sds011-esp-raw

ESP-IDF component which provides a low level interface to the SDS011 particulate matter sensor.

Fundamentals

This library works by using three queues:

1. Outgoing packets to the sensor (commands)
2. Command response packets from the sensor
3. Sensor measurement packets from the sensor

The reason for splitting the packets from the sensor into two queues is to separate explicitly requested responses from automatically sent sensor measurements when the sensor is in active mode. In this case the sent measurements might be the first incoming packet after sending a command, which makes assigning the response packet to the request packet harder.

Usage

Note: The library can only mange a single UART port with a sensor.

Initialization

To initialize the library, call

sds011_begin(UART_NUM, TX_IO_NUM, RX_IO_NUM);

where UART_NUM is the UART port to use, either UART_NUM_1 or UART_NUM_2. UART_NUM_0 is also available, but conventionally used for logging output. TX_IO_NUM is number of the GPIO port connected to the RX port of the SDS011 and RX_IO_NUM the one connected to its TX port.

This function must be called before using any of the functions below.

If the provided parameters are invalid, calling this function will cause an abort.

Sending packets

Packets can be sent calling

sds011_send_cmd_to_queue(PACKET_PTR, WAIT_TICKS);

where PACKET_PTR is a pointer to a struct of the type sds011_tx_packet and WAIT_TICKS is the number of ticks to wait for an available slot in the queue in case it is currently full. The packet struct will be copied by the function.

Returns SDS011_OK when the packet was successfully enqueued, SD011_TIMEOUT otherwise.

An example packet struct can be initialized like this:

struct sds011_tx_packet packet = (struct sds011_tx_packet){
        .head = SDS011_PACKET_HEAD,
        .command = SDS011_CMD_TX,
        .sub_command = SDS011_TX_CMD_SLEEP_MODE,
        .payload_sleep_mode = {.method = SDS011_METHOD_SET,
                               .mode = SDS011_SLEEP_MODE_ENABLED},
        .device_id = SDS011_DEVICE_ID_ALL,
        .tail = SDS011_PACKET_TAIL};

All of the values used above are defined in sds011_consts.h.

When sending a packet, the head, command and tail fields always contain the same values as shown above. device_id is the ID of the sensor to communicate with, the value of SDS011_DEVICE_ID_ALL, which is 0xFFFF, acts like a broadcast address.

sub_command is one of the SDS011_TX_CMD_* values and declares which payload the packet contains. In this case the sub command specifies that the payload is a sleep mode command.

The payload_* fields of the tx_packet are an anonymous union, which means only one of them must be set. In the example above payload_sleep_mode is used, since the sub_command field specified the the payload as sleep mode command.

The checksum field is automatically populated by the library.

More information about the possible payload structs can be found in the corresponding header file, sds011_structs.h.

Receiving command response packets

Note: The response to data query commands is a regular sensor data packet, which is sent to the data queue.

Command response packets can be received calling

sds011_recv_cmd_from_queue(DEST_PACKET_PTR, TICKS_TO_WAIT);

where DEST_PACKET_PTR is a pointer to a struct sds011_rx_packet, to which the received data is written to and TICKS_TO_WAIT is the amount of ticks to wait for an available packet in case the queue is empty.

Returns SDS011_OK when a packet was successfully received, SD011_TIMEOUT otherwise.

More information about RX packet structure can also be found in the header file sds011_structs.h.

Receiving data packets

Command response packets can be received calling

sds011_recv_data_from_queue(DEST_PACKET_PTR, TICKS_TO_WAIT);

The usage is the same as receiving command response packets. It can be assumed any packet received has the payload field payload_query_data.

Deinitialization

The resources used by the library can be released using

sds011_end();

The send and receive functions should not be used afterwards if the library does not get initialized again.

Examples

See periodic_read.c in the examples directory. It shows how to use this library to send sleep commands and to receive values.

Resources

This library has been developed using the Laser Dust Sensor Control Protocol V1.3 documentation from Nova Fitness.

Some findings about the sensor gathered during development and testing can be found in the docs directory.