Embedded Systems and Design & Development - Feb 18, 2026 | Afternoon | VisionAstraa EV Academy

Current Sensors in Electric Vehicles

Recap of Previous Discussions

• The session begins with a recap of the previous day's discussions on current sensors suitable for electric vehicle (EV) environments.

• Various types of current sensors were reviewed, including shunt resistors, Hall effect-based sensors, current transformers, flux gate sensors, and magnetoresistive sensors.

Types of Current Sensors

• Shunt resistor-based sensors create a voltage drop by being placed in series with the load to measure current flow; they are cost-effective and simple.

• Hall effect and shunt resistors can measure both AC and DC currents, while current transformer-based sensors are limited to AC measurements only due to their design.

Design Considerations for Current Measurement

• Discussion on design calculations necessary when implementing shunt resistors for measuring current in various loads such as EV motors or battery charging systems.

• Example scenario: assessing a maximum load of 1 ampere using a generic 10V source connected to a variable resistance load ranging from 10 ohms to 100 ohms.

Understanding Ohm's Law in Context

• The relationship between voltage (V), current (I), and resistance (R) is highlighted through Ohm's law; variations in resistance affect the current supplied by the source.

• As resistance increases from 10 ohms to 100 ohms, the resulting current decreases from 1 ampere to 0.1 ampere.

ADC Compatibility and Voltage Conversion

• Embedded controllers require knowledge of the flowing current for protective measures; however, they can only measure voltage variations via Analog-to-Digital Converters (ADCs).

• To convert current into measurable voltage, a sense resistor is inserted into the circuit. The voltage drop across this resistor indicates the amount of current flowing through it based on Ohm's law.

Selecting Sense Resistor Values

• When selecting a sense resistor value, it’s crucial that the maximum voltage drop does not exceed ADC limits—specifically ensuring that at maximum expected current (1A), the drop remains within acceptable levels.

• The goal is to ensure that at peak conditions, the sense resistor generates no more than 5 volts across it for compatibility with standard ADC inputs.

Understanding Current Sensing Resistors

Maximum Voltage and Current Specifications

• The maximum voltage required is 5 volts, with a maximum current of 1 ampere flowing through the resistance. This results in a calculated drop of 5 ohms.

Selection of Resistor Value

• A 5-ohm resistor is initially considered for use, but there are reasons to explore alternatives that will be discussed later.

Importance of Electrical Connections

• When supplying voltage to the ADC terminal, it must be referenced to ground; careful placement of the sensor resistor is crucial to avoid floating terminals.

Reference Potential for Accurate Measurements

• If the reference terminal does not have a potential of zero, it can lead to inaccurate ADC measurements. Proper installation ensures reliable readings from input terminals (A0 to A6).

Relationship Between Load Current and Voltage

• The ADC measures voltage variations, but the focus should be on correlating these variations with load current. Establishing this relationship is essential for control decisions regarding overcurrent conditions.

Mapping Current and Voltage Relationships

Inferring Load Current from ADC Output

• By determining how much current corresponds to specific voltage readings (e.g., 5 volts indicating 1 ampere), embedded controllers can make informed decisions based on ADC outputs.

Formulating Relationships for Control Decisions

• Understanding the correlation between current and voltage allows engineers to program microcontrollers effectively for protective actions.

Tabulation vs. Mapping Values

• Engineers can either tabulate or graphically map values to find relationships between current and voltage; mapping provides a visual representation that aids understanding.

Linear Relationship Assumption

• Assuming a linear relationship simplifies calculations; plotting current against voltage yields a straight line where slope (m) represents the change in output per unit change in input.

Determining Slope for Design Applications

• The slope (m) can be derived from any two points on the linear graph, allowing engineers to apply this knowledge across varying ranges of current (0 to 1 ampere).

Understanding Voltage and Current Relationships in Embedded Systems

Formulating the Characteristic Equation

• The relationship between voltage (y-axis) and current (x-axis) is established as y = 5x , where 5 represents the slope of the line.

• This equation allows for calculating one parameter if the other is known, facilitating control decisions in embedded systems.

Practical Application of the Equation

• When an ADC senses a voltage of 3 volts, it can be used to calculate current: x = 3/5 = 0.6 amperes.

• This method demonstrates how to derive load current from sensed voltage using the formulated characteristic equation.

Exploring Further Calculations

• If an ADC detects a voltage of 4 volts, applying the same relation yields a load current of x = 4/5 = 0.8 amperes, showcasing practical application in real-time scenarios.

• The process emphasizes understanding how to exploit data for control decisions within embedded systems.

Generalizing Measurement Techniques

• The discussed methodology applies not only to current but also to other parameters like temperature, emphasizing versatility in measurement techniques across different sensors and transducers.

• Previous discussions on conversion ratios for measuring high voltages illustrate foundational concepts necessary for accurate parameter measurement.

Importance of Relationship Formulation

• It’s crucial to remember how relationships are formulated; input parameters (voltage) lead to output parameters (current). This understanding is vital for programming embedded controllers effectively.

• By plotting these relationships, one can create tables that help visualize outputs corresponding to various inputs, enhancing clarity in decision-making processes within embedded systems.

Linear vs Non-linear Relationships

• The relationship between output voltage and input current is linear; however, many practical cases may exhibit non-linearity, particularly with temperature sensors which will be discussed later on.

• Recognizing this distinction helps in developing algorithms that accurately reflect real-world conditions when programming embedded systems.

Implementing Control Decisions

• Once characterized equations are established, they can be integrated into conditional statements within programs: e.g., "If current > 1 ampere then cut off supply." This highlights their role in automated control systems based on sensor feedback.

• Emphasizing formulation accuracy ensures effective decision-making capabilities within embedded applications by leveraging derived relationships correctly throughout programming efforts.

Understanding Amplifier Circuits and Their Importance

Introduction to Amplifier Circuits

• The discussion begins with a brief overview of amplifier circuits, specifically feedback amplifier circuits, which are essential for voltage amplification.

• A question arises regarding the relationship between input and output parameters in these circuits, setting the stage for deeper exploration into their necessity.

Power Consumption in Sense Resistors

• The speaker transitions to discussing power consumption in sense resistors when maximum current flows through them, emphasizing the need for calculations based on previous knowledge.

• The formula used for computing power loss is introduced: P = I^2 times R , where I is the current and R is resistance.

Calculating Power Loss

• With a maximum current of 1 ampere flowing through a 5-ohm resistor, the calculated power loss amounts to 5 watts.

• This significant power loss translates into heat dissipation within the resistor, necessitating specialized components that can handle such thermal stress.

Addressing Power Wastage

• The discussion highlights that half of the load's power (10 watts) is wasted across the sense resistor, presenting an unacceptable scenario that needs resolution.

• To mitigate this wastage, reducing voltage across sense resistors becomes crucial; lower resistance values lead to reduced current flow.

Impact on Measurement Accuracy

• A hypothetical scenario introduces a 0.1-ohm resistance value aimed at controlling power loss; however, it results in only 0.1 volts across the sensor resistor.

• This low voltage poses challenges for ADC accuracy since it operates within a range up to 5 volts, leading to potential measurement inaccuracies.

Need for Signal Amplification

• To counteract both power loss and measurement accuracy issues, signal amplification becomes necessary.

• Combining instrumentation amplifiers with magnitude amplifiers ensures that signals fed into ADC inputs maintain integrity without loading effects.

Conclusion on Sensor Design Considerations

• Manufacturers typically incorporate noise suppression mechanisms alongside amplification in IC packages or sensing boards as standard practice.

• Custom solutions require careful design considerations and testing before deployment but fall outside this particular discussion's scope.

Current Sensors and Control Logic

Understanding Current Sensors

• The discussion emphasizes the importance of establishing a relationship between the sensed parameter (current) and the ADC input voltage, which is crucial for effective control decisions.

• Formulating this relationship is highlighted as a critical step before making any control decisions regarding current sensors, particularly in applications like short circuit protection for batteries.

Practical Application with Battery Cells

• A lithium-ion battery cell is used as an example to illustrate how current sensors can be integrated into charging or discharging circuits.

• The placement of the current sensor is discussed, noting that it should be installed at an appropriate location within the circuit to ensure accurate readings.

LED Indicators for Current Levels

• An exercise is suggested where if the sensed current exceeds 1 ampere, a built-in LED should turn on; conversely, if it remains within safe levels, the LED will remain off.

• This logic serves to isolate the battery under overcurrent conditions, similar to previous discussions about isolating batteries during overvoltage situations.

Tips for Using Tinkercad

• Users are advised to utilize Tinkercad's help context when wiring components, especially when distinguishing between anode and cathode terminals of LEDs.

• It’s noted that confusion often arises regarding terminal connections; moving the mouse cursor over terminals provides descriptions that clarify their functions.

Debugging Circuit Connections

• When troubleshooting connections on an Arduino board, users are encouraged to verify connections by checking against known potential points (VCC and ground).

• If issues arise with circuit operation, it's recommended to create a new diagram for testing individual components before returning to modify existing configurations.

Processing ADC Values

• A brief overview of processing ADC values is provided; understanding how these values are stored in memory locations corresponding to ADC data is essential.

• The discussion explains how analog readings from sensors convert into digital data represented as integers in programming environments like Arduino.

Understanding ADC Voltage and Output Relationships

Key Concepts in ADC Measurement

• The importance of not directly inputting fixed voltages (like 3V or 2V) when experimenting with programs, as it may hinder understanding the relationship between input and output.

• Input voltage for the ADC is up to 5 volts, while the output corresponds to 1024 states (2^10), including zero. A slight error in representation (e.g., using 1023 instead of 1024) is acceptable.

• To find the relationship between input (x) and output (y), calculate the slope using delta y and delta x, similar to previous examples.

• The resolution of a measurement system is crucial; for a 10-bit ADC like ATmega328, this impacts accuracy significantly.

• Accuracy can be calculated as 1/2^textresolution bits ; for a 10-bit system, this results in approximately 1 millivolt resolution.

Practical Applications and Programming Considerations

• Emphasizes the need to apply these concepts when writing programs related to voltage measurements; suggests practicing on Tinkercad as homework.

• Upcoming sessions will cover various aspects of Battery Management Systems (BMS), focusing on control decisions based on monitored parameters.

Thermal Management in BMS

Importance of Temperature Monitoring

• Discussion will include algorithms for computing state of charge and health, which are essential for making protective control decisions during charging/discharging processes.

• Introduction to hardware-in-the-loop simulations that allow testing programs with minimal hardware setups while simulating inputs/outputs effectively.

Types of Temperature Sensors

• Overview of different sensors used for measuring voltage and current leads into temperature sensor types critical for BMS applications.

• Highlights the necessity of monitoring temperatures at key locations such as batteries and traction motors to ensure safety for both equipment and personnel.

Reviewing Temperature Sensor Types

Commonly Used Sensors

• Review includes conventional thermistors, RTDs (Resistance Temperature Detectors), semiconductor-based IC sensors, and non-contact types. Focuses on their applicability within automotive sectors.

Understanding Temperature Measurement Sensors

Overview of Temperature Measurement Techniques

• The sensor must contact the surface for temperature measurement; non-contact methods use infrared sensors that detect emitted infrared light to gauge temperature.

• Thermocouples are used for high-temperature measurements, while fiber optic sensors offer isolation and accuracy but are costly, limiting their use in regular automotive applications.

• Noise rejection capabilities make certain temperature sensors desirable, though their cost restricts them primarily to R&D tasks.

Discussion on Thermistors

• The term "thermistor" combines "thermal" and "resistor," indicating that its resistance varies with temperature changes.

• There are two types of thermistors: NTC (Negative Temperature Coefficient), where resistance decreases as temperature increases, and PTC (Positive Temperature Coefficient), where resistance increases with rising temperatures.

Characteristics and Challenges of Thermistors

• The relationship between resistance and temperature in PTC thermistors is non-linear, complicating characterization compared to linear relationships seen in other sensors.

• Non-linear characteristics pose challenges for creating equations to describe the relationship between input parameters (temperature) and output parameters (resistance).

Solutions for Characterizing Thermistor Behavior

• Curve fitting techniques can be employed to derive equations from non-linear data, although they can be computationally intensive.

• An alternative method involves using lookup tables that map input values (temperature) to output values (resistance), allowing microcontrollers to reference stored data efficiently.

Understanding Lookup Tables and Transducers in Embedded Control

Overview of Lookup Table Method

• The lookup table method is a straightforward approach requiring simple experimentation to collect data, which can then be tabulated for use in microcontrollers to assess resistance or temperature based on output parameters like voltage.

• This method is frequently utilized in developing embedded control programs, highlighting its importance in practical applications.

Distinction Between Sensors and Transducers

• A transducer differs from a sensor; while both measure physical parameters, sensors respond directly to stimuli, whereas transducers convert signals from one form to another (e.g., temperature to electrical voltage).

• The input parameter for transducers is typically non-electrical (like temperature), and the output is an electrical signal, emphasizing their role in measurement systems.

Characteristics of Thermistors

• Thermistors are a type of transducer that require energization; they contain thermistor elements whose resistance varies with temperature changes.

• When applying a fixed voltage (e.g., 5 volts), the current flowing through the thermistor will vary depending on its resistance, which changes with temperature fluctuations.

Electrical Signal Processing

• For PTAC thermistors, resistance increases with rising temperatures; conversely, NTAC thermistors exhibit an inverse relationship. Energizing these devices produces an output voltage corresponding to the input parameter.

• If the generated voltage is low (0 to 0.5 volts), amplification circuits may be necessary for accurate readings by ADC terminals.

Resistance Temperature Detectors (RTDs)

• RTDs operate similarly to thermistors by measuring temperature variations through changes in resistance. They can utilize different circuit configurations such as two-wire or four-wire connections for improved accuracy.

• Lead resistance can affect measurements when dealing with low-voltage drops from sensing elements; this emphasizes the need for careful consideration of wiring and connections.

Impact of Conductor Resistance

• Conductors theoretically should have no resistance but practically possess finite resistances that influence current flow and create measurable voltage drops affecting ADC readings.

• Lead resistance introduces errors into measurements, potentially corrupting actual data readings from RTDs or similar sensors and complicating accurate temperature assessments.

Understanding Lead Resistance in Temperature Measurement

Overcoming Lead Resistance

• The use of 3-wire and 4-wire methods helps assess lead resistance, allowing for accurate temperature measurements by subtracting known resistances (e.g., 0.1 ohm on each side).

• By accounting for lead resistance during calculations, engineers can improve the accuracy of temperature readings, effectively mitigating voltage drop issues caused by leads.

Importance of Datasheets

• Embedded programmers often rely on datasheets from manufacturers to gather necessary information about sensors and their specifications.

• Datasheets are crucial for both design engineers and embedded engineers to ensure reliable program development that responds accurately to sensor data.

IC-Based Sensors: Digital vs. Analog

Transition from Analog to Digital

• IC-based sensors are preferred when digital data is required instead of analog values; this transition allows for more efficient data processing.

• The LM35 sensor is a popular choice among hobbyists and some industrial applications, providing an analog voltage output corresponding to temperature changes.

Data Transmission Methods

• For digital communication with microcontrollers, IC-based solutions convert analog signals into digital formats using serial protocols like I2C.

• Serial transmission reduces the number of wires needed for communication, making it easier to connect multiple devices while maintaining efficiency.

Limitations and Applications of IC-Based Solutions

Acceptable Data Transfer Rates

• While serial data transfer rates are limited compared to parallel transfers, they are sufficient for temperature measurements since significant changes occur over longer periods (seconds or minutes).

Infrared Temperature Sensors

• Infrared sensors measure temperature without direct contact by detecting emitted infrared rays from heat sources; these sensors are typically more expensive than other types.

• Infrared sensors often come in arrays (e.g., Panasonic's AMG series), which consist of multiple diodes arranged in rows and columns for enhanced measurement capabilities.

Conclusion: Understanding Sensor Technologies

Summary of Key Sensor Types

• The discussion highlights various sensor technologies used in temperature measurement, emphasizing the importance of understanding their functionalities and applications within embedded systems.

Understanding Temperature Sensors in Automotive Applications

Overview of Thermographs and Temperature Sensors

• Thermographs provide temperature profiles over wide areas, but are not suitable for electric vehicle (EV) applications; contact-type temperature sensors are preferred.

• Data from temperature sensors is communicated using the I2C protocol, which includes serial data and clock terminals for digital transmission.

• Embedded systems engineers, especially in automotive fields, should be familiar with bus protocols like LIN, CAN, and I2C.

Application of Temperature Sensors

• The choice of temperature sensors depends on specific applications within EV systems, such as battery packs and onboard chargers.

• For battery pack temperature sensing, options include thermistors or RTDs; both types are acceptable for monitoring temperatures effectively.

Sensor Selection Criteria

• Commonly used sensors in automotive applications include thermistors and RTDs; IC-based sensors can also be advantageous when integrated into Battery Management Systems (BMS).

• Key factors influencing sensor selection include cost, stability, reliability, and accuracy.

Safety Standards Considerations

• When selecting sensors, compliance with safety standards (ISO standards discussed previously) is crucial to ensure they meet required safety levels.

• NTC thermistors are widely employed due to their cost-effectiveness; however, RTDs may be chosen for higher accuracy needs.

Characteristics Comparison of Sensors

• A comparison of characteristics between thermistors and RTDs helps inform decisions on sensor usage based on application requirements.

• NTC thermistors and RTDs are preferred due to their affordability and sensitivity; long-term stability is essential to avoid performance degradation over time.

Conclusion on Sensor Reliability

• Stability over time is critical; if a sensor's response characteristics degrade after prolonged use, it may necessitate algorithm adjustments to maintain system safety.

Temperature Measurement in Circuits

Overview of Temperature Measurement Circuit

• The circuit diagram illustrates how temperature measurements are conducted to gather pack temperature information using a thermistor mounted on the pack.

• The thermistor's readings are converted into voltage, which is then processed by an Analog-to-Digital Converter (ADC).

• It is noted that the relationship between the thermistors and temperature is non-linear, indicating complexity in data interpretation.

Implementation of Lookup Table Method

• A lookup table method is employed to interpret ADC values for determining temperature. This involves storing a table in program memory.

• The algorithm matches the ADC voltage value with corresponding entries in the lookup table to ascertain the current temperature.

Future Demonstrations and Applications

• Future sessions will include demonstrative algorithms for clarity on programming related to temperature measurement and control decisions.

• These algorithms can be applied not only for protection but also for maintaining cabin temperatures, showcasing versatility.

Understanding Voltage to Temperature Conversion

• Queries arise regarding how voltage values translate into precise temperature readings, paralleling methods used in current sensor applications discussed earlier.

• Characterizing the relationship between voltage and temperature is essential; once established, it allows accurate determination of temperature from ADC readings.

Utilizing Datasheets for Characteristic Curves

• Reference to datasheets (e.g., LM35) highlights their importance as they provide characteristic curves necessary for writing effective programs related to temperature measurement.

• Participants are encouraged to engage with practical exercises like Tinker CAD and bring up any doubts in future sessions.