1. IR Receiver Diode
   • Detect infrared signals and generate pulses.
2. Transistor (e.g., Q1)
   • For signal amplification and conditioning.
3. Microcontroller
   • Handles counting pulses and communication via I2C or SPI (e.g., an ESP32, Arduino, or any other MCUs with I2C/SPI capabilities).
4. I2C/SPI Interface
   • For communication with other devices.

1. IR Receiver Circuit:
   • Use the IR receiver diode to detect pulses and feed them into a counter on the microcontroller.
2. Amplification and Signal Conditioning:
   • Amplify and condition the pulses if necessary using a transistor.
3. Counter Implementation:
   • Use a microcontroller with a built-in hardware counter or timer module.
4. Communication Interface:
   • Implement I2C or SPI communication on the microcontroller to output the count value.

1. IR Receiver Diode Connection:
   • Connect the anode of the IR receiver diode to a suitable pull-up resistor and supply voltage.
   • Connect the cathode to ground.
   • Connect the pulse output of the IR receiver to the base of the transistor Q1.
2. Amplification using Transistor Q1:
   • Connect Q1:E to GND (Net: GND).
   • Connect a series resistor (if necessary) to the base of Q1.
   • Connect the collector of Q1 to a pull-up resistor and then to the microcontroller input pin.
3. Counter via Microcontroller:
   • Connect the output pulse from the IR receiver circuit (post-transistor) to a digital input pin on the microcontroller.
4. I2C/SPI Interface:
   • Connect the appropriate I2C/SPI pins on the microcontroller to your communication bus.

• Connect $R_1:1$ to $R_1:2$, $V_1:2$, and $R_2:1$.
• Connect $R_1:2$ to $Q_1:B$.
• Connect $Q_1:E$ to GND.
• Connect $Q_1:C$ to $D_1:K$.
• Connect $D_1:A$ to $R_2:P2$.

1. Select the Microcontroller:
   • Choose a microcontroller and confirm available GPIO pins and interfaces for I2C/SPI communication.
2. Update the Schematic:
   • Add the microcontroller and make the connections as described above including power lines.
3. Software Development:
   • Write code to count pulses and communicate via I2C or SPI.

1. MOSI (Master Out Slave In)
2. MISO (Master In Slave Out)
3. SCLK (Serial Clock)
4. CS (Chip Select)

• SPI Pins:
  • GPIO23: MOSI
  • GPIO19: MISO
  • GPIO18: SCLK
  • GPIO5: CS

• SPI Pins (Broadcom GPIO numbering):
  • GPIO10: MOSI (pin 19 on the header)
  • GPIO9: MISO (pin 21 on the header)
  • GPIO11: SCLK (pin 23 on the header)
  • GPIO8: CE0 (CS) (pin 24 on the header)

1. IR Receiver Diode to Transistor Q1:
   • Connect the IR receiver diode anode to a pull-up resistor connected to 3.3V (for ESP32) or 5V (for RPI4, though 3.3V is safer for GPIO pins).
   • Connect the IR receiver diode cathode to ground.
   • Connect the output pulse of the IR receiver diode to the base of Q1 through a current-limiting resistor.
2. Transistor Q1 Amplification:
   • Connect Q1:E to GND.
   • Connect the collector of Q1 to a pull-up resistor (connected to 3.3V) and then to a digital input pin of the microcontroller for pulse detection.
3. Connect SPI Pins to Microcontroller:
   • ESP32:
     • Connect MOSI from ESP32 (GPIO 23) to the SPI device if necessary.
     • Connect MISO from the device to ESP32 (GPIO 19).
     • Connect SCLK from ESP32 (GPIO 18) to the SPI device.
     • Connect the CS (Chip Select) from ESP32 (GPIO 5) to the SPI device.
   • Raspberry Pi 4:
     • Connect MOSI from RPI4 (GPIO 10) to the SPI device if necessary.
     • Connect MISO from the device to RPI4 (GPIO 9).
     • Connect SCLK from RPI4 (GPIO 11) to the SPI device.
     • Connect CE0 from RPI4 (GPIO 8) to the SPI device.

• Output from IR Receiver (after transistor) to Microcontroller:
  • Connect Q1:C (collector) to a pull-up resistor and then to a digital input pin on the ESP32 or Raspberry Pi 4. Let’s assume GPIO 14 for ESP32 or GPIO 17 for RPI4.

• Make sure the IR receiver output voltage levels are compatible with the GPIO pins of the microcontroller (3.3V for ESP32 and Raspberry Pi).
• Implement debounce logic in your software to accurately count pulses from the IR receiver.

1. Transistor Q1 Circuit:
   • Connect IR Receiver Diode Anode to 3.3V through a pull-up resistor.
   • Connect IR Receiver Diode Cathode to GND.
   • Connect IR Receiver output to Q1:B (with a current-limiting resistor).
2. Connections:
   • Connect IR Receiver (output) to Q1:B.
   • Connect Q1:E to GND.
   • Connect Q1:C to ESP32:G14 or RPI4:G17 with a pull-up resistor to 3.3V.
   • Connect ESP32 (or RPI4) SPI Pins accordingly:
     • ESP32:
       • Connect ESP32:G23 (MOSI), G19 (MISO), G18 (SCLK), G5 (CS) to the SPI device.
     • RPI4:
       • Connect RPI4:G10 (MOSI), G9 (MISO), G11 (SCLK), G8 (CS) to the SPI device.

1. Configure SPI in Slave Mode:
   • Set up your microcontroller to act as an SPI slave device. This will allow it to receive pulses as SPI data.
2. Generate a Clock for SPI:
   • Your IR pulses will act as the clock signal for the SPI. Each pulse will shift data into the SPI slave.
3. Capture Data on SPI:
   • Each pulse will trigger an SPI transaction that can be interpreted as a count increment.

1. SPI Clock (SCK):
   • Connect the output of your pulse circuit (transistor collector) to the SPI clock pin (SCK) of the microcontroller. This way, each pulse acts as an SPI clock pulse.
2. SPI Data (MOSI):
   • You can connect MOSI to a high/low signal to facilitate counting. This data isn’t necessarily useful here but is part of SPI protocol.
3. SPI Chip Select (CS):
   • Connect CS to a fixed state (GND or 3.3V) if not using an external device to initiate transactions.
4. SPI MISO:
   • This pin will not be needed for counting but should be properly terminated if not in use.

1. IR Receiver Circuit to Transistor Q1:
   • Connect IR receiver anode to a pull-up resistor and 3.3V.
   • Connect IR receiver cathode to GND.
   • Output of IR receiver goes to Q1:B via a current limiting resistor.
2. Transistor Q1:
   • Q1:E connects to GND.
   • Q1:C connects to the SPI clock pin (ESP32 GPIO 18 or RPI4 GPIO 11).
3. SPI Connections:
   • IR Receiver Pulse Output (after Q1) to SPI Clock Pin:
     • ESP32: Connect Q1:C to GPIO 18 (SCLK).
     • Raspberry Pi 4: Connect Q1:C to GPIO 11 (SCLK).
   • SPI MOSI to High/Low signal source:
     • ESP32: Connect GPIO 23 (MOSI) to a stable high (3.3V) or low (GND) signal.
     • Raspberry Pi 4: Connect GPIO 10 (MOSI) similarly.
   • CS Pin Configuration:
     • If not using external select, ground it or connect it to 3.3V.
       • ESP32: Set CS (e.g., GPIO 5) to a fixed state.
       • Raspberry Pi 4: Set CE0 (GPIO 8) to fixed state.

• IR Receiver to Q1:
  • Connect IR Receiver Anode to +3.3V with a pull-up resistor.
  • Connect IR Receiver Cathode to GND.
  • Connect IR Receiver output to Q1:B via a current limiting resistor.
• Transistor Q1:
  • Connect Q1:E to GND.
  • Connect Q1:C to GPIO 18 (ESP32 SCLK) or GPIO 11 (RPI4 SCLK).
• SPI MOSI:
  • Connect MOSI (GPIO 23 on ESP32 or GPIO 10 on RPI4) to 3.3V or GND.

1. Initialize SPI in Slave Mode:
   • Configure the SPI peripheral to operate in slave mode.
   • Set up SPI to read pulses as clock cycles.
2. Count Pulses:
   • Use an interrupt service routine (ISR) that triggers on SPI data shifts (pulses) to increment a counter variable.

C
#include <SPI.h>

volatile uint32_t pulseCount = 0;

void IRAM_ATTR onSPIClock() {
    pulseCount++;
}

void setup() {
    // Set up SPI Slave
    SPI.begin();
    SPI.setDataMode(SPI_MODE0);
    
    // Attach interrupt to SCK pin
    attachInterrupt(digitalPinToInterrupt(18), onSPIClock, RISING); // For ESP32 SCLK pin. Change to GPIO_X for RPI4
}

void loop() {
    // Do something with pulseCount, e.g., send over network
    // Reset pulseCount after reading if necessary
}

• Debouncing: Ensure your pulse input is debounced if necessary.
• Counter Width: SPI transaction width might limit max count per transaction.

1. Timestamp each pulse to measure velocity.
2. Calculate pulses per time unit to determine velocity.

1. Set up SPI to count pulses.
2. Time the pulses using a timer interrupt or a hardware timer peripheral to get precise readings.
3. Calculate velocity based on the time interval and pulse count.

1. IR Receiver Circuit to Transistor Q1:
   • IR Receiver Anode to 3.3V through a pull-up resistor.
   • IR Receiver Cathode to GND.
   • IR Receiver output to the base of Q1 through a current-limiting resistor.
2. Transistor Q1:
   • Q1:E to GND.
   • Q1:C (collector) to SCK pin of ESP32/RPI4 and to a GPIO configured for high-speed pulse detection.
3. SPI Connections:
   • Connect Q1:C to SPI Clock pin (SCK) of ESP32/RPI4.
     • ESP32: GPIO 18 (SCK).
     • RPI4: GPIO 11 (SCK).
   • Connect MOSI to a stable signal (3.3V or GND is sufficient).
   • CS can be tied to a fixed state or unused.

1. Configure GPIO for Counting Pulses:
   • ESP32 GPIO timer functionality for precise timing.
2. Setup SPI to handle pulses:
   • SPI Slave mode for clock pulse counting.
3. Timer Setup:
   • Use an ESP32 timer to periodically read the pulse count and reset timer.

1. Configure SPI and GPIO:

Cpp
#include <SPI.h>

volatile uint32_t pulseCount = 0;
hw_timer_t *timer = NULL;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;

void IRAM_ATTR onPulse(){
    portENTER_CRITICAL_ISR(&timerMux);
    pulseCount++;
    portEXIT_CRITICAL_ISR(&timerMux);
}

void IRAM_ATTR onTime() {
    portENTER_CRITICAL_ISR(&timerMux);
    Serial.printf("Pulse Count: %d\n", pulseCount);
    // Here calculate velocity or process pulses as needed.
    pulseCount = 0; // reset counter
    portEXIT_CRITICAL_ISR(&timerMux);
}

void setup() {
    Serial.begin(115200);
    
    // Setup SPI
    SPI.begin();
    SPI.setDataMode(SPI_MODE0);
    
    // Configure Pulse Counter GPIO
    pinMode(18, INPUT);
    attachInterrupt(digitalPinToInterrupt(18), onPulse, RISING);
    
    // Setup timer to read pulse count at intervals
    timer = timerBegin(0, 80, true);
    timerAttachInterrupt(timer, &onTime, true);
    timerAlarmWrite(timer, 1000000, true); // Every 1 second
    timerAlarmEnable(timer);
}

void loop() {
    // Main loop, can perform additional tasks if needed
}

Python
import RPi.GPIO as GPIO
import time
from time import sleep

pulse_count = 0
start_time = time.time()

def pulse_callback(channel):
    global pulse_count
    pulse_count += 1

def measure_velocity(pulse_count, time_elapsed):
    velocity = pulse_count / time_elapsed
    return velocity

GPIO.setmode(GPIO.BCM)
GPIO.setup(11, GPIO.IN)  # SPI SCK pin 11

GPIO.add_event_detect(11, GPIO.RISING, callback=pulse_callback)

try:
    while True:
        sleep(1)  # Measure every second
        elapsed_time = time.time() - start_time
        start_time = time.time()
        pulses = pulse_count
        pulse_count = 0
        velocity = measure_velocity(pulses, elapsed_time)
        print(f'Pulses: {pulses}, Time: {elapsed_time:.2f}s, Velocity: {velocity}')
except KeyboardInterrupt:
    GPIO.cleanup()

• Use SPI clock pin (SCK) to capture pulses.
• Use a transistor to condition the pulse signal.
• Count pulses using an interrupt or direct GPIO count method.
• Use a hardware timer (ESP32) or software timing (RPI4) to measure the frequency of pulses, which gives you velocity.