diff --git a/growpi.toml b/growpi.toml
new file mode 100644
index 0000000..1c267ba
--- /dev/null
+++ b/growpi.toml
@@ -0,0 +1,21 @@
+[board_settings]
+logic_level = 3.3
+
+[relay_settings]
+light_pin = 0
+fan_pin = 1
+water_pump_pin = 2
+relay_gpio_pins = [17, 27, 22, -1]
+
+[soil_moisture_settings]
+pin = 1
+voltage_100 = 1.417
+voltage_nominal = 2.823
+moisture_nominal = 0.41
+
+[thermistor_settings]
+pin = 0
+voltage_divider_resistance = 9700.0
+nominal_resistance = 10000.0
+nominal_temperature = 298.15
+thermal_constant = 3950.0
diff --git a/src/cli_mode.rs b/src/cli_mode.rs
index 3bb9d73..47255c6 100644
--- a/src/cli_mode.rs
+++ b/src/cli_mode.rs
@@ -160,7 +160,10 @@ fn init_state(config: &Configuration) -> GenericResult<ProgramState> {
 
 pub fn run_cli() {
     let mut rl = init_readline().unwrap();
-    let config = Configuration::default();
+
+    let config =
+        Configuration::from_file(std::path::Path::new("./growpi.toml")).unwrap_or_default();
+
     let mut program_state = init_state(&config).unwrap();
 
     'cli_loop: loop {
diff --git a/src/config.rs b/src/config.rs
index 9821b54..f5853f3 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -7,7 +7,7 @@ pub struct RelaySettings {
     pub light_pin: u8,
     pub fan_pin: u8,
     pub water_pump_pin: u8,
-    pub relay_gpio_pins: Vec<Option<u8>>,
+    pub relay_gpio_pins: Vec<i16>,
 }
 
 #[derive(Serialize, Deserialize)]
@@ -41,22 +41,18 @@ pub struct Configuration {
 }
 
 impl Configuration {
-    fn from_file(path: &std::path::Path) -> GenericResult<Configuration> {
+    pub fn from_file(path: &std::path::Path) -> GenericResult<Configuration> {
         let text = std::fs::read_to_string(path)?;
-        let config: Configuration = toml::from_str(text.as_str())?;
+        let config = toml::from_str(text.as_str())?;
         Ok(config)
     }
-    fn save_to_file(path: &std::path::Path, config: &Configuration) -> GenericResult<()> {
-        let text = toml::to_string_pretty(config)?;
+    pub fn save_to_file(&self, path: &std::path::Path) -> GenericResult<()> {
+        let text = toml::to_string_pretty(self)?;
         std::fs::write(path, text)?;
         Ok(())
     }
 }
 
-const THERMISTOR_NOMINAL_RESISTANCE: f32 = 10_000.;
-const THERMISTOR_NOMINAL_TEMPERATURE: f32 = 298.15;
-const THERMISTOR_CONSTANT: f32 = 3950.;
-
 impl Default for Configuration {
     fn default() -> Self {
         Self {
@@ -65,7 +61,7 @@ impl Default for Configuration {
                 light_pin: 0,
                 fan_pin: 1,
                 water_pump_pin: 2,
-                relay_gpio_pins: [Some(17), Some(27), Some(22), None].to_vec(),
+                relay_gpio_pins: [17, 27, 22, -1].to_vec(),
             },
             soil_moisture_settings: SoilMoistureSettings {
                 pin: 1,
@@ -83,3 +79,16 @@ impl Default for Configuration {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_write_default() {
+        let config = Configuration::default();
+        config
+            .save_to_file(std::path::Path::new("./growpi.toml"))
+            .unwrap();
+    }
+}
diff --git a/src/io.rs b/src/io.rs
index 73858af..482ec3e 100644
--- a/src/io.rs
+++ b/src/io.rs
@@ -39,7 +39,11 @@ impl Relay {
             .clone()
             .into_iter()
             .map(|pin| {
-                pin.and_then(|pin| {
+                match pin {
+                    -1 => None,
+                    _ => Some(pin as u8),
+                }
+                .and_then(|pin| {
                     let result = (|| -> GenericResult<OutputPin> {
                         Ok(Gpio::new()?.get(pin)?.into_output())
                     })();