Summary of "Embedded Systems and Design & Development - Feb 19, 2026 | Morning | VisionAstraa EV Academy"

Summary — Embedded systems design for a Battery Thermal Management System (BTMS)

Session: VisionAstraa EV Academy — Feb 19, 2026 (morning)

Maintain battery-cell temperature in the operational “Goldilocks” range: 15°C to 35°C.
If battery temperature > 80°C, isolate the battery from charger/load to prevent thermal runaway.
If ambient/pack temperature < 5°C on cold start, enable a heater until the pack reaches ~15°C before operation.

Temperature sensing (NTC thermistor) → ADC on microcontroller → control logic (MCU) → actuator(s).
Actuators:
- Compressor motor (circulant coolant) controlled via power electronics using PWM.
- Heater and isolation relays for protective actions triggered by temperature thresholds.
Cooling approach: active convection by circulating coolant (compressor speed controls coolant flow rate).

Sensor
- NTC thermistor mounted near the hottest spot (center of pack) to design for worst-case temperature.
- Signal conditioning (filtering, voltage scaling) recommended between thermistor and ADC.
MCU
- Arduino Uno / ATmega328 (ADC: 10-bit resolution).
- ADC: 10 bits → 0–1023 counts. Typical counts-per-volt: ~204.6 counts/V (0–1023 over 0–5 V).
- Example ADC pin in demo: A3.
- PWM pins available: six on UNO; example PWM used: digital pin 3.
- Serial debug: baud 9600.
Motor & power electronics
- DC motor used in simulation to represent coolant compressor (simplified).
- N-channel MOSFET as a low-side switch (gate ← PWM from MCU; drain ← motor; source ← ground).
- Freewheeling (flyback) diode placed antiparallel across the motor for inductive protection.
- Motor power supply separate from MCU supply (demo used a 9 V battery).
- PWM technique: control motor speed by duty-cycle modulation; Arduino analogWrite range 0–255 maps to 0–100% duty.
Topology notes
- Keep motor power separate from MCU supply where applicable.
- Include signal filtering to avoid noisy ADC readings.

Temperature-to-actuation mapping (example mapping used in session):
- ≤ 15°C → no coolant circulation (motor off).
- ≈ 20°C → small coolant flow (~20% motor speed).
- ≈ 25°C → moderate flow (~50%).
- ≥ 35°C → full speed (100% duty).
Protective logic
- If temperature > 80°C → open isolation relays (cut charge/discharge).
- If temperature < 5°C on startup → enable heater until pack reaches ≈ 15°C.
Sensor characterization and conversion
- Plot temperature (x) vs sensor voltage (y) and fit a linear relation y = m·x + c; invert to compute temperature from measured voltage.
- Map ADC counts → voltage → temperature:
  - ADC_count → voltage using counts-per-volt → temperature via inverted linear equation.
Integrated control loop (conceptual)
- Read ADC → compute temperature → determine PWM duty (or heater/isolation actions) → write PWM (0–255) to MOSFET → motor/compressor speed changes.

Tools shown: Tinkercad (circuit simulation & component slider), Serial Monitor, simulated multimeter.

Typical steps demonstrated:

Place MCU and temperature sensor in Tinkercad; wire VCC/GND/analog output to ADC pin.
Write basic Arduino code: configure pins, initialize Serial at 9600, use analogRead(A3), Serial.print raw ADC values.
Characterize sensor extremes with the Tinkercad slider and record voltages/ADC counts (examples given below).
Add motor, MOSFET, freewheeling diode and separate power source; connect MOSFET gate to PWM pin.
Implement PWM control with analogWrite(pin, value) where value ∈ [0,255] maps to duty cycle ∈ [0%,100%].
Test motor speed changes during simulation; debug with serial output and multimeter.
Combine sensor reading and PWM mapping into the final control loop (read ADC → convert to temperature → choose duty → analogWrite).

Place temperature sensors at the worst-case/hottest location (center of pack).
Always include a flyback/freewheeling diode across inductive loads (motors) to protect MOSFETs.
Use datasheets and example code; experimentally characterize sensors if the datasheet is unavailable.
Debug incrementally: validate sensor reading first, motor control separately, then integrate (bottom-up testing).
Keep power supplies separate for motors and the MCU where applicable.
Use signal conditioning and filtering on ADC inputs to reduce noise.
Document mapping functions and thresholds; test edge cases thoroughly.

MCU ADC: 10-bit (0–1023).
Example sensor voltages observed in simulation:
- ≈ 0.1 V at -40°C
- ≈ 1.75 V at 125°C
Example linear fit form: y (voltage, V) = m·T(°C) + c. (Instructor worked through deriving m and c from sensor endpoints.)
- Example values used in the demo: m ≈ 0.01 V/°C and c ≈ 5 — verify against actual datasheet before use.
ADC to voltage scaling: ~204.6 counts per volt (0–1023 over 0–5 V).
PWM write range: 0 → 0% duty, 255 → 100% duty.
Serial baud used: 9600.

Example conversion sequence (conceptual)

ADC_count → voltage:
- voltage = ADC_count / (counts_per_volt)
voltage → temperature:
- temperature = (voltage - c) / m
temperature → PWM duty:
- map temperature to a 0–255 analogWrite value according to the chosen temperature-to-actuation mapping.

(Verify m and c against the actual thermistor datasheet or by experimental characterization.)

Recommended workflow: follow system-level spec → decompose into subtasks → assign → implement and test subtasks → integrate.
Bottom-up testing and incremental validation emphasized.
This session is part of a knowledge-transfer series; upcoming topics include battery charging methods (CC, CV, float voltage, etc.).