Gobinath Kannan
Embedded Software

EV instrument cluster: from prototype to series production

E-Works Mobility converted diesel commercial vehicles to electric drive. I was the sole firmware owner of the instrument cluster. I rebuilt the OEM's complete cluster alone by reverse-engineering its hardware and software (the OEM had a full team for it), added new functions, integrated it into our vehicle and took it to production in about 70–80 vehicles.

• Platform: STM32H7 with FreeRTOS, 480×800 RGB TFT with a TouchGFX GUI in C++ and SDRAM framebuffer, graphics, fonts and audio in external QSPI flash, SAI audio codec, stepper-motor gauges, LED chains, ADAS and safety warnings.
• CAN: communication with every ECU in the vehicle, data from the VCU and BMS, commands exchanged with the VCU. I decoded the OEM's CAN messages and defined the CAN interfaces between the cluster, the junction box and the telematics unit.
• Hardware: selected the MCU, flash, LCD and LED drivers, supplied the hardware requirements for schematic and PCB, reviewed schematics, brought up the boards and debugged at signal level with oscilloscope and logic analyzer.
• Testing: built an automated hardware-in-the-loop bench test with PCAN-Explorer: recorded vehicle CAN traffic replayed against the real hardware, with pass/fail reports, as part of the release validation.

CAN bootloader and over-the-air updates for the fleet

  boot.c  (simplified idea)
void boot_main(void)
{
    const app_hdr_t *hdr = APP_HEADER;

    /* new image waiting? flash it over ISO-TP */
    if (update_pending()) {
        receive_image_over_can();
    }

    /* check the image on every boot */
    if (crc32(hdr->start, hdr->len) != hdr->crc) {
        enter_recovery();  /* interrupted update */
    }

    jump_to_app(hdr->start);
}

Vehicle dataloggers and an Android diagnostic app over Bluetooth

BLE 5.0 mesh stack for Autoliv

Wireless traffic signal control for the Tamil Nadu Police

Growthboxes: remote-controlled growing boxes on ThingsBoard

Industrial dataloggers: many machines, one central receiver

PCB design: my own boards in KiCad

I design my own boards in KiCad, including 4-layer prototypes, and order them myself. The impedance measurement board (AD5933 with STM32) came out of the preparation phase of my master's thesis. The 32-channel force sensor system was my M.Sc. research project (grade 1.3): I designed the PCB, wrote the ESP32 firmware and tested the system.

Digital Stopwatch and Timer using FPGA

A digital stopwatch and countdown timer in synthesizable VHDL on a Xilinx Artix-7, running on the lab platform with push buttons and a character LCD. A start menu on the LCD selects the stopwatch or the timer.

• Control: FSM-based control with input debouncing and lap-time storage.
• Display: parallel driver for a 20×4 ST7036 character LCD.
• Top level: an arbiter between the stopwatch and the timer function.
• Verification: my own ModelSim testbenches and post-synthesis simulation in Vivado.

  stopwatch.vhd  (simplified idea)
type state_t is (IDLE, RUNNING, PAUSED);
signal state : state_t := IDLE;

process (clk)
begin
  if rising_edge(clk) then
    case state is
      when IDLE =>
        if btn_start = '1' then
          state <= RUNNING;
        end if;
      when RUNNING =>
        if tick_10ms = '1' then
          time_cnt <= time_cnt + 1;
        end if;
        if btn_lap = '1' then  -- store lap
          lap_mem(lap_idx) <= time_cnt;
        end if;
        if btn_stop = '1' then
          state <= PAUSED;
        end if;
      when PAUSED =>
        if btn_start = '1' then
          state <= RUNNING;
        end if;
    end case;
  end if;
end process;

Comparative Study of Excitation Signals for Bioimpedance Measurement on STM32 Microcontrollers: Performance and Energy Efficiency Analysis

Application: portable, battery-powered bioimpedance spectroscopy devices, which measure how biological tissue reacts to a small AC signal over many frequencies. Such a device needs the right microcontroller and the right excitation signal to get both accurate measurements and low power consumption.

My thesis compares nine excitation signals (multisine, DIBS, MLBS, linear, logarithmic and quadratic chirp, sine sweep) on six STM32 microcontrollers (F303, L476, L4P5, L552, U5A5, G474), each with DAC-based and timer-based generation, measured with the I-V method and FFT from 1 to 250 kHz.

• Signal generation: frequencies log-spaced and aligned to the FFT bins, quantized to 12 bit in MATLAB and exported as C arrays. On the STM32 the table streams via DMA into the DAC, triggered by a timer at 2 MHz. Binary signals (DIBS, MLBS) also run without a DAC: DMA writes the timer's compare register and the PWM output on a GPIO carries the signal.
• Acquisition: voltage and current captured with ADC1 and ADC2, timer-triggered, via DMA; impedance by FFT.
• Verification: every signal checked on the PicoScope in time domain and spectrum against the MATLAB simulation, including the effect of the internal RC clock (HSI) against the external crystal (HSE).
• Power and runtime: current measured with a Nordic Power Profiler Kit II and an ST-LINK-V3PWR (both agree within 0.1 mA); runtime with the ARM DWT cycle counter.
• Accuracy: validated against an HP4294A precision impedance analyzer on three test loads, including a Cole circuit as a tissue model; results exported over UART to CSV.

// key results

• Most accurate: on the Cole circuit, multisine had the lowest magnitude deviation (0.89 %) and DIBS-DAC the lowest phase deviation (0.42°). DAC-based signals beat their timer-based versions.
• Power: the signal type hardly matters; the MCU architecture does.
• Runtime: the Cortex-M33 parts (L5, U5) are fastest, about 40 ms for 20 frequencies. Sine sweep is about 3× slower.
• Limits found: MLBS works with the DAC but fails with the timer (GPIO too slow for the fast switching); sine sweep loses about 5 % to DAC settling.
• Recommendation: STM32L5 with multisine or DIBS-DAC for battery-powered devices, STM32U5 for a balance of low power and speed, STM32G4 for high accuracy thanks to its math accelerators (CORDIC, FMAC) and high-resolution timer.