Sensor Module

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{{wikibox title="Sensor Module" image="https://wiki.alignracing.no/bin/download/Electrical/Sensor%20Module/WebHome/ASM_AR26.png?rev=1.1" caption="3D model of the Sensor Module from Altium Designer" width="30" labelWidth="50"}}

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Voltage = 4.5V - 40V

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Fuse Current = 125mA

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Sensor Inputs = 13

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Voltage divider Inputs = 2

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3V3 Thermistor Inputs = 7

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5V Pressure Inputs = 4

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Communication Protocol = CAN FD

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Max Data rate = 1 Mbps

= Table of Contents =

= 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>>https://www.te.com/en/product-2311770-1.html]] which is directly solderen onto the circuit board. The plug needed for this system is the [[204517-3>>doc:Sandbox.TestPage3]], which uses crimps instead of solder cups which is common for the dsub connectors

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[[image:AR26_ASM pinout.png||height="287" width="616"]]

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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.

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(% style="width:1058.6px" %)

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|=(% style="width: 71px;" %)Pin Number|=(% style="width: 164px;" %)Pin Name|=(% style="width: 124px;" %)Type|=(% style="width: 70px;" %)(((

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Number

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)))|=(% style="width: 218px;" %)Pin name|=(% style="width: 58px;" %)(((

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Type

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)))|=(% style="width: 32px;" %)Pin Number|=(% style="width: 192px;" %)Pin Name|=(% style="width: 90px;" %)Pin Type

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|(% style="width:71px" %)(((

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3V3

)))|(% style="width:32px" %)33|(% style="width:192px" %) |(% style="width:90px" %)

Cooling Sensor 3

)))|(% style="width:58px" %)GND|(% style="width:32px" %)38|(% style="width:192px" %) |(% style="width:90px" %)

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Cooling Sensor 3

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)))|(% style="width:58px" %)3V3|(% style="width:32px" %)39|(% style="width:192px" %) |(% style="width:90px" %)

Cooling Sensor 1

)))|(% style="width:58px" %)3V3|(% style="width:32px" %)43|(% style="width:192px" %)Main Power|(% style="width:90px" %)GND

== Air Temperature Sensor ==

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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.

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[[image:circuit with marks.png||height="237" width="566"]]

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(% class="wikigeneratedid" %)

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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.

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(((

$$

R_T = R_f \frac{V_{out}}{V_{in} - V_{out}}

$$

)))

Where:

* {{mathjax}}$R_f${{/mathjax}} = The upper resistor in the voltage divider which stays fixed, which in this case is 4.7k {{mathjax}}$\Omega${{/mathjax}}

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* {{mathjax}}$V_{out}${{/mathjax}} = The voltage over the thermistor, and the voltage that the microcontroller will measure.

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* {{mathjax}}$V_{in}${{/mathjax}} = The supply voltage of the voltage divider, which in this case is a constant 3.3 {{mathjax}}$V${{/mathjax}}

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* {{mathjax}}$R_T${{/mathjax}} = Resistance of the thermistor

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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.

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(((

$$

T = \frac{1}{\frac{1}{T_0} + \frac{1}{\beta} \ln\left(\frac{R_T}{R_0}\right)}

$$

)))

where:

* {{mathjax}}$\beta${{/mathjax}} = 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.**//

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* {{mathjax}}$T_0${{/mathjax}} = The test temperature at which the thermistor is 10k {{mathjax}}$\Omega${{/mathjax}}, which in this case is 25 degrees celsius.

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* {{mathjax}}$R_0${{/mathjax}} = The resistance of the thermistor when it is 25 degrees celsius.

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* {{mathjax}}$R_T${{/mathjax}} = The current resistance of the thermistor.

=== Filtering ===

Considering that the sensor can only promise a reaction time of 5 seconds when in water, it can be assumed that a heavy filter will not add any problematic latencies. To ensure a low cost, the filter uses common components which will filter any noise above the inverter switching noise.

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(% style="font-size: 1.5em;" %)

(((

$$

F_c = \frac{1}{2 \pi R C}

$$

)))

Where:

* {{mathjax}}$F_c${{/mathjax}} = Cut-off frequency of the filter. Any noise with a frequency above this will be filtered out.

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* {{mathjax}}$R${{/mathjax}} = Resistance of the resistor in low-pass filter.

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* {{mathjax}}$C${{/mathjax}} = Capacitance of the capacitor in the low-pass filter.

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Using a resistor with 1k {{mathjax}}$\Omega${{/mathjax}} and a capacitor with 100 **nF **in capacitance, the cut-off frequency will be 1592 **Hz.**

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== Suspension Displacement Sensor ==

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For AR26, the same sensors from AR25 is reused. These are the [[Texense RSL-A-50-P>>https://cdn.shopify.com/s/files/1/0368/1989/files/technical_datasheet_RSL.pdf?413]] which can be connected as the entire voltage divider when using each end as supply and ground. The output of the sensor will then be the throw of the potentiometer.

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[[image:Suspension Displacement Circuit.png]]

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The sensor has a measurable range of 50mm with electrical range of 51mm, meaning that the electrical range will in practice be 1960 {{mathjax}}$\Omega${{/mathjax}} with 40 {{mathjax}}$\Omega${{/mathjax}} in total on each end.

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[[image:Actual Representation of Linear Potmeter.png||height="195" width="309"]]

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This can then be used to create the length of the sensor based on the input voltage.

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(% style="font-size: 1.5em;" %)

(((

$$

x = \frac{50}{1960} \left( \frac{2000\,V_{\text{out}}}{V_s} - 20 \right)

$$

)))

where:

* {{mathjax}}$x${{/mathjax}} = The mechanical placement excluding the dead length (178mm).

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* {{mathjax}}$V_s${{/mathjax}} = The supply voltage of the linear potentiometer, in this case it is 3.3 {{mathjax}}$V${{/mathjax}}.

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* {{mathjax}}$V_{out}${{/mathjax}} = The output voltage of the linear potentiometer. ranging from 0.033{{mathjax}}$V${{/mathjax}} to 3.267{{mathjax}}$V${{/mathjax}}.

=== Filtering ===

The sensors output latency can be expected to be a lot shorter than the air temperature sensor as the sensor is just a variable sensor based on placement. The limiting factor for the system which uses this information is the CAN-BUS messages from the inverters which send the information each 6.25 milliseconds. This means that the cut-off frequency cannot be any lower than 160 Hz, which will make the same type of low pass filter from the air temperature sensor acceptable with a cut-off frequency of 1591 Hz.

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== Gearbox Temperature Sensor ==

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The gearbox Temperature Sensor for AR26 will be the [[GAG10K3976B1>>https://www.te.com/en/product-GAG10K3976B1.html]], a NTC temperature probe which will be installed into a generic M5 bolt which is mounted on the upright in the wheel assembly. The thermistor will be connected in a voltage divider configuration where the thermistor is in the lower position so that the voltage lowers when the temperature increases.

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Wiki source code of Sensor Module