Flip divider resistance circuit for thermistors (#90)

* updates

* remove sleep time

* fix imports

* move conversion

* chk

* Fix compilation error

* update -- tested

* remove full scale, etc

---------

Co-authored-by: Sam Der <[email protected]>

Author: ryescholin

pod-operation/src/components/lim_temperature.rs

@@ -12,15 +12,14 @@ const C_TO_K_CONVERSION: f32 = 273.15;
 // connected to a thermistor, with the ADS1015 is measuring the node connecting
 // the two (a voltage divider circuit).
 
-const DIVIDER_RESISTANCE: f32 = 22000.0; // Ohms
+const DIVIDER_RESISTANCE: f32 = 1000.0; // Ohms
 const V_IN: f32 = 5.0; // Volts
 const BETA: f32 = 3950.0; // Kelvins
 const R_0: f32 = 10000.0; // Ohms
 const ROOM_TEMP: f32 = 25.0 + C_TO_K_CONVERSION; // Kelvins
 
-fn voltage_to_temp(voltage: i16) -> f32 {
-	let voltage = f32::from(voltage) / 1000.0;
-	let thermistor_resistance = (voltage * DIVIDER_RESISTANCE) / (V_IN - voltage);
+fn voltage_to_temp(voltage: f32) -> f32 {
+	let thermistor_resistance = ((V_IN - voltage) * DIVIDER_RESISTANCE) / voltage;
 	let r_inf = R_0 * std::f32::consts::E.powf(-BETA / ROOM_TEMP);
 	let temp_kelvins = BETA / (thermistor_resistance / r_inf).ln();
 	temp_kelvins - C_TO_K_CONVERSION
@@ -43,7 +42,7 @@ impl LimTemperature {
 
 	pub fn read_lim_temps(&mut self) -> [f32; 4] {
 		[SingleA0, SingleA1, SingleA2, SingleA3]
-			.map(|channel| block!(self.ads1015.read(channel)).unwrap())
+			.map(|channel| f32::from(block!(self.ads1015.read(channel)).unwrap()) / 1000.0)
 			.map(voltage_to_temp)
 	}
 }