diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..24f136b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*/*.wasm
+*/wokwi-api.h
diff --git a/heart_rate/Makefile b/heart_rate/Makefile
new file mode 100644
index 0000000..cbb3f80
--- /dev/null
+++ b/heart_rate/Makefile
@@ -0,0 +1,75 @@
+# Wokwi Custom Chip Makefile
+# Generated by wokwi-cli
+#
+# Usage:
+#   make          - Build the chip
+#   make clean    - Remove build artifacts
+#   make wokwi-api.h - Download the Wokwi API header
+#
+# Requirements:
+#   - WASI-SDK (https://github.com/WebAssembly/wasi-sdk)
+#   - Set WASI_SDK_PATH environment variable or install to ~/.wokwi/wasi-sdk
+#
+
+# Configuration
+CHIP_NAME ?= heartrate.chip
+SOURCES ?= main.c
+OUTPUT ?= $(CHIP_NAME).wasm
+
+# WASI-SDK paths
+WASI_SDK_PATH ?= /l/disk0/alopes/.wokwi/wasi-sdk
+WASI_SDK_VERSION ?= 25
+
+# Compiler settings
+CC = $(WASI_SDK_PATH)/bin/clang
+SYSROOT = $(WASI_SDK_PATH)/share/wasi-sysroot
+
+# Compilation flags
+CFLAGS = --target=wasm32-wasi \
+         --sysroot=$(SYSROOT) \
+         -nostartfiles \
+         -I. \
+         -O2
+
+LDFLAGS = -Wl,--no-entry \
+          -Wl,--import-memory \
+          -Wl,--export-table
+
+# Default target
+all: check-sdk wokwi-api.h $(OUTPUT)
+
+# Build the WASM file
+$(OUTPUT): $(SOURCES) wokwi-api.h
+	@echo "Compiling $(CHIP_NAME)..."
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(SOURCES)
+	@echo "Success! Output: $@ ($$(du -h $@ | cut -f1))"
+
+# Check WASI-SDK is available
+check-sdk:
+	@if [ ! -d "$(WASI_SDK_PATH)" ]; then \
+		echo "Error: WASI-SDK not found at $(WASI_SDK_PATH)"; \
+		echo ""; \
+		echo "Install WASI-SDK:"; \
+		echo "  Option 1: Run 'wokwi-cli chip compile' once to auto-install"; \
+		echo "  Option 2: Download from https://github.com/WebAssembly/wasi-sdk/releases"; \
+		echo "  Option 3: Set WASI_SDK_PATH environment variable"; \
+		exit 1; \
+	fi
+
+# Download wokwi-api.h if not present
+wokwi-api.h:
+	@if [ ! -f wokwi-api.h ]; then \
+		echo "Downloading wokwi-api.h..."; \
+		curl -sL "https://wokwi.com/api/chips/wokwi-api.h" -o wokwi-api.h; \
+		echo "Downloaded wokwi-api.h"; \
+	fi
+
+# Clean build artifacts
+clean:
+	rm -f $(OUTPUT)
+
+# Clean everything including downloaded files
+distclean: clean
+	rm -f wokwi-api.h
+
+.PHONY: all check-sdk clean distclean
diff --git a/heart_rate/heartrate.chip.json b/heart_rate/heartrate.chip.json
new file mode 100644
index 0000000..840a00c
--- /dev/null
+++ b/heart_rate/heartrate.chip.json
@@ -0,0 +1,11 @@
+{
+  "name": "heartrate",
+  "author": "Amaro Lopes",
+  "pins": [
+    "VCC",
+    "GND",
+    "BTN",
+    "OUT"
+  ],
+  "controls": []
+}
diff --git a/heart_rate/main.c b/heart_rate/main.c
new file mode 100644
index 0000000..7296274
--- /dev/null
+++ b/heart_rate/main.c
@@ -0,0 +1,119 @@
+
+#include "wokwi-api.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+/* -------------------------------------------------- */
+/* States */
+
+typedef enum { STATE_NORMAL, STATE_RISING, STATE_FALLING } hr_state_t;
+
+typedef enum { STATE_SLOW = 0, STATE_FAST = 1 } hr_speed_t;
+
+/* -------------------------------------------------- */
+/* Chip state */
+
+typedef struct {
+  pin_t out_pin;
+  pin_t btn_pin;
+
+  float bpm;
+  int last_target;
+
+  hr_state_t state;
+  hr_speed_t speed;
+
+  int pulseValue;
+
+  timer_t update_timer;
+} chip_state_t;
+
+/* -------------------------------------------------- */
+/* Output mapping */
+
+static void update_output_voltage(chip_state_t *chip) {
+  float volts = (chip->bpm * 3.3f) / 675.0f;
+
+  if (volts < 0.0f)
+    volts = 0.0f;
+  if (volts > 3.3f)
+    volts = 3.3f;
+
+  pin_dac_write(chip->out_pin, volts);
+
+  printf("BPM: %.1f | Voltage: %.3fV\n", chip->bpm, volts);
+}
+
+/* -------------------------------------------------- */
+/* Main update loop */
+
+static void update_cb(void *user_data) {
+  chip_state_t *chip = user_data;
+
+  int target = attr_read(chip->pulseValue);
+
+  /* Read pull-down switch: LOW=SLOW, HIGH=FAST */
+  chip->speed = pin_read(chip->btn_pin) ? STATE_FAST : STATE_SLOW;
+
+  /* Detect target change and re-evaluate direction */
+  if (target != chip->last_target) {
+    if (chip->bpm < target) {
+      chip->state = STATE_RISING;
+    } else if (chip->bpm > target) {
+      chip->state = STATE_FALLING;
+    } else {
+      chip->state = STATE_NORMAL;
+    }
+    chip->last_target = target;
+  }
+
+  /* Step size */
+  float step = (chip->speed == STATE_FAST) ? 2.0f : 0.5f;
+
+  /* Rising */
+  if (chip->state == STATE_RISING) {
+    chip->bpm += step;
+    if (chip->bpm >= target) {
+      chip->bpm = target;
+      chip->state = STATE_NORMAL;
+    }
+  }
+
+  /* Falling */
+  if (chip->state == STATE_FALLING) {
+    chip->bpm -= step;
+    if (chip->bpm <= target) {
+      chip->bpm = target;
+      chip->state = STATE_NORMAL;
+    }
+  }
+
+  update_output_voltage(chip);
+}
+
+/* -------------------------------------------------- */
+/* Init */
+
+void chip_init(void) {
+  printf("Heart Rate chip init\n");
+
+  chip_state_t *chip = calloc(1, sizeof(chip_state_t));
+
+  /* Attribute: target BPM */
+  chip->pulseValue = attr_init("pulseValue", 100);
+
+  chip->bpm = 100.0f;
+  chip->last_target = 100;
+  chip->state = STATE_NORMAL;
+  chip->speed = STATE_SLOW;
+
+  chip->out_pin = pin_init("OUT", ANALOG);
+  chip->btn_pin = pin_init("BTN", INPUT); // pull-down switch
+
+  timer_config_t update_cfg = {.callback = update_cb, .user_data = chip};
+
+  chip->update_timer = timer_init(&update_cfg);
+
+  /* 50 ms update rate */
+  timer_start(chip->update_timer, 50000, true);
+}