diff --git a/.env.sample b/.env.sample
index 5fd9784..bb5c8bc 100644
--- a/.env.sample
+++ b/.env.sample
@@ -1 +1,2 @@
-MODULE_RTD8_LEVELS=01234567 #number of stack level (0-7) not separated
\ No newline at end of file
+MODULE_RTD8_LEVELS=01234567 #number of stack level (0-7) not separated
+MODULE_REL4HVI4_LEVELS=01234567 #number of stack level (0-7) not separated
\ No newline at end of file
diff --git a/README.md b/README.md
index aa47fe6..6fa4d02 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,20 @@
 # SequentMicrosystems_API
 
-API for sequent microsystems boards running on RaspberryPI
\ No newline at end of file
+API for sequent microsystems boards running on RaspberryPI
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
diff --git a/pdm.lock b/pdm.lock
index 237ec1e..01f9752 100644
--- a/pdm.lock
+++ b/pdm.lock
@@ -5,7 +5,7 @@
 groups = ["default"]
 strategy = ["cross_platform", "inherit_metadata"]
 lock_version = "4.5.0"
-content_hash = "sha256:f4f1e2189c6ffd6d794a2407d788e6716784556dfe8717566ece8e4c48e157e7"
+content_hash = "sha256:a386b1448f475cfd997f505d3dc55da73a888f9be06306adbabb701440ec7aa3"
 
 [[metadata.targets]]
 requires_python = ">=3.12"
@@ -68,15 +68,6 @@ files = [
     {file = "colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44"},
 ]
 
-[[package]]
-name = "dotenv"
-version = "0.0.5"
-summary = "Handle .env files"
-groups = ["default"]
-files = [
-    {file = "dotenv-0.0.5.tar.gz", hash = "sha256:b58d2ab3f83dbd4f8a362b21158a606bee87317a9444485566b3c8f0af847091"},
-]
-
 [[package]]
 name = "fastapi"
 version = "0.115.5"
@@ -193,6 +184,30 @@ files = [
     {file = "pydantic_core-2.27.0.tar.gz", hash = "sha256:f57783fbaf648205ac50ae7d646f27582fc706be3977e87c3c124e7a92407b10"},
 ]
 
+[[package]]
+name = "python-dotenv"
+version = "1.0.1"
+requires_python = ">=3.8"
+summary = "Read key-value pairs from a .env file and set them as environment variables"
+groups = ["default"]
+files = [
+    {file = "python-dotenv-1.0.1.tar.gz", hash = "sha256:e324ee90a023d808f1959c46bcbc04446a10ced277783dc6ee09987c37ec10ca"},
+    {file = "python_dotenv-1.0.1-py3-none-any.whl", hash = "sha256:f7b63ef50f1b690dddf550d03497b66d609393b40b564ed0d674909a68ebf16a"},
+]
+
+[[package]]
+name = "sm4relind"
+version = "1.0.3"
+summary = "A set of functions to control Sequent Microsystems 4-Relay board"
+groups = ["default"]
+dependencies = [
+    "smbus2",
+]
+files = [
+    {file = "SM4relind-1.0.3-py2.py3-none-any.whl", hash = "sha256:1308f580d05893f481b79c055dfb5572bbce992777edeee6292c91c707a73a55"},
+    {file = "sm4relind-1.0.3.tar.gz", hash = "sha256:aa1c464f6344be63f8a84fb7e51d9c683f73f696cb8fd43cb0f1171b851f7d6b"},
+]
+
 [[package]]
 name = "smbus2"
 version = "0.5.0"
diff --git a/pyproject.toml b/pyproject.toml
index 4381439..de5bf9c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,8 +8,9 @@ authors = [
 dependencies = [
     "fastapi>=0.115.5",
     "uvicorn>=0.32.1",
-    "dotenv>=0.0.5",
     "SMrtd>=1.0.1",
+    "SM4relind>=1.0.3",
+    "python-dotenv>=1.0.1",
 ]
 requires-python = ">=3.12"
 readme = "README.md"
diff --git a/src/main.py b/src/main.py
index 5e0298a..f2a6911 100644
--- a/src/main.py
+++ b/src/main.py
@@ -1,7 +1,14 @@
+import os
+from dotenv import load_dotenv
+
+load_dotenv()
+
 from fastapi import FastAPI
 from src.modules.router import router as modulesrouter
 
 
+
 app = FastAPI(root_path="/api")
 
 app.include_router(router=modulesrouter)
+
diff --git a/src/modules/RTD8/service.py b/src/modules/RTD8/service.py
index 00b1d96..c947d5a 100644
--- a/src/modules/RTD8/service.py
+++ b/src/modules/RTD8/service.py
@@ -5,6 +5,9 @@ stacks = [int(h) for h in os.getenv("MODULE_RTD8_LEVELS", "")]
 if not stacks:
     print("MODULE_RTD8_LEVELS is not set or invalid")
 
+for i in stacks:
+    print(f"Configured RTD8 card: {i}")
+
 
 
 def read_temp(stack: int, channel: int) -> float | str:
@@ -15,7 +18,7 @@ def read_temp(stack: int, channel: int) -> float | str:
         try:
             return librtd.get(stack, channel)
         except Exception as e:
-            raise ValueError(f"Error read data from card {stack} on channel {channel} by error: {e}")
+            return -512
     
     return -512
 
@@ -41,7 +44,7 @@ def read_resistance(stack: int, channel: int) -> float | str:
         try:
             return librtd.getRes(stack, channel)
         except Exception as e:
-            raise ValueError(f"Error read data from card {stack} on channel {channel} by error: {e}")
+            return -512
     
     return -512
 
diff --git a/src/modules/Rel4HVI4/readme.md b/src/modules/Rel4HVI4/readme.md
new file mode 100644
index 0000000..91308ad
--- /dev/null
+++ b/src/modules/Rel4HVI4/readme.md
@@ -0,0 +1 @@
+Card: Four Relays four HV Inputs 8-Layer Stackable HAT for Raspberry Pi - https://sequentmicrosystems.com/collections/industrial-automation/products/four-relays-four-inputs-for-raspberry-pi
\ No newline at end of file
diff --git a/src/modules/Rel4HVI4/router.py b/src/modules/Rel4HVI4/router.py
new file mode 100644
index 0000000..2ed2822
--- /dev/null
+++ b/src/modules/Rel4HVI4/router.py
@@ -0,0 +1,48 @@
+from fastapi import APIRouter
+import src.modules.Rel4HVI4.service as service
+from typing import Dict
+
+
+
+router = APIRouter(prefix="/rel4hvi4", tags=["Modules --> Rel4HVI4"])
+
+
+
+@router.post("/relay/all/{state}", description="Set all relays to required state (1/0)")
+def post_relay_all(state: bool):
+    service.set_relay_all(value=state)
+
+@router.post("/relay/{stack}/{state}", description="Set all relays on specified card to required state (1/0)")
+def post_relay_stack(stack: int, state: bool):
+    service.set_relay_stack(stack=stack, value=state)
+
+@router.post("/relay/{stack}/{channel}/{state}", description="Set all relays on specified card to required state (1/0)")
+def post_relay_stack(stack: int, channel, state: bool):
+    service.set_relay(stack=stack, relay=channel, value=state)
+
+
+@router.get("/relay/all", description="Get state of all relays", response_model=Dict[int, Dict[int, bool]])
+def get_relay_all():
+    return service.read_relay_all()
+
+@router.get("/relay/{stack}", description="Get all relays state of specified card", response_model=Dict[int, bool])
+def get_relay_stack(stack: int):
+    return service.read_relay_stack(stack=stack)
+
+@router.get("/relay/{stack}/{channel}", description="Get state of selected relay", response_model=bool)
+def get_relay(stack: int, channel: int):
+    return service.read_relay(stack=stack, relay=channel)
+
+
+
+@router.get("/opto/all", description="Get input state of all opto inputs", response_model=Dict[int, Dict[int, bool]])
+def get_opto_all():
+    return service.read_opto_all()
+
+@router.get("/opto/{stack}", description="Get input state all opto inputs on selected card", response_model=Dict[int, bool])
+def get_opto_stack(stack: int):
+    return service.read_opto_stack(stack=stack)
+
+@router.get("/opto/{stack}/{channel}", description="Get state of selected input", response_model=bool)
+def get_opto(stack: int, channel: int):
+    return service.read_opto(stack=stack, opto=channel)
\ No newline at end of file
diff --git a/src/modules/Rel4HVI4/service.py b/src/modules/Rel4HVI4/service.py
new file mode 100644
index 0000000..4f61e62
--- /dev/null
+++ b/src/modules/Rel4HVI4/service.py
@@ -0,0 +1,86 @@
+import lib4relind, os
+from typing import Dict
+
+
+stacks = [int(h) for h in os.getenv("MODULE_REL4HVI4_LEVELS", "")]
+if not stacks:
+    print("MODULE_Rel4HVI4_LEVELS is not set or invalid")
+
+for i in stacks:
+    print(f"Configured Rel4HVI4 card: {i}")
+
+
+def set_relay(stack: int, relay: int, value: bool):
+    """
+    Set specified relay to requested state
+    """
+    if stack in stacks and 1 <= relay <= 4:
+        lib4relind.set_relay(stack=stack, relay=relay, value=int(value))
+
+def set_relay_stack(stack: int, value: bool):
+    """
+    Set all relays to requested state on specified stack/card
+    """
+    (set_relay(stack=stack, relay=ch, value=value) for ch in range(1, 5))
+
+def set_relay_all(value: bool):
+    """
+    Set all relays to requested state
+    """
+    (set_relay_stack(stack=stack, value=value) for stack in stacks)
+
+
+def read_relay(stack: int, relay: int):
+    """
+    Read specified relay state
+    """
+    if stack in stacks and 1 <= relay <= 4:
+        try:
+            if lib4relind.get_relay(stack=stack, relay=relay) == 1:
+                return True
+            else:
+                return False
+        except:
+            return False
+    return False
+
+def read_relay_stack(stack: int):
+    """
+    Read all relays state on specified stack/card
+    """
+    return {relay: read_relay(stack=stack, relay=relay) for relay in range(1, 5)}
+
+def read_relay_all():
+    """
+    Read all relays state
+    """
+    return {stack: read_relay_stack(stack=stack) for stack in stacks}
+
+
+
+def read_opto(stack: int, opto: int):
+    """
+    Read specified opto input state
+    """
+    if stack in stacks and 1 <= opto <= 4:
+        try:
+            if lib4relind.get_opto(stack=stack, channel=opto) == 1:
+                return True
+            else:
+                return False
+        except:
+            return False
+    return False
+
+def read_opto_stack(stack: int):
+    """
+    Read all opto inputs state on specified stack/card 
+    """
+    return {opto: read_opto(stack=stack, opto=opto) for opto in range(1, 5)}
+
+def read_opto_all():
+    """
+    Read all opto inputs state
+    """
+    return {stack: read_opto_stack(stack=stack) for stack in stacks}
+
diff --git a/src/modules/router.py b/src/modules/router.py
index 83a6ad6..e14577a 100644
--- a/src/modules/router.py
+++ b/src/modules/router.py
@@ -1,6 +1,7 @@
 from fastapi import APIRouter
 
 from src.modules.RTD8.router import router as RTD8Router
+from src.modules.Rel4HVI4.router import router as Rel4HVI4Router
 
 
 
@@ -8,4 +9,5 @@ from src.modules.RTD8.router import router as RTD8Router
 
 router = APIRouter(prefix="/modules")
 
-router.include_router(router=RTD8Router)
\ No newline at end of file
+router.include_router(router=RTD8Router)
+router.include_router(router=Rel4HVI4Router)
\ No newline at end of file