From 47809d3cafb26abf2fa9c8d05bc33852f21e0311 Mon Sep 17 00:00:00 2001
From: hbvanommen <h.b.vanommen@tudelft.nl>
Date: Sat, 10 Jan 2026 18:57:59 +0100
Subject: [PATCH 1/3] Battery level readout

---
 examples/Tap_to_Measure/Tap_to_Measure.ino |  6 +--
 src/Qbead.h                                | 33 +++++++++++++++-
 src/QbeadBattery.h                         | 45 ++++++++++++++++++++++
 3 files changed, 80 insertions(+), 4 deletions(-)
 create mode 100644 src/QbeadBattery.h

diff --git a/examples/Tap_to_Measure/Tap_to_Measure.ino b/examples/Tap_to_Measure/Tap_to_Measure.ino
index a2a52aa..1202a4d 100644
--- a/examples/Tap_to_Measure/Tap_to_Measure.ino
+++ b/examples/Tap_to_Measure/Tap_to_Measure.ino
@@ -38,9 +38,9 @@ void loop() {
 
   // Show the result.
   bead.show();
-
-  // ### Check for taps
-  if (bead.tapped) {
+  bead.measureBattery();
+  if (bead.wasTapped()){
+    total_taps++;
     bead.clear();
     BlochVector acc_vector(bead.x, bead.y, bead.z);
     float probability = pow(innerProductAbs(current_state, acc_vector),2);
diff --git a/src/Qbead.h b/src/Qbead.h
index f79318d..2cda037 100644
--- a/src/Qbead.h
+++ b/src/Qbead.h
@@ -8,6 +8,8 @@
 #include <math.h>
 
 #include <bluefruit.h>
+#include <QbeadBattery.h>
+
 
 // default configs
 // TODO make them ifndef
@@ -281,12 +283,16 @@ class Qbead {
         blecharcol(QB_UUID_COL_CHAR),
         blecharsph(QB_UUID_SPH_CHAR),
         blecharacc(QB_UUID_ACC_CHAR),
-        blechartap(QB_UUID_TAP_CHAR)
+        blechartap(QB_UUID_TAP_CHAR),
+        blecharbatlvl(UUID16_CHR_BATTERY_LEVEL)
         {}
 
   static Qbead *singletoninstance; // we need a global singleton static instance because bluefruit callbacks do not support context variables -- thankfully this is fine because there is indeed only one Qbead in existence at any time
 
   LSM6DS3 imu;
+
+  Xiao battery;
+
   Adafruit_NeoPixel pixels;
 
   BLEService bleservice;
@@ -294,6 +300,7 @@ class Qbead {
   BLECharacteristic blecharsph;
   BLECharacteristic blecharacc;
   BLECharacteristic blechartap;
+  BLECharacteristic blecharbatlvl;
   uint8_t connection_count = 0;
 
   const uint8_t nsections;
@@ -302,6 +309,7 @@ class Qbead {
   const uint8_t phi_quant;
   const uint8_t ix, iy, iz;
   const bool sx, sy, sz;
+  uint8_t bat_buff[1];
   float rbuffer[3];
   float x, y, z, rx, ry, rz; // filtered and raw acc, in units of g
   float t_acc, p_acc;        // theta and phi according to gravity
@@ -383,9 +391,32 @@ class Qbead {
     blechartap.setFixedLen(3*sizeof(float));
     blechartap.begin();
     blechartap.write(zerobuffer20, 3*sizeof(float));
+    // BLE Characteristic battery level
+    blecharbatlvl.setProperties(CHR_PROPS_READ | CHR_PROPS_NOTIFY);
+    blecharbatlvl.setPermission(SECMODE_OPEN, SECMODE_OPEN);
+    blecharbatlvl.setUserDescriptor("battery level");
+    blecharbatlvl.setFixedLen(1*sizeof(uint8_t));
+    blecharbatlvl.begin();
+    blecharbatlvl.write(zerobuffer20, sizeof(uint8_t));
     startBLEadv();
   }
 
+  void measureBattery(){
+    // if you measure the voltage twice in a row, the second time, the voltage will be 0.2V lower.
+    float percentage = battery.GetBatteryLevel();
+
+    float voltage = battery.GetBatteryVoltage();
+    bool charging = battery.IsChargingBattery();
+    bat_buff[0] = uint8_t(percentage);
+    Serial.println("battery voltage");
+    Serial.print(voltage);
+    Serial.print(", ");
+    Serial.print(charging);
+    Serial.print(", ");
+    Serial.println(percentage);
+    blecharbatlvl.write(bat_buff, sizeof(uint8_t));
+  }
+
   void clear() {
     pixels.clear();
   }
diff --git a/src/QbeadBattery.h b/src/QbeadBattery.h
new file mode 100644
index 0000000..0789ee2
--- /dev/null
+++ b/src/QbeadBattery.h
@@ -0,0 +1,45 @@
+#include <Arduino.h>
+#include <bluefruit.h>
+
+#define BAT_HIGH_CHARGE 22  // HIGH for 50mA, LOW for 100mA
+#define BAT_CHARGE_STATE 23 // LOW for charging, HIGH not charging
+
+class Xiao {
+public:
+  Xiao();
+  float GetBatteryVoltage();
+  bool IsChargingBattery();
+  float GetBatteryLevel();
+private:
+  // define min and max voltage for battery level determination
+  float maxVoltage = 4.11;
+  float minVoltage = 3.06;
+};
+
+Xiao::Xiao() {
+  pinMode(VBAT_ENABLE, OUTPUT);
+  pinMode(BAT_CHARGE_STATE, INPUT);
+
+  digitalWrite(BAT_HIGH_CHARGE, LOW); // charge with 100ma if LOW, else 50mA
+}
+
+#define VBAT_MV_PER_LBS (0.003395996F)
+
+float Xiao::GetBatteryVoltage() {
+  digitalWrite(VBAT_ENABLE, LOW);
+  // might want to wait very briefly for the voltage to settle
+  uint32_t adcCount = analogRead(PIN_VBAT);
+  float adcVoltage = adcCount * VBAT_MV_PER_LBS;
+  float vBat = adcVoltage * (1510.0 / 510.0);
+
+  digitalWrite(VBAT_ENABLE, HIGH);
+
+  return vBat;
+}
+
+float Xiao::GetBatteryLevel() {
+  float batPercentage = (GetBatteryVoltage()-minVoltage)/(maxVoltage - minVoltage) * 100;
+  return batPercentage;
+}
+
+bool Xiao::IsChargingBattery() { return digitalRead(BAT_CHARGE_STATE) == LOW; }
\ No newline at end of file

From 3c040046b93525be11d4b687788d7be90d337d89 Mon Sep 17 00:00:00 2001
From: hbvanommen <h.b.vanommen@tudelft.nl>
Date: Sat, 10 Jan 2026 19:36:59 +0100
Subject: [PATCH 2/3] Cleaning up

---
 examples/Tap_to_Measure/Tap_to_Measure.ino |  4 ++--
 src/Qbead.h                                |  2 +-
 src/QbeadBattery.h                         | 12 ++++++------
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/examples/Tap_to_Measure/Tap_to_Measure.ino b/examples/Tap_to_Measure/Tap_to_Measure.ino
index 1202a4d..3883a4f 100644
--- a/examples/Tap_to_Measure/Tap_to_Measure.ino
+++ b/examples/Tap_to_Measure/Tap_to_Measure.ino
@@ -38,9 +38,9 @@ void loop() {
 
   // Show the result.
   bead.show();
+  // for testing purposes just readout the battery level every loop now
   bead.measureBattery();
-  if (bead.wasTapped()){
-    total_taps++;
+  if (bead.tapped){
     bead.clear();
     BlochVector acc_vector(bead.x, bead.y, bead.z);
     float probability = pow(innerProductAbs(current_state, acc_vector),2);
diff --git a/src/Qbead.h b/src/Qbead.h
index 2cda037..3cac759 100644
--- a/src/Qbead.h
+++ b/src/Qbead.h
@@ -291,7 +291,7 @@ class Qbead {
 
   LSM6DS3 imu;
 
-  Xiao battery;
+  XiaoBattery battery;
 
   Adafruit_NeoPixel pixels;
 
diff --git a/src/QbeadBattery.h b/src/QbeadBattery.h
index 0789ee2..2961bbe 100644
--- a/src/QbeadBattery.h
+++ b/src/QbeadBattery.h
@@ -4,9 +4,9 @@
 #define BAT_HIGH_CHARGE 22  // HIGH for 50mA, LOW for 100mA
 #define BAT_CHARGE_STATE 23 // LOW for charging, HIGH not charging
 
-class Xiao {
+class XiaoBattery {
 public:
-  Xiao();
+  XiaoBattery();
   float GetBatteryVoltage();
   bool IsChargingBattery();
   float GetBatteryLevel();
@@ -16,7 +16,7 @@ class Xiao {
   float minVoltage = 3.06;
 };
 
-Xiao::Xiao() {
+XiaoBattery::XiaoBattery() {
   pinMode(VBAT_ENABLE, OUTPUT);
   pinMode(BAT_CHARGE_STATE, INPUT);
 
@@ -25,7 +25,7 @@ Xiao::Xiao() {
 
 #define VBAT_MV_PER_LBS (0.003395996F)
 
-float Xiao::GetBatteryVoltage() {
+float XiaoBattery::GetBatteryVoltage() {
   digitalWrite(VBAT_ENABLE, LOW);
   // might want to wait very briefly for the voltage to settle
   uint32_t adcCount = analogRead(PIN_VBAT);
@@ -37,9 +37,9 @@ float Xiao::GetBatteryVoltage() {
   return vBat;
 }
 
-float Xiao::GetBatteryLevel() {
+float XiaoBattery::GetBatteryLevel() {
   float batPercentage = (GetBatteryVoltage()-minVoltage)/(maxVoltage - minVoltage) * 100;
   return batPercentage;
 }
 
-bool Xiao::IsChargingBattery() { return digitalRead(BAT_CHARGE_STATE) == LOW; }
\ No newline at end of file
+bool XiaoBattery::IsChargingBattery() { return digitalRead(BAT_CHARGE_STATE) == LOW; }
\ No newline at end of file

From 30e0b45f24eb2fd36859e5dd5fbbae4d8ef50091 Mon Sep 17 00:00:00 2001
From: hbvanommen <h.b.vanommen@tudelft.nl>
Date: Wed, 14 Jan 2026 11:03:02 +0100
Subject: [PATCH 3/3] Prototype for reporting battery level in html page

---
 QBeadVisualisation.html | 29 ++++++++++++++++++++++++++++-
 src/Qbead.h             |  2 +-
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/QBeadVisualisation.html b/QBeadVisualisation.html
index 62486b1..d3f74a8 100644
--- a/QBeadVisualisation.html
+++ b/QBeadVisualisation.html
@@ -27,6 +27,7 @@
         </div>
 
         <h3>Live Output</h3>
+        <p id="batteryLevel"></p>
         <div id="output" class="output" style="display: inline;">
           <div id="content"></div>
           <div id="status"></div>
@@ -313,6 +314,7 @@ <h3>Live Output</h3>
             var accCharacteristic;
             var sphCharacteristic;
             var colCharacteristic;
+            var batteryLevelCharacteristic;
             
             function onStartButtonClick() {
               let serviceUuid = "e30c1fc6-359c-12be-2544-63d6aa088d45";
@@ -320,7 +322,8 @@ <h3>Live Output</h3>
               let accUuid = "e30c1fc9-359c-12be-2544-63d6aa088d45";
               let sphUuid = "e30c1fc8-359c-12be-2544-63d6aa088d45";
               let colUuid = "e30c1fc7-359c-12be-2544-63d6aa088d45";
-            
+              let batUuid = "00002a19-0000-1000-8000-00805f9b34fb";
+
               log('Requesting Bluetooth Device...');
               navigator.bluetooth.requestDevice(
                 {
@@ -338,6 +341,13 @@ <h3>Live Output</h3>
               .then(service => {
                 log('Getting Characteristics...');
                 service.getCharacteristic(colUuid).then(ch => {colCharacteristic=ch;});
+                service.getCharacteristic(batUuid).then(ch => {
+                    batteryLevelCharacteristic=ch;
+                    return batteryLevelCharacteristic.startNotifications().then(_ => {
+                        batteryLevelCharacteristic.addEventListener('characteristicvaluechanged',
+                      handleBatteryNotifications);
+                    })
+                });
                 return service.getCharacteristic(accUuid);
               })
               .then(characteristic => {
@@ -365,6 +375,17 @@ <h3>Live Output</h3>
                   log('Argh! ' + error);
                 });
               }
+              if (batteryLevelCharacteristic) {
+                batteryLevelCharacteristic.stopNotifications()
+                .then(_ => {
+                  log('> Notifications stopped');
+                  batteryLevelCharacteristic.removeEventListener('characteristicvaluechanged',
+                      handleBatteryNotifications);
+                })
+                .catch(error => {
+                  log('Argh! ' + error);
+                });
+              }
             }
             
             function onPhiRangeChange() {
@@ -408,6 +429,12 @@ <h3>Live Output</h3>
               window.z = z;
               log(`> ${x.toFixed(3)} ${y.toFixed(3)} ${z.toFixed(3)} ${t.toFixed(0)} ${p.toFixed(0)} `);
             }
+
+            function handleBatteryNotifications(event) {
+              let batteryPercentage = event.target.value.getInt8(0);
+              document.getElementById("batteryLevel").textContent = `Battery Level:  ${batteryPercentage}%`;
+              // log(`> ${batteryPercentage} `);
+            }
             </script>
             
             
diff --git a/src/Qbead.h b/src/Qbead.h
index 3cac759..9dd809d 100644
--- a/src/Qbead.h
+++ b/src/Qbead.h
@@ -414,7 +414,7 @@ class Qbead {
     Serial.print(charging);
     Serial.print(", ");
     Serial.println(percentage);
-    blecharbatlvl.write(bat_buff, sizeof(uint8_t));
+    blecharbatlvl.notify(bat_buff, sizeof(uint8_t));
   }
 
   void clear() {