add ability to get battery voltage

index.html

@@ -101,6 +101,9 @@
                 <button @click="reboot" class="border border-gray-500 px-2 bg-gray-100 hover:bg-gray-200 rounded">
                     Reboot
                 </button>
+                <button @click="getBatteryVoltage" class="border border-gray-500 px-2 bg-gray-100 hover:bg-gray-200 rounded">
+                    GetBatteryVoltage
+                </button>
             </div>
         </div>
 
@@ -393,6 +396,14 @@
                     alert("Failed to reboot!");
                 }
             },
+            async getBatteryVoltage() {
+                try {
+                    const response = await this.connection.getBatteryVoltage();
+                    alert(`Battery Voltage: ${response.batteryMilliVolts}mV`);
+                } catch(e) {
+                    alert("Failed to get battery voltage!");
+                }
+            },
             bytesToHex(uint8Array) {
                 return Array.from(uint8Array).map(byte => byte.toString(16).padStart(2, '0')).join('');
             },

src/connection/connection.js

@@ -178,6 +178,12 @@ class Connection extends EventEmitter {
         await this.sendToRadioFrame(data.toBytes());
     }
 
+    async sendCommandGetBatteryVoltage() {
+        const data = new BufferWriter();
+        data.writeByte(Constants.CommandCodes.GetBatteryVoltage);
+        await this.sendToRadioFrame(data.toBytes());
+    }
+
     onFrameReceived(frame) {
 
         // emit received frame
@@ -210,6 +216,8 @@ class Connection extends EventEmitter {
             this.onSentResponse(bufferReader);
         } else if(responseCode === Constants.ResponseCodes.ExportContact){
             this.onExportContactResponse(bufferReader);
+        } else if(responseCode === Constants.ResponseCodes.BatteryVoltage){
+            this.onBatteryVoltageResponse(bufferReader);
         } else if(responseCode === Constants.PushCodes.Advert){
             this.onAdvertPush(bufferReader);
         } else if(responseCode === Constants.PushCodes.PathUpdated){
@@ -302,6 +310,12 @@ class Connection extends EventEmitter {
         });
     }
 
+    onBatteryVoltageResponse(bufferReader) {
+        this.emit(Constants.ResponseCodes.BatteryVoltage, {
+            batteryMilliVolts: bufferReader.readUInt16LE(),
+        });
+    }
+
     onSelfInfoResponse(bufferReader) {
         this.emit(Constants.ResponseCodes.SelfInfo, {
             type: bufferReader.readByte(),
@@ -972,6 +986,37 @@ class Connection extends EventEmitter {
         });
     }
 
+    getBatteryVoltage() {
+        return new Promise(async (resolve, reject) => {
+            try {
+
+                // resolve promise when we receive battery voltage
+                const onBatteryVoltage = (response) => {
+                    this.off(Constants.ResponseCodes.BatteryVoltage, onBatteryVoltage);
+                    this.off(Constants.ResponseCodes.Err, onErr);
+                    resolve(response);
+                }
+
+                // reject promise when we receive err
+                const onErr = () => {
+                    this.off(Constants.ResponseCodes.BatteryVoltage, onBatteryVoltage);
+                    this.off(Constants.ResponseCodes.Err, onErr);
+                    reject();
+                }
+
+                // listen for events
+                this.once(Constants.ResponseCodes.BatteryVoltage, onBatteryVoltage);
+                this.once(Constants.ResponseCodes.Err, onErr);
+
+                // get battery voltage
+                await this.sendCommandGetBatteryVoltage();
+
+            } catch(e) {
+                reject(e);
+            }
+        });
+    }
+
 }
 
 export default Connection;

src/constants.js

@@ -31,6 +31,7 @@ class Constants {
         ExportContact: 17,
         ImportContact: 18,
         Reboot: 19,
+        GetBatteryVoltage: 20,
     }
 
     static ResponseCodes = {
@@ -46,6 +47,7 @@ class Constants {
         CurrTime: 9,
         NoMoreMessages: 10,
         ExportContact: 11,
+        BatteryVoltage: 12,
     }
 
     static PushCodes = {