ESP32 Forum

I am using an ESP32-S3-WROOM-1 chip as a BLE 5 GATT client (this is what we call the “brain”) and an ESP32-C3-WROOM-02 as the BLE 5 GATT server (this is a “sensor”). Both devices are headless, there are no buttons or screens.

To conserve battery life on the sensor, the sensor will go into a deep sleep state and wake up periodically to transmit information to the brain. I had a lot of trouble understanding the best way to implement the BLE functionality, but I was able to piece together a solution based on the ESP32 code examples. Although it seems to work, it needs to be improved. Let me share with you, my concerns. I greatly appreciate any help you can offer.

To aid in my explanation, I have provided you a link to a folder on my OneDrive. The password is: 3SPHelp$

https://1drv.ms/u/s!AqYgHKn2LJ7yhbYRWzB4R_Arxl-HAg?e=0X7LdK

• ble_client.c – BLE code used on the brain. Some contents of the file has been changed/deleted.
• ble_server.c – BLE code used on the sensor. Some contents of the file has been changed/deleted.
• ble5-gatt-slow-esp-idf.mp4 – Video to demonstrate the poor performance connecting via BLE.

Q1. It takes a very long time to establish a connection between the GATT server and client.

When the sensor wakes up, the process of connecting, reading data, and disconnecting will take about 27 seconds. This is a very long time and I wonder how it can be improved. If you watch the video I have provided you, it will be clear what I am referring to.

In the video:

• The brain is shown on the left and the sensor is on the right. Ignore the information that is displayed on the screen when the video begins.
• At 0:03 the sensor begins wakes up and begins to advertise. The brain starts the connection process almost immediately - this is fantastic.
• At 0:07 the connection is established. It took almost 4 seconds. Now the devices show the “ESP_LE_AUTH_REQ_SC_BOND” message.
• At 0:20 the devices have bonded. This took 13 seconds. It is too long in my opinion.
• The last several seconds of the video, data is transferred.

How can I improve the length of time needed for the entire process I illustrated above. As I mentioned earlier, I struggled to understand best practices implementing BLE using IDF. Do I even need to “bond” the devices? Can I skip any of the steps?


Q2. Am I using BLE 5 long range (coded)?

At the time I developed this, there were very few examples with BLE 5 coded. In this design, I want to use BLE 5 coded at the longest range possible. I do not need to send a lot of data and I do not need to send data at a fast speed. Distance is very important to me.

I was unable to confirm my code establishes a BLE 5 coded connection. As an example, I couldn’t figure out how to have the sensor send the BLE advertisement using BLE 5 coded. If the advertisement is not received by the brain, then it will not know to establish a connection.

Are you able to either review my code files to see if I have correctly set the BLE protocols and advertising correctly? Or, if you can provide a more complete BLE 5 coded example with GATT I am happy to do this myself.

Answer of Q1:

The process of connecting, reading data, and disconnecting takes approximately 27 seconds, which is likely due to an improper interval setting. To further optimize it, you can set a smaller interval using the following configuration:

```
const esp_ble_gap_conn_params_t phy_coded_conn_params = {
.scan_interval = 0x40,
.scan_window = 0x40,
.interval_min = 10,
.interval_max = 10,
.latency = 0,
.supervision_timeout = 600,
.min_ce_len = 0,
.max_ce_len = 0,
};
```



Answer of Q2:

Whether to use BLE 5 coded phy is determined by the server-side. You can use "esp_ble_gap_read_phy" to check if it is being used. If you want to change the phy, you can reconfigure it using "esp_ble_gap_set_preferred_phy".

BTW:
I haven't seen the file provided by OneDrive. It might have been deleted. If you still have any questions, you can upload the materials in the form of attachments.

Can you please share the example how to use "esp_ble_gap_set_preferred_phy" ?
In my case when I use "esp_ble_gap_set_preferred_phy" I got below error:
BT_BTM: BTM_BleSetPreferPhy, invalid parameters

How do you use the `esp_ble_gap_set_preferred_phy` API?



```
//when connected
esp_bd_addr_t remote_device_address = {0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC};//peer bluetooth addr
esp_ble_gap_all_phys_t all_phys = 0;
esp_ble_gap_phy_mask_t tx_phy = ESP_BLE_GAP_PHY_2M_PREF_MASK; // 2Mbps data rate
esp_ble_gap_phy_mask_t rx_phy = ESP_BLE_GAP_PHY_2M_PREF_MASK;
esp_ble_gap_prefer_phy_options_t phy_options = ESP_BLE_GAP_PHY_OPTIONS_NO_PREF;

esp_err_t result = esp_ble_gap_set_preferred_phy(remote_device_address,
all_phys,tx_phy,rx_phyphy_options)
```

Each parameter's specific description can be found in the BLUETOOTH CORE SPECIFICATION Version 5.4 | Vol 4, Part E page 2440.

I want to use BLE 5 coded at the longest range possible

Then you probably want to use ESP_zhanghaipeng's code with and/or And you may want to use "extended advertisements", allowing you to set esp_ble_gap_ext_adv_params_t::primary_phy to ESP_BLE_GAP_PRI_PHY_CODED.

Or, you skip the complexity and overhead of Bluetooth alltogether and just use ESP-NOW.