Uses service data instead of manufacturer specific data for advertising sensor values

code/parasite/src/main.cpp

@@ -13,17 +13,26 @@ constexpr int kSensAnalogPin = 4;  // AIN2
 constexpr int kDischargeEnablePin = 16;
 constexpr double kPWMFrequency = 500000;
 
-char manufacturer_data[] = {
-    0x01,
-    0x02,
-    0x03,
-};
-
 constexpr int kManufacturerDataLen = 3;
 
+// We can have at most 31 bytes here.
+uint8_t advertisement_data[] = {
+    9, // Length of name.
+    BLE_GAP_AD_TYPE_COMPLETE_LOCAL_NAME,
+    'P', 'a', 'r', 'a', 's', 'i', 't', 'e',
+    7, // Length of the service data.
+    BLE_GAP_AD_TYPE_SERVICE_DATA,
+    0x1a, 0x18,  // Environment sensor service UUID.
+    0x00, 0x00,  // Raw soil humidity.
+    0x00, 0x00,  // Percentage soil humidity.
+};
+constexpr size_t kRawSoilMoistureOffset = 14;
+constexpr size_t kPercentSoilMoistureOffset = kRawSoilMoistureOffset + 2;
+constexpr size_t kTemperatureOfsset = kRawSoilMoistureOffset + 4;
+
 ble_gap_addr_t kGAPAddr{
     1,
-    BLE_GAP_ADDR_TYPE_RANDOM_STATIC,
+    BLE_GAP_ADDR_TYPE_PUBLIC,
     // This is the "reverse" order in comparison that the colon-separated
     // human-readable MAC addresses.
     {0x01, 0x02, 0x03, 0x04, 0x05, 0x06},
@@ -36,13 +45,16 @@ void setupAdvertising() {
 }
 
 void updateAdvertisingData(int moisture_level) {
-  manufacturer_data[2] = moisture_level & 0xff;
+  uint16_t packed_raw_moisture = moisture_level;
-  manufacturer_data[1] = 0xff;
+  advertisement_data[kRawSoilMoistureOffset] = packed_raw_moisture >> 1;
+  advertisement_data[kRawSoilMoistureOffset + 1] = packed_raw_moisture & 0xff;
+  // manufacturer_data[1] = 0xff;
   Bluefruit.Advertising.stop();
   Bluefruit.Advertising.clearData();
-  Bluefruit.Advertising.addName();
+  // Bluefruit.Advertising.addName();
-  Bluefruit.Advertising.addManufacturerData(manufacturer_data,
+  // Bluefruit.Advertising.addManufacturerData(manufacturer_data,
-                                            kManufacturerDataLen);
+  //                                           kManufacturerDataLen);
+  Bluefruit.Advertising.setData(advertisement_data, sizeof(advertisement_data));
   Bluefruit.Advertising.setInterval(32, 244);  // in unit of 0.625 ms
   Bluefruit.Advertising.setFastTimeout(30);    // number of seconds in fast mode
   Bluefruit.Advertising.start(0);  // 0 = Don't stop advertising after n seconds
@@ -58,6 +70,12 @@ void setup() {
   analogReference(AR_VDD4);
 
   setupAdvertising();
+
+  Serial.println("Will advertise with MAC:");
+  for (const auto byte : kGAPAddr.addr) {
+    Serial.printf("0x%02x ", byte);
+  }
+  Serial.println();
 }
 
 void loop() {

resources.md

@@ -151,6 +151,11 @@ I'm getting ~680 when in the air; ~65 while holding the sensor. The default reso
   * [main_loop](https://github.com/atc1441/ATC_MiThermometer/blob/916cef7db24977ec187e68ab6e718b7b7a4988e6/ATC_Thermometer/app.c#L76)
   * [advertisement_data](https://github.com/atc1441/ATC_MiThermometer/blob/master/ATC_Thermometer/ble.c#L39) definition
   * [set_adv_data](https://github.com/atc1441/ATC_MiThermometer/blob/master/ATC_Thermometer/ble.c#L178) - where the temp, humidity and batt levels are encoded into the advertisement data
+  * They don't use manufacturer data. They use a custom UUID service (0x181a).
+  * Using the manufacturer data requires a SIG membership for getting the manufacturer ID (first two bytes in the manufacturer data)
+  * Using the service data also requires applying for a 16-bit (2 byte) ID from SIG ([link](https://www.bluetooth.com/specifications/assigned-numbers/))
+  * Aha! I think we can use the 0x181a service UUID (the same one the alternative xiaomi firmware uses). This service is reserved for "Environmental Sensors". Check out the offical assigned numbers list [here](https://btprodspecificationrefs.blob.core.windows.net/assigned-values/16-bit%20UUID%20Numbers%20Document.pdf).
+    * We can use the SERVICE_DATA (int 16) in the BLE advertisement packet to pack service data for the UUID 0x181a.
 * How the xiaomi BLE temp sensor works in ESPHome: [link](https://github.com/esphome/esphome/blob/5c86f332b269fd3e4bffcbdf3359a021419effdd/esphome/components/xiaomi_lywsd03mmc/xiaomi_lywsd03mmc.cpp)
 * [How advertisement works YouTube video](https://www.youtube.com/watch?v=CJcLabp42b4) by nordic
   * In your case:
@@ -176,8 +181,8 @@ I'm getting ~680 when in the air; ~65 while holding the sensor. The default reso
 * Can we update the manufaturer advertising data dynamically?
   * [Hint on devzone.nordicsemi.com](https://devzone.nordicsemi.com/f/nordic-q-a/11217/adc-values-in-advertising-data-dynamically-changing)
 * What MAC address to use?
-  * Public
+  * Public - might have some security implications, since BLE can be used for tracking
-  * Random
+  * Random - safer, since its random, but it "breaks" our MAC-addr based Hub config
 
 ## Packing values into the advertising packet
 ### Soil humidity