n\n\n\n The manufacturer recommends using the high-resolution mode with a 1 lux resolution. Allegedly it handles interference well. I also like it because the value in the measurement registers will not need to be converted. In continuous mode the measurement is performed cyclically at 120 ms or 16 ms intervals depending on the chosen mode. In manual mode, the conversion is triggered only once. You must then wait until the ADC finishes (120 ms for high-res and 16 ms for low-res) before you can read the measurement value. Unlike continuous operation, in manual mode the sensor automatically enters Power Down after the conversion where the current consumption is negligible (typ. 0.01 \u00b5A) compared to what is required for conversion (typ. 120 \u00b5A). You don\u2019t have to wake the sensor manually. Just request a conversion.<\/p>\n\n\n\n The register table is basically not a register table. You communicate with the sensor using a set of commands without writing anything directly to its memory. Let\u2019s move on to the code.<\/p>\n\n\n\n In the first step, the sensor should be initialized. In addition to passing a pointer to the I\u00b2C interface used, I reset the sensor and set its default measurement time<\/em> value.<\/p>\n\n\n\n The following functions are used to reset the sensor and control the Power Down state<\/p>\n\n\n\n If you need to change the sensor\u2019s sensitivity, use<\/p>\n\n\n\n Set the mode in which the sensor is to operate with<\/p>\n\n\n\n using an enum variable with predefined commands. This reduces the risk of mistakes.<\/p>\n\n\n\n If you will be using manual mode, you will need a function that triggers the conversion. In fact, it just sends the command to set the conversion mode because that\u2019s what the sensor requires, but who would remember throughout the project which mode is used \ud83d\ude09<\/p>\n\n\n\n And the most important one: the function to read the value measured by the sensor. Its usage should be straightforward.<\/p>\n\n\n\n What does a read from the sensor look like? It\u2019s enough to receive data directly from its address. Its address is at the same time the register from which the result is read. There\u2019s no great philosophy here, hence the reading and value conversion are instantaneous. In high resolution 2<\/em> mode with 0.5 lux precision, it takes 0.28 ms for a 100 kHz I\u00b2C clock and 80 \u00b5s for 400 kHz.<\/p>\n\n\n 100 kHz:<\/p>\n\n\n 400 kHz:<\/p>\n\n\n\n Remember that if you want to use manual conversion, you must wait the appropriate time between requesting the measurement and reading it. Of course, the data can be read using DMA. Try to do it yourself \ud83d\ude42<\/p>\n\n\n\n <\/p>\n\n\n\n The next sensor today is the MAX44009 from Maxim<\/em> Integrated<\/em> ( Another difference is the INT<\/em> pin, i.e. the ability for the chip to assert an interrupt to the microcontroller. The interrupt can be asserted after exceeding one of the configurable light intensity thresholds \u2014 upper or lower. At the same time, a minimum time the threshold must be exceeded is defined to decide whether to assert the interrupt. Of course, the thresholds can be set as a window. Importantly, the interrupt will be asserted even if it is operating in manual mode.<\/p>\n\n\n\n Because the MAX44009 is a bit more feature-rich, the library is more extensive. Initialization only assigns the I\u00b2C pointer:<\/p>\n\n\n\n Next are the sensor configuration functions. You can write the appropriate value to the register in one go, or use several convenient self-documenting functions that change only one function.<\/p>\n\n\n\n Note the last function, which takes an enum as an argument:<\/p>\n\n\n\n The most important part is of course reading the ambient light value. As I mentioned earlier, it can be done in two ways and I have included both.<\/p>\n\n\n\n Here\u2019s a little curiosity. The datasheet says: \u201cIf user wants to read both the Lux High-Byte register 0x03 and Lux Low-Byte register 0x04, then the master should not send a STOP command between the reads of the two registers. Instead a Repeated START command should be used.\u201d<\/em> What does this mean? The chip will increment the register address to be read on its own provided that after reading the first one, the master repeats a START sequence on the I\u00b2C bus. Unfortunately, when using the HAL<\/em> function HAL_I2C_Mem_Read<\/em> the microcontroller does not issue a START between consecutive bytes read. As a result, the sensor provides the value of register 0x03 twice instead of 0x04 in the second byte.<\/p>\n\n\n <\/p>\n\n\n\n The simplest solution will be to simply call HAL_I2C_Mem_Read<\/em> twice. Unfortunately, this costs a second addressing of the sensor and specifying the register from which to read.<\/p>\n\n\n <\/p>\n\n\n\n If it turns out you need to shorten this time for some reason, a solution could be to use HAL_I2C_Master_Sequential_Receive_IT<\/em>. Try to improve the readout with it \ud83d\ude42<\/p>\n\n\n\n Finally, there are functions useful for interrupts.<\/p>\n\n\n\n The interrupt flag in the sensor is cleared automatically after reading the status register or disabling the interrupt. The boundary values that affect interrupt assertion are provided to and stored by the sensor in floating-point form with reduced resolution (4-bit exponent and 4-bit mantissa). Remember this limitation<\/strong>. The time requirement to assert the interrupt, passed in the argument, is in tens of milliseconds (value * 10 ms). So for a one-second setting, you should pass the value 100.<\/p>\n\n\n\n A few more numbers and plots.<\/p>\n\n\n\n 100k low resolution:<\/p>\n\n\n <\/p>\n\n\n\n 400k low resolution:<\/p>\n\n\n <\/p>\n\n\n\n 100k high resolution:<\/p>\n\n\n <\/p>\n\n\n 400k high resolution:
MAX44009 Datasheet<\/a>
TEMT6000 Datasheet<\/a><\/p>\n\n\n\nSchematic and Cube configuration<\/h2>\n\n\n
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BH1750FVI Datasheet<\/a>
). You can talk to it over the I\u00b2C interface with a maximum clock frequency of 400 kHz. It has a built-in ADC that converts the measured light intensity into a digital value. Its measurement range is 1 \u2013 65535 lux. The sensor allows calibration of measurement sensitivity. Thanks to this it can detect as low as 0.11 lux. This setting can also be adjusted to the covering material, e.g. glass. You should know the value of the light transmission through that material. See the datasheet for details.<\/p>\n\n\n\n\n
BH1750_STATUS BH1750_Init(I2C_HandleTypeDef *hi2c);<\/pre>\n\n\n\n
BH1750_STATUS BH1750_Reset(void);\nBH1750_STATUS BH1750_PowerState(uint8_t PowerOn);<\/pre>\n\n\n\n
BH1750_STATUS BH1750_SetMtreg(uint8_t Mtreg);<\/pre>\n\n\n\n
BH1750_STATUS BH1750_SetMode(bh1750_mode Mode);\n<\/pre>\n\n\n\n
typedef enum\n{\n\tCONTINUOUS_HIGH_RES_MODE = 0x10,\n\tCONTINUOUS_HIGH_RES_MODE_2 = 0x11,\n\tCONTINUOUS_LOW_RES_MODE = 0x13,\n\tONETIME_HIGH_RES_MODE = 0x20,\n\tONETIME_HIGH_RES_MODE_2 = 0x21,\n\tONETIME_LOW_RES_MODE = 0x23\n}bh1750_mode;\n<\/pre>\n\n\n\nBH1750_STATUS BH1750_TriggerManualConversion(void);<\/pre>\n\n\n\n
BH1750_STATUS BH1750_ReadLight(float *Result);\n<\/pre>\n\n\n\n
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MAX44009 Datasheet<\/a>
). Like the BH1750, it has a built-in ADC and an I\u00b2C communication interface. It differs, among other things, in the way the result is encoded. It is stored in floating-point form with a 4-bit exponent and an 8-bit mantissa. I wrote about floating-point numbers here<\/a>. The way the measurement value is stored allows you to read the result with different precision. You can read two registers and get a high-resolution result, or you can skip the second register, which contains the lower bits of the mantissa, and enjoy a faster result but with lower resolution.<\/p>\n\n\n\nMAX44009_STATUS MAX44009_Init(I2C_HandleTypeDef *hi2c);<\/pre>\n\n\n\n
MAX44009_STATUS MAX44009_ReadConfigurationRegister(uint8_t *Config);\nMAX44009_STATUS MAX44009_WriteConfigurationRegister(uint8_t Config);\n\nMAX44009_STATUS MAX44009_ContinuousMode(uint8_t Enable);\nMAX44009_STATUS MAX44009_ManualConfiguration(uint8_t Enable);\nMAX44009_STATUS MAX44009_CurrentDivisionRatio(uint8_t Enable);\nMAX44009_STATUS MAX44009_IntegrationTime(max44009_timer Timer);<\/pre>\n\n\n\n
typedef enum\n{\n\tINTEGRATION_TIME_6_25_MS = 0x07, \/\/ Manual mode only\n\tINTEGRATION_TIME_12_5_MS = 0x06, \/\/ Manual mode only\n\tINTEGRATION_TIME_25_MS = 0x05, \/\/ Manual mode only\n\tINTEGRATION_TIME_50_MS = 0x04, \/\/ Manual mode only\n\tINTEGRATION_TIME_100_MS = 0x03, \/\/ This is a preferred mode for high-brightness applications\n\tINTEGRATION_TIME_200_MS = 0x02,\n\tINTEGRATION_TIME_400_MS = 0x01,\n\tINTEGRATION_TIME_800_MS = 0x00 \/\/ This is a preferred mode for boosting low-light sensitivity\n} max44009_timer;<\/pre>\n\n\n\nMAX44009_STATUS MAX44009_ReadLightLowResolution(float *Result);\nMAX44009_STATUS MAX44009_ReadLightHighResolution(float *Result);<\/pre>\n\n\n\n
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<\/a><\/figure>\n<\/div>\n\n\nMAX44009_STATUS MAX44009_ReadInterruptStatus(uint8_t *Status);\nMAX44009_STATUS MAX44009_WriteInterruptEnable(uint8_t Enable);\n\nMAX44009_STATUS MAX44009_SetUpperThreshold(float Threshold);\nMAX44009_STATUS MAX44009_SetLowerThreshold(float Threshold);\nMAX44009_STATUS MAX44009_SetThresholdTimer(uint8_t Timer);<\/pre>\n\n\n\n
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