Sensor Module
Description
The Sensor module is designed to measure any extra analog signals rear of the firewall. For AR26, the module is designed to measure two suspension displacement sensors, two oil temperature, four water pressure, four water temperature, and one air temperature sensor. All of the measurements are then transmitted to a CAN network, which there are two of.
Wiring Diagram
In the following section, how the sensor module is connected will be covered. The connector for the sensor module is a High-Density d'sub-44 which is directly solderen onto the circuit board. The plug needed for this system is the 204517-3, which uses crimps instead of solder cups which is common for the dsub connectors
In the figure above, the pinout shows how the pins are divided. Each box shows which pins belong together for each usecase, where the red box is the power input. Yellow boxes are for each canbus network, while the green box is for each sensor used in AR26.
| Pin Number | Pin Name | Type | Pin | Pin name | Type | Pin Number | Pin Name | Pin Type |
|---|---|---|---|---|---|---|---|---|
1 | Air Temperature | Analog (0-3.3V) | 16 | Air Temperature | GND | 31 | Suspension Displacement Left | GND |
| 2 | Suspension Displacement Left | Analog (0-3.3V) | 17 | Suspension Displacement Left | 3V3 | 32 | Suspension Displacement Right | GND |
| 3 | Suspension Displacement Right | Analog (0-3.3V) | 18 | Suspension Displacement Right | 3V3 | 33 | ||
| 4 | Oil Temperature Right | Analog (0-3.3V) | 19 | Oil Temperature Right | 3V3 | 34 | ||
| 5 | Oil Temperature Left | Analog (0-3.3V) | 20 | Oil Temperature Left | 3V3 | 35 | ||
| 6 | Cooling Temperature 4 | Analog (0-3.3V) | 21 | Cooling Sensor 4 | GND | 36 | ||
| 7 | Cooling Pressure 4 | Analog (0-5V) | 22 | Cooling Sensor 4 | 3V3 | 37 | ||
| 8 | Cooling Temperature 3 | Analog (0-3.3V) | 23 | Cooling Sensor 3 | GND | 38 | ||
| 9 | Cooling Pressure 3 | Analog (0-5V) | 24 | Cooling Sensor 3 | 3V3 | 39 | ||
| 10 | Cooling Temperature 2 | Analog (0-3.3V) | 25 | Cooling Sensor 2 | GND | 40 | ||
| 11 | Cooling Pressure 2 | Analog (0-5V) | 26 | Cooling Sensor 2 | 3V3 | 41 | ||
| 12 | Cooling Temperature 1 | Analog (0-3.3V) | 27 | Cooling Sensor 1 | GND | 42 | ||
| 13 | Cooling Pressure 1 | Analog (0-5V) | 28 | Cooling Sensor 1 | 3V3 | 43 | Main Power | GND |
| 14 | CAN High 1 | CAN | 29 | CAN Low 2 | CAN | 44 | Main Power | +24V |
| 15 | CAN Low 1 | CAN | 30 | CAN High 2 | CAN |
Typical Application
This section will cover the sensors which will be used for AR26 and how the sensor module is designed to accommodate them.
Air Temperature Sensor
The air temperature sensor will be used to have a dynamic reference setpoint for the cooling system. This could reduce the current draw from the low voltage system compared to having a fixed reference point. This is because the regulator will not try to cool the water to a temperature lower than the ambient temperature. The sensor works as a resistor which varies depending on its temperature. Where in this case, the resistance lowers when the temperature increases (NTC). To make the microcontroller able to measure the changes in resistance, the thermistor is put into a voltage divider circuit.
As shown in the figure above, the thermistor is put into a voltage divider circuit with a 4k7 ohm resistor to convert the resistance changes of the thermistor to a measurable voltage. To find the temperature of the thermistor based on the voltage measure by the analog-to-digital converter (ADC), the resistance of the thermistor needs to be calculated based on the voltage from a voltage divider.
Where:
- \(R_f\) = The upper resistor in the voltage divider which stays fixed, which in this case is 4.7k \(\Omega\)
- \(V_{out}\) = The voltage over the thermistor, and the voltage that the microcontroller will measure.
- \(V_{in}\) = The supply voltage of the voltage divider, which in this case is a constant 3.3 \(V\)
- \(R_T\) = Resistance of the thermistor
Knowing this, the resistance of the thermistor can be added into the following equation. This will determine the temperature of the thermistor based on the known resistance and the beta value of the thermistor.
- \(\beta\) = material constant that defines the steepness of its resistance-temperature curve between two temperature points, usually 25/85 degrees celsius. In this case it is 3694 K
- \(T_0\) = the test temperature at which the thermistor is 10k \(\Omega)\