Make BLE TX power configurable for nRF52 variants (#9232)

* Make BLE TX power configurable for nRF52 variants

* Include BLE TX power setting in T114 variant.h as tested

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/platform/nrf52/NRF52Bluetooth.cpp

@@ -240,6 +240,14 @@ int NRF52Bluetooth::getRssi()
 {
     return 0; // FIXME figure out where to source this
 }
+
+// Valid BLE TX power levels as per nRF52840 Product Specification are: "-20 to +8 dBm TX power, configurable in 4 dB steps".
+// See https://docs.nordicsemi.com/bundle/ps_nrf52840/page/keyfeatures_html5.html
+#define VALID_BLE_TX_POWER(x) \
+    ((x) == -20 || (x) == -16 || (x) == -12 || \
+     (x) == -8  || (x) == -4  || (x) == 0  || \
+     (x) == 4  || (x) == 8)
+
 void NRF52Bluetooth::setup()
 {
     // Initialise the Bluefruit module
@@ -251,6 +259,9 @@ void NRF52Bluetooth::setup()
     Bluefruit.Advertising.stop();
     Bluefruit.Advertising.clearData();
     Bluefruit.ScanResponse.clearData();
+#if defined(NRF52_BLE_TX_POWER) && VALID_BLE_TX_POWER(NRF52_BLE_TX_POWER)
+    Bluefruit.setTxPower(NRF52_BLE_TX_POWER);
+#endif
     if (config.bluetooth.mode != meshtastic_Config_BluetoothConfig_PairingMode_NO_PIN) {
         configuredPasskey = config.bluetooth.mode == meshtastic_Config_BluetoothConfig_PairingMode_FIXED_PIN
                                 ? config.bluetooth.fixed_pin

variants/nrf52840/heltec_mesh_node_t114/variant.h

@@ -150,6 +150,14 @@ No longer populated on PCB
 #define PIN_SPI1_MOSI ST7789_SDA
 #define PIN_SPI1_SCK ST7789_SCK
 
+/*
+ * Bluetooth
+ */
+
+// The bluetooth transmit power on the nRF52840 is adjustable from -20dB to +8dB in steps of 4dB
+// so NRF52_BLE_TX_POWER can be set to -20, -16, -12, -8, -4, 0 (default), 4, and 8.
+//#define NRF52_BLE_TX_POWER 8
+
 /*
  * GPS pins
  */