diff --git a/MAINTAINER_NOTES.md b/MAINTAINER_NOTES.md
new file mode 100644
index 0000000..127634e
--- /dev/null
+++ b/MAINTAINER_NOTES.md
@@ -0,0 +1,22 @@
+# Maintainer Notes
+
+## 2026-06-09 maintenance branch
+
+This branch is intentionally kept on the `2.5.1` release line so behavior can be tested against the published release without introducing a new public version number.
+
+The maintenance goals are:
+
+- align the Arduino Library Manager metadata and in-code version macros with release `v2.5.1`
+- make sensor index checks reject `sensorIndex == SensorCount`
+- make `sawNewSample()` match its documented behavior when hardware timers are used
+- align timer setup, pause, and resume platform macros for nRF52 and Due
+- fix small timer setup issues found by inspection before adding broader compile coverage
+- add an end-user ZIP install smoke test so the branch can be tested like an Arduino IDE library install
+- add a manual hardware test plan and draft `2.5.2` release notes for the next maintainer pass
+
+Open follow-up areas:
+
+- Add GitHub Actions smoke tests for supported Arduino cores that can be compiled automatically. A workflow file was prepared during this branch, but pushing `.github/workflows/arduino-compile.yml` requires a GitHub token with `workflow` scope.
+- Expand CI to optional examples that require display, websocket, Bluetooth, and web server dependencies.
+- Decide whether Servo timer selection should depend on `Servo.h` being included by the sketch instead of merely available in the installed core.
+- Add board-specific manual test notes for Pulse Transit Time and speaker/tone timer interactions.
diff --git a/library.properties b/library.properties
index 04fb809..990738c 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=PulseSensor Playground
-version=2.5.0
+version=2.5.1
 author=Joel Murphy, Yury Gitman, Brad Needham
 maintainer=Joel Murphy, Yury Gitman
 sentence=Support at PulseSensor.com
diff --git a/resources/EndUserInstallTesting.md b/resources/EndUserInstallTesting.md
new file mode 100644
index 0000000..2541f9e
--- /dev/null
+++ b/resources/EndUserInstallTesting.md
@@ -0,0 +1,41 @@
+# End User Install Testing
+
+Use this test before merging changes that might affect Arduino IDE users.
+
+The goal is to verify the library the way an end user gets it: as an installed Arduino library, not as a checked-out source tree.
+
+## ZIP install smoke test
+
+Run this from the repository root:
+
+```sh
+scripts/end-user-install-test.sh
+```
+
+The script:
+
+1. creates a ZIP from the current Git commit
+2. installs that ZIP into a temporary Arduino sketchbook
+3. compiles examples from the installed library folder
+
+By default it compiles `PulseSensor_XIAO_ESP32S3_BPM` for `esp32:esp32:XIAO_ESP32S3`, because that catches the current ESP32-S3 support path without requiring optional display or web server libraries.
+
+## Broader board matrix
+
+Set `PULSE_SENSOR_END_USER_MATRIX` to run more boards. Each line uses:
+
+```text
+name|core|fqbn|sketch|additional_board_manager_urls
+```
+
+Example:
+
+```sh
+PULSE_SENSOR_INSTALL_CORES=1 PULSE_SENSOR_END_USER_MATRIX='Uno BPM|arduino:avr|arduino:avr:uno|examples/PulseSensor_BPM|
+Mega two-sensor|arduino:avr|arduino:avr:mega|examples/TwoPulseSensors_On_OneArduino|
+UNO R4 WiFi plotter|arduino:renesas_uno|arduino:renesas_uno:unor4wifi|examples/PulseSensor_UNO_R4_WiFi_LEDmatrix_Plotter|
+XIAO ESP32-S3 BPM|esp32:esp32|esp32:esp32:XIAO_ESP32S3|examples/PulseSensor_XIAO_ESP32S3_BPM|https://espressif.github.io/arduino-esp32/package_esp32_index.json' \
+scripts/end-user-install-test.sh
+```
+
+Some optional examples require extra libraries such as display, websocket, Bluetooth, or async web server packages. Keep those in a separate optional matrix so the core library install test remains focused and dependable.
diff --git a/resources/MaintenanceBranchHandoff.md b/resources/MaintenanceBranchHandoff.md
new file mode 100644
index 0000000..1320084
--- /dev/null
+++ b/resources/MaintenanceBranchHandoff.md
@@ -0,0 +1,126 @@
+# Maintenance Branch Handoff
+
+Branch:
+
+```text
+codex/maintenance-traceability-ci
+```
+
+Draft PR:
+
+```text
+https://github.com/WorldFamousElectronics/PulseSensorPlayground/pull/207
+```
+
+## Current State
+
+The remote PR branch includes:
+
+- timer and bounds maintenance fixes
+- version metadata alignment to `2.5.1`
+- maintainer notes
+- end-user ZIP install smoke test
+- manual hardware test plan
+- draft `2.5.2` release notes
+
+The local branch has one extra commit that is not pushed:
+
+```text
+7e624af Add Arduino compile smoke workflow
+```
+
+That commit adds:
+
+```text
+.github/workflows/arduino-compile.yml
+```
+
+It is local-only because GitHub rejects workflow-file pushes unless the token has `workflow` scope.
+
+## Workflow Auth Step
+
+When a maintainer is available, run:
+
+```sh
+gh auth refresh -h github.com -s workflow
+```
+
+Complete the GitHub browser/device-code approval. Then push:
+
+```sh
+cd /Users/narwhal2/Documents/PulseSensorPlayground
+git push
+```
+
+If the local branch is not checked out:
+
+```sh
+cd /Users/narwhal2/Documents/PulseSensorPlayground
+git switch codex/maintenance-traceability-ci
+git push
+```
+
+## Local Validation Already Run
+
+Basic checks:
+
+```sh
+git diff --check
+ruby -e 'require "yaml"; YAML.load_file(".github/workflows/arduino-compile.yml"); puts "YAML OK"'
+```
+
+End-user install check:
+
+```sh
+scripts/end-user-install-test.sh
+```
+
+Expanded installed-library compile matrix on `esp32:esp32:XIAO_ESP32S3`:
+
+- `GettingStartedProject`
+- `Getting_BPM_to_Monitor`
+- `PulseSensor_BPM`
+- `PulseSensor_Pulse_Transit_Time`
+- `TwoPulseSensors_On_OneArduino`
+- `PulseSensor_XIAO_ESP32S3_BPM`
+
+The test installs a ZIP of the current commit into a temporary Arduino sketchbook and compiles from the installed library folder.
+
+## Known Local Limitation
+
+AVR and UNO R4 compiles were attempted locally, but this Mac's installed Arduino toolchains fail before compilation with:
+
+```text
+bad CPU type in executable
+```
+
+Use the GitHub Actions workflow or another machine to validate:
+
+- `arduino:avr:uno`
+- `arduino:avr:mega`
+- `arduino:renesas_uno:unor4wifi`
+
+## Hardware Still Needed
+
+Run the checklist in:
+
+```text
+resources/ManualHardwareTestPlan.md
+```
+
+Highest-value first pass:
+
+1. Arduino Uno R3 or Nano with `PulseSensor_BPM`
+2. XIAO ESP32-S3 with `PulseSensor_XIAO_ESP32S3_BPM`
+3. UNO R4 WiFi with LED matrix plotter
+4. Two-sensor PTT setup
+
+## Related Docs PR
+
+Separate draft PR:
+
+```text
+https://github.com/WorldFamousElectronics/PulseSensorPlayground/pull/208
+```
+
+That PR links WebSerial and CYD resources without mixing them into the maintenance-fix PR.
diff --git a/resources/ManualHardwareTestPlan.md b/resources/ManualHardwareTestPlan.md
new file mode 100644
index 0000000..f5b8029
--- /dev/null
+++ b/resources/ManualHardwareTestPlan.md
@@ -0,0 +1,105 @@
+# Manual Hardware Test Plan
+
+Use this checklist before merging or releasing maintenance changes to PulseSensor Playground.
+
+The goal is to confirm that the library works for end users after installation through Arduino IDE or a downloaded ZIP, not only from a developer checkout.
+
+## Install Path
+
+1. Download the branch ZIP:
+
+   ```text
+   https://github.com/WorldFamousElectronics/PulseSensorPlayground/archive/refs/heads/codex/maintenance-traceability-ci.zip
+   ```
+
+2. In Arduino IDE, use `Sketch > Include Library > Add .ZIP Library...`.
+3. Confirm examples appear under `File > Examples > PulseSensor Playground`.
+4. Open each target example from the Examples menu, not from the Git checkout.
+
+## Boards To Smoke Test
+
+### Arduino Uno R3 or Nano
+
+Examples:
+
+- `PulseSensor_BPM`
+- `PulseSensor_Speaker`
+- `TwoPulseSensors_On_OneArduino`
+
+Checks:
+
+- Upload succeeds.
+- Serial Plotter shows live samples.
+- BPM becomes non-zero after several clean beats.
+- LED blink follows `sawStartOfBeat()`.
+- Speaker example uses PWM-style beep behavior without `tone()` duration.
+
+### Arduino Mega 2560
+
+Example:
+
+- `TwoPulseSensors_On_OneArduino`
+
+Checks:
+
+- Upload succeeds.
+- Both channels produce independent sample traces.
+- Calling two-sensor methods does not hang or reset the board.
+- Out-of-range sensor indexes are ignored or return error values rather than reading past the sensor array.
+
+### Arduino UNO R4 WiFi
+
+Examples:
+
+- `PulseSensor_UNO_R4_WiFi_LEDmatrix_Plotter`
+- `PulseSensor_UNO_R4_WiFi_LEDmatrix_Heartbeat`
+
+Checks:
+
+- Upload succeeds.
+- LED matrix updates.
+- Serial Plotter output remains readable.
+- `pause()` / `resume()` can be tried manually if a small sketch is available.
+
+### Seeed XIAO ESP32-S3
+
+Example:
+
+- `PulseSensor_XIAO_ESP32S3_BPM`
+
+Checks:
+
+- Upload succeeds.
+- Serial Monitor reports BPM after clean beats.
+- `analogReadResolution(10)` behavior remains compatible with Playground's 0..1023 detector assumptions where examples use ESP32 ADC.
+
+### Pulse Transit Time Setup
+
+Example:
+
+- `PulseSensor_Pulse_Transit_Time`
+
+Checks:
+
+- Both sensors share the same voltage and ground.
+- Visualizer or Serial Plotter shows two clean waveforms.
+- PTT values change only when both channels detect beats.
+- Fingertip/earlobe placement gives cleaner signals than wrist placement.
+
+## Regression Areas
+
+- `sawNewSample()` should return `true` after hardware-timer samples.
+- `sensorIndex == SensorCount` should not access outside the sensor array.
+- `pause()` and `resume()` should return `true` on supported hardware timer platforms.
+- Unsupported boards should fall back to software timing with a compile warning.
+- Library version output should report `v2.5.1` while this branch remains a test branch.
+
+## Pass Criteria
+
+This maintenance branch is ready to merge when:
+
+- At least one AVR board passes.
+- XIAO ESP32-S3 passes.
+- UNO R4 WiFi passes, or any failure is documented as board-core/toolchain specific.
+- The branch ZIP install path works in Arduino IDE.
+- No example requires editing the installed library files to compile.
diff --git a/resources/ReleaseNotes-2.5.2-draft.md b/resources/ReleaseNotes-2.5.2-draft.md
new file mode 100644
index 0000000..602498b
--- /dev/null
+++ b/resources/ReleaseNotes-2.5.2-draft.md
@@ -0,0 +1,55 @@
+# PulseSensor Playground 2.5.2 Draft Release Notes
+
+This draft assumes the maintenance branch is tested and merged after `v2.5.1`.
+
+## Summary
+
+PulseSensor Playground 2.5.2 is a maintenance release focused on version traceability, timer behavior, bounds checks, and install-path testing.
+
+## Changes
+
+- Align `library.properties` and in-code version macros with the published `v2.5.1` baseline before the next version bump.
+- Fix sensor-index validation so `sensorIndex == SensorCount` is rejected instead of treated as valid.
+- Make `sawNewSample()` reflect hardware-timer samples as documented.
+- Align hardware timer pause/resume platform checks for nRF52 and Arduino Due.
+- Fix ESP8266 timer setup so it uses the shared timer object and returns success.
+- Fix ESP32 timer disable so `pause()` can report success.
+- Fix Arduino Mega timer disable mismatch when Timer2 is selected.
+- Guard Renesas timer setup if no timer is available after forcing PWM-reserved timer use.
+- Fix an ATtiny85 1 MHz timer setup typo.
+- Add an end-user ZIP install smoke test for Arduino IDE-style library installation.
+- Add manual hardware validation notes for release testing.
+
+## Testing Notes
+
+Automated/local:
+
+- `git diff --check`
+- XIAO ESP32-S3 BPM example compile with `arduino-cli`
+- ZIP install smoke test with `scripts/end-user-install-test.sh`
+- Remote GitHub branch ZIP install and compile smoke test
+- Expanded installed-library compile pass on `esp32:esp32:XIAO_ESP32S3`:
+  - `GettingStartedProject`
+  - `Getting_BPM_to_Monitor`
+  - `PulseSensor_BPM`
+  - `PulseSensor_Pulse_Transit_Time`
+  - `TwoPulseSensors_On_OneArduino`
+  - `PulseSensor_XIAO_ESP32S3_BPM`
+
+Manual hardware testing recommended before release:
+
+- Arduino Uno R3 or Nano
+- Arduino Mega 2560
+- Arduino UNO R4 WiFi
+- Seeed XIAO ESP32-S3
+- Two-sensor Pulse Transit Time setup
+
+## Release Process Notes
+
+After merge and hardware validation:
+
+1. Bump `library.properties` from `2.5.1` to `2.5.2`.
+2. Bump `PULSESENSOR_PLAYGROUND_VERSION_STRING` to `v2.5.2`.
+3. Bump `PULSESENSOR_PLAYGROUND_VERSION_NUMBER` to `252`.
+4. Tag the release as `v2.5.2`.
+5. Publish release notes using this draft as the starting point.
diff --git a/scripts/end-user-install-test.sh b/scripts/end-user-install-test.sh
new file mode 100755
index 0000000..4a26e3c
--- /dev/null
+++ b/scripts/end-user-install-test.sh
@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+tmp_dir="$(mktemp -d)"
+cleanup() {
+  rm -rf "$tmp_dir"
+}
+trap cleanup EXIT
+
+zip_path="$tmp_dir/PulseSensorPlayground.zip"
+sketchbook="$tmp_dir/sketchbook"
+config_file="$tmp_dir/arduino-cli.yaml"
+
+mkdir -p "$sketchbook"
+
+cat > "$config_file" <<EOF
+directories:
+  user: $sketchbook
+library:
+  enable_unsafe_install: true
+board_manager:
+  additional_urls:
+    - https://espressif.github.io/arduino-esp32/package_esp32_index.json
+EOF
+
+git -C "$repo_root" archive \
+  --format zip \
+  --prefix PulseSensorPlayground/ \
+  --output "$zip_path" \
+  HEAD
+
+arduino-cli --config-file "$config_file" lib install --zip-path "$zip_path"
+
+installed_library="$(find "$sketchbook/libraries" -maxdepth 1 -type d -name 'PulseSensor*' | head -n 1)"
+if [[ -z "$installed_library" ]]; then
+  echo "Could not find installed PulseSensor library in $sketchbook/libraries" >&2
+  exit 1
+fi
+
+default_matrix="XIAO ESP32-S3 BPM|esp32:esp32|esp32:esp32:XIAO_ESP32S3|examples/PulseSensor_XIAO_ESP32S3_BPM|https://espressif.github.io/arduino-esp32/package_esp32_index.json"
+matrix="${PULSE_SENSOR_END_USER_MATRIX:-$default_matrix}"
+
+while IFS='|' read -r name core fqbn sketch additional_urls; do
+  [[ -z "${name:-}" ]] && continue
+
+  if [[ "${PULSE_SENSOR_INSTALL_CORES:-0}" == "1" ]]; then
+    if [[ -n "${additional_urls:-}" ]]; then
+      arduino-cli --config-file "$config_file" core update-index --additional-urls "$additional_urls"
+      arduino-cli --config-file "$config_file" core install "$core" --additional-urls "$additional_urls"
+    else
+      arduino-cli --config-file "$config_file" core update-index
+      arduino-cli --config-file "$config_file" core install "$core"
+    fi
+  fi
+
+  echo "Compiling installed-library example: $name"
+  arduino-cli --config-file "$config_file" compile \
+    --fqbn "$fqbn" \
+    "$installed_library/$sketch" \
+    --warnings default
+done <<< "$matrix"
+
+echo "End-user ZIP install test passed for installed library: $installed_library"
diff --git a/src/PulseSensorPlayground.cpp b/src/PulseSensorPlayground.cpp
index ce971c6..94252d4 100644
--- a/src/PulseSensorPlayground.cpp
+++ b/src/PulseSensorPlayground.cpp
@@ -34,7 +34,7 @@ PulseSensorPlayground::PulseSensorPlayground(int numberOfSensors) {
 #endif
 
   // Dynamically create the array to minimize ram usage.
-  SensorCount = (byte) numberOfSensors;
+  SensorCount = (byte) constrain(numberOfSensors, 1, 255);
   Sensors = new PulseSensor[SensorCount];
 
 // set our internal variable to reflect hardware timer use
@@ -83,21 +83,21 @@ bool PulseSensorPlayground::PulseSensorPlayground::begin() {
 }
 
 void PulseSensorPlayground::analogInput(int inputPin, int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return; // out of range.
   }
   Sensors[sensorIndex].analogInput(inputPin);
 }
 
 void PulseSensorPlayground::blinkOnPulse(int blinkPin, int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return; // out of range.
   }
   Sensors[sensorIndex].blinkOnPulse(blinkPin);
 }
 
 void PulseSensorPlayground::fadeOnPulse(int fadePin, int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return; // out of range.
   }
   Sensors[sensorIndex].fadeOnPulse(fadePin);
@@ -117,10 +117,10 @@ bool PulseSensorPlayground::sawNewSample() {
   if(!Paused){
     if (UsingHardwareTimer) {
       // Disable interrupts to avoid a race with the ISR.
-      // DISABLE_PULSE_SENSOR_INTERRUPTS;
+      DISABLE_PULSE_SENSOR_INTERRUPTS;
       bool sawOne = SawNewSample;
       SawNewSample = false;
-      // ENABLE_PULSE_SENSOR_INTERRUPTS;
+      ENABLE_PULSE_SENSOR_INTERRUPTS;
 
       result = sawOne;
     } else { 
@@ -166,46 +166,51 @@ void PulseSensorPlayground::onSampleTime() {
   }
 
   // Set the flag that says we've read a sample since the Sketch checked.
+  SawNewSample = true;
   // digitalWrite(timingPin,LOW); // optionally connect timingPin to oscilloscope to time algorithm run time
  }
 
+bool PulseSensorPlayground::isValidSensorIndex(int sensorIndex) {
+  return sensorIndex >= 0 && sensorIndex < SensorCount;
+}
+
 int PulseSensorPlayground::getLatestSample(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return -1; // out of range.
   }
   return Sensors[sensorIndex].getLatestSample();
 }
 
 int PulseSensorPlayground::getBeatsPerMinute(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return -1; // out of range.
   }
   return Sensors[sensorIndex].getBeatsPerMinute();
 }
 
 int PulseSensorPlayground::getInterBeatIntervalMs(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return -1; // out of range.
   }
   return Sensors[sensorIndex].getInterBeatIntervalMs();
 }
 
 bool PulseSensorPlayground::sawStartOfBeat(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return false; // out of range.
   }
   return Sensors[sensorIndex].sawStartOfBeat();
 }
 
 bool PulseSensorPlayground::isInsideBeat(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return false; // out of range.
   }
   return Sensors[sensorIndex].isInsideBeat();
 }
 
 void PulseSensorPlayground::setThreshold(int threshold, int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return; // out of range.
   }
   Sensors[sensorIndex].setThreshold(threshold);
@@ -236,14 +241,14 @@ void PulseSensorPlayground::setThreshold(int threshold, int sensorIndex) {
 #endif
 
 int PulseSensorPlayground::getPulseAmplitude(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return -1; // out of range.
   }
   return Sensors[sensorIndex].getPulseAmplitude();
 }
 
 unsigned long PulseSensorPlayground::getLastBeatTime(int sensorIndex) {
-  if (sensorIndex != constrain(sensorIndex, 0, SensorCount)) {
+  if (!isValidSensorIndex(sensorIndex)) {
     return -1; // out of range.
   }
   return Sensors[sensorIndex].getLastBeatTime();
@@ -440,7 +445,7 @@ bool PulseSensorPlayground::setupInterrupt(){
     #elif F_CPU == 8000000L
       TCCR1 = 0x88;      // Clear Timer on Compare, Set Prescaler to 128
         #elif F_CPU == 1000000L
-            TCCR1 = 0x85            // Clear Timer on Compare, Set Prescaler to 16
+            TCCR1 = 0x85;           // Clear Timer on Compare, Set Prescaler to 16
     #endif
     bitSet(TIMSK,6);   // Enable interrupt on match between TCNT1 and OCR1A
     ENABLE_PULSE_SENSOR_INTERRUPTS;
@@ -450,15 +455,17 @@ bool PulseSensorPlayground::setupInterrupt(){
   #if defined(ARDUINO_ARCH_RENESAS)
     uint8_t timer_type = GPT_TIMER;
     int8_t tindex = FspTimer::get_available_timer(timer_type);
-    if(tindex == 0){
+    if(tindex < 0){
         FspTimer::force_use_of_pwm_reserved_timer();
         tindex = FspTimer::get_available_timer(timer_type);  
     }
-    sampleTimer.begin(TIMER_MODE_PERIODIC, timer_type, tindex, SAMPLE_RATE_500HZ, 0.0f, sampleTimerISR);
-    sampleTimer.setup_overflow_irq();
-    sampleTimer.open();
-    sampleTimer.start();
-    result = true;
+    if(tindex >= 0){
+      sampleTimer.begin(TIMER_MODE_PERIODIC, timer_type, tindex, SAMPLE_RATE_500HZ, 0.0f, sampleTimerISR);
+      sampleTimer.setup_overflow_irq();
+      sampleTimer.open();
+      sampleTimer.start();
+      result = true;
+    }
   #endif
 
   #if defined(ARDUINO_SAM_DUE)
@@ -497,9 +504,9 @@ bool PulseSensorPlayground::setupInterrupt(){
   #endif
 
   #if defined(ARDUINO_ARCH_ESP8266)
-        ESP8266Timer sampleTimer;
     sampleTimer.setFrequency(500,onInterrupt);
     sampleTimer.restartTimer();
+    result = true;
   #endif
 
   #if defined(ARDUINO_SAMD_ZERO) || defined(ARDUINO_ARCH_SAMD)
@@ -566,7 +573,7 @@ bool PulseSensorPlayground::enableInterrupt(){
     result = true;
   #endif
 
-  #if defined(ARDUINO_ARCH_NRF52840)
+  #if defined(ARDUINO_NRF52_ADAFRUIT)
     sampleTimer.restartTimer();
     result = true;
   #endif
@@ -586,7 +593,7 @@ bool PulseSensorPlayground::enableInterrupt(){
     result = true;
   #endif
 
-  #if defined(ARDUINO_ARCH_SAM)
+  #if defined(ARDUINO_SAM_DUE)
     sampleTimer.start(2000);
     result = true;
   #endif
@@ -631,7 +638,7 @@ bool PulseSensorPlayground::disableInterrupt(){
         result = true;
     #else
         DISABLE_PULSE_SENSOR_INTERRUPTS;
-        TIMSK3 = 0x00;          // Disable OCR2A match interrupt
+        TIMSK2 = 0x00;          // Disable OCR2A match interrupt
         ENABLE_PULSE_SENSOR_INTERRUPTS;
         result = true;
     #endif
@@ -646,9 +653,10 @@ bool PulseSensorPlayground::disableInterrupt(){
 
   #if defined(ARDUINO_ARCH_ESP32)
     timerStop(sampleTimer);
+    result = true;
   #endif
 
-  #if defined(ARDUINO_ARCH_NRF52840)
+  #if defined(ARDUINO_NRF52_ADAFRUIT)
     sampleTimer.stopTimer();
     result = true;
   #endif
@@ -668,7 +676,7 @@ bool PulseSensorPlayground::disableInterrupt(){
     result = true;
   #endif
 
-  #if defined(ARDUINO_ARCH_SAM)
+  #if defined(ARDUINO_SAM_DUE)
     sampleTimer.stop();
     result = true;
   #endif
diff --git a/src/PulseSensorPlayground.h b/src/PulseSensorPlayground.h
index 8a8821a..bb91fb3 100644
--- a/src/PulseSensorPlayground.h
+++ b/src/PulseSensorPlayground.h
@@ -33,8 +33,8 @@
 /*
     Library version number
 */
-#define PULSESENSOR_PLAYGROUND_VERSION_STRING "v2.1.0"
-#define PULSESENSOR_PLAYGROUND_VERSION_NUMBER 210
+#define PULSESENSOR_PLAYGROUND_VERSION_STRING "v2.5.1"
+#define PULSESENSOR_PLAYGROUND_VERSION_NUMBER 251
 
 /*
    If you wish to perform timing statistics on your non-interrupt Sketch:
@@ -443,6 +443,7 @@ vvvvvvvv  THIS NEEDS MODIFICATION FOR V2 vvvvvvvv
 bool setupInterrupt();
 bool disableInterrupt();
 bool enableInterrupt();
+bool isValidSensorIndex(int sensorIndex);
 
 /*
    Varialbles