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3.1.5 Battery Indicator(MCP3008)

Note

Depending on your kit version, please identify whether you have ADC0834 or MCP3008 and proceed with the matching section.

Introduction

In this project, we will make a battery indicator device that can visually display the battery level on the LED Bargraph.

Warning

Do not use battery components that exceed 3.3V to avoid overloading, which may damage the chip or Raspberry Pi.

Required Components

In this project, we need the following components.

Schematic Diagram

T-Board Name	physical	wiringPi	BCM
SPICE0	Pin 24	10	8
SPIMOSI	Pin 19	12	10
SPIMISO	Pin 21	13	9
SPISCLK	Pin 23	14	11
GPIO25	Pin 22	6	25
GPIO12	Pin 32	26	12
GPIO16	Pin 36	27	16
GPIO20	Pin 38	28	20
GPIO21	Pin 40	29	21
GPIO5	Pin 29	21	5
GPIO6	Pin 31	22	6
GPIO13	Pin 33	23	13
GPIO19	Pin 35	24	19
GPIO26	Pin 37	25	26

Experimental Procedures

Step 1: Build the circuit.

Step 2: Set up the SPI interface and install the spidev library (see SPI Configuration for detailed instructions). If you have already completed these steps, you can skip this.

Step 3: Go to the folder of the code.

cd ~/davinci-kit-for-raspberry-pi/python-pi5

Step 4: Run the executable file.

sudo python3 3.1.5-2_Battery_indicator_zero.py

After the program runs, give the 3rd pin of MCP3008 and the GND a lead-out wire separately and then lead them to the two poles of a battery separately. You can see the corresponding LED on the LED Bargraph is lit up to display the power level (measuring range: 0-5V).

Warning

If there is an error prompt RuntimeError: Cannot determine SOC peripheral base address, please refer to If gpiozero doesn’t work.

Code

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like davinci-kit-for-raspberry-pi/python-pi5. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3

import LCD1602
from gpiozero import LED, Buzzer, Button
import spidev
import time
import math

# Initialize joystick button, buzzer, and LED
Joy_BtnPin = Button(22)  # GPIO22, Pin15
buzzPin = Buzzer(23)     # GPIO23, Pin16
ledPin = LED(24)         # GPIO24, Pin18

# Set initial upper temperature threshold
upperTem = 40

# Initialize SPI for MCP3008 (Bus 0, CE0 -> GPIO8 / Pin24)
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1000000  # 1 MHz

# Initialize LCD (I2C address 0x27, backlight on)
LCD1602.init(0x27, 1)

def read_adc(channel):
    """
    Read analog value from MCP3008
    """
    if channel < 0 or channel > 7:
        return -1
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    value = ((adc[1] & 0x03) << 8) | adc[2]
    return value

def get_joystick_value():
    """
    Reads the joystick values and returns a change value based on the joystick's position.
    """
    x_val = read_adc(1)
    y_val = read_adc(2)
    if x_val > 800:
        return 1
    elif x_val < 200:
        return -1
    elif y_val > 800:
        return -10
    elif y_val < 200:
        return 10
    else:
        return 0

def upper_tem_setting():
    """
    Adjusts and displays the upper temperature threshold on the LCD.
    """
    global upperTem
    LCD1602.write(0, 0, 'Upper Adjust: ')
    change = int(get_joystick_value())
    upperTem += change
    strUpperTem = str(upperTem)
    LCD1602.write(0, 1, strUpperTem)
    LCD1602.write(len(strUpperTem), 1, '              ')
    time.sleep(0.1)

def temperature():
    """
    Reads the current temperature from the sensor and returns it in Celsius.
    """
    analogVal = read_adc(0)
    Vr = 3.3 * analogVal / 1023.0  # Voltage across the fixed resistor
    if Vr == 0:
        return 0  # Prevent division by zero
    Rt = 10000.0 * (3.3 - Vr) / Vr  # Adjusted formula: thermistor voltage is (3.3 - Vr)
    temp = 1 / (((math.log(Rt / 10000.0)) / 3950.0) + (1 / (273.15 + 25.0)))
    Cel = temp - 273.15
    return round(Cel, 2)

def monitoring_temp():
    """
    Monitors and displays the current temperature and upper temperature threshold.
    Activates buzzer and LED if the temperature exceeds the upper limit.
    """
    global upperTem
    Cel = temperature()
    LCD1602.write(0, 0, 'Temp: ')
    LCD1602.write(0, 1, 'Upper: ')
    LCD1602.write(6, 0, str(Cel))
    LCD1602.write(7, 1, str(upperTem))
    time.sleep(0.1)
    if Cel >= upperTem:
        buzzPin.on()
        ledPin.on()
    else:
        buzzPin.off()
        ledPin.off()

# Main execution loop
try:
    lastState = 1
    stage = 0
    while True:
        currentState = Joy_BtnPin.value
        if currentState == 1 and lastState == 0:
            stage = (stage + 1) % 2
            time.sleep(0.1)
            LCD1602.clear()
        lastState = currentState
        if stage == 1:
            upper_tem_setting()
        else:
            monitoring_temp()
except KeyboardInterrupt:
    LCD1602.clear()
    spi.close()

Code Explanation

This Python program runs on a Raspberry Pi. It uses an MCP3008 analog-to-digital converter to read temperature data from an analog sensor. A joystick is used to adjust the temperature threshold, and an LCD1602 display shows the current temperature and threshold. A buzzer and LED are triggered when the temperature exceeds the threshold.

1. Import Required Libraries

   #!/usr/bin/env python3
   
   import RPi.GPIO as GPIO
   import spidev
   import time
   import math
   import LCD1602
   

   • RPi.GPIO is used for controlling GPIO pins.

   • spidev communicates with MCP3008 using SPI.

   • math is needed for temperature conversion calculations.

   • LCD1602 controls the LCD display.

2. GPIO Setup

   JOY_BTN_PIN = 22
   BUZZER_PIN = 23
   LED_PIN = 24
   
   GPIO.setmode(GPIO.BCM)
   GPIO.setup(JOY_BTN_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)
   GPIO.setup(BUZZER_PIN, GPIO.OUT)
   GPIO.setup(LED_PIN, GPIO.OUT)
   

   • Assigns pins for joystick button, buzzer, and LED using BCM numbering.

   • Configures the joystick button with a pull-up resistor and sets output pins LOW initially.

3. SPI and LCD Initialization

   upperTem = 40  # Default temperature threshold
   
   spi = spidev.SpiDev()
   spi.open(0, 0)
   spi.max_speed_hz = 1000000  # 1 MHz
   
   LCD1602.init(0x27, 1)
   

   • Initializes SPI communication for the MCP3008.

   • Sets up the I2C LCD1602 at address 0x27.

4. Read ADC Channel

   def read_adc(channel):
       if channel < 0 or channel > 7:
           return -1
       adc = spi.xfer2([1, (8 + channel) << 4, 0])
       value = ((adc[1] & 0x03) << 8) | adc[2]
       return value
   

   • Sends SPI commands to MCP3008 to read analog voltage from the selected channel (0–7).

   • Returns a 10-bit result between 0 and 1023.

5. Joystick Direction Input

   def get_joystick_value():
       x_val = read_adc(1)
       y_val = read_adc(2)
       if x_val > 800:
           return 1
       elif x_val < 200:
           return -1
       elif y_val > 800:
           return -10
       elif y_val < 200:
           return 10
       else:
           return 0
   

   • Reads horizontal (X) and vertical (Y) joystick movement and translates that into a change in threshold:

     • Up/Down adjusts by 10.

     • Left/Right adjusts by 1.

6. Adjust Temperature Threshold

   def upper_tem_setting():
       global upperTem
       LCD1602.write(0, 0, 'Upper Adjust: ')
       change = int(get_joystick_value())
       upperTem += change
       strUpperTem = str(upperTem)
       LCD1602.write(0, 1, strUpperTem)
       LCD1602.write(len(strUpperTem), 1, '              ')
       time.sleep(0.1)
   

   • Allows the user to change the upperTem threshold via joystick.

   • Updates LCD to display the current threshold value.

7. Calculate Temperature from Analog Sensor

   def temperature():
       analogVal = read_adc(0)
       Vr = 3.3 * analogVal / 1023.0
       if Vr == 0:
           return 0
       Rt = 10000.0 * (3.3 - Vr) / Vr
       tempK = 1.0 / (((math.log(Rt / 10000.0)) / 3950.0) + (1.0 / (273.15 + 25.0)))
       Cel = tempK - 273.15
       return round(Cel, 2)
   

   • Converts voltage reading to resistance, then uses the Steinhart-Hart equation to compute the temperature in Celsius.

8. Monitoring Mode

   def monitoring_temp():
       global upperTem
       Cel = temperature()
       LCD1602.write(0, 0, 'Temp: ')
       LCD1602.write(0, 1, 'Upper: ')
       LCD1602.write(6, 0, str(Cel))
       LCD1602.write(7, 1, str(upperTem))
       time.sleep(0.1)
       if Cel >= upperTem:
           GPIO.output(BUZZER_PIN, GPIO.HIGH)
           GPIO.output(LED_PIN, GPIO.HIGH)
       else:
           GPIO.output(BUZZER_PIN, GPIO.LOW)
           GPIO.output(LED_PIN, GPIO.LOW)
   

   • Displays the current temperature and threshold.

   • Activates buzzer and LED if the current temperature exceeds the threshold.

9. Main Loop

   try:
       lastState = GPIO.input(JOY_BTN_PIN)
       stage = 0
       while True:
           currentState = GPIO.input(JOY_BTN_PIN)
           if currentState == GPIO.HIGH and lastState == GPIO.LOW:
               stage = (stage + 1) % 2
               time.sleep(0.1)
               LCD1602.clear()
           lastState = currentState
   
           if stage == 1:
               upper_tem_setting()
           else:
               monitoring_temp()
   

   • Uses joystick button press to toggle between:

     • stage 0: temperature monitoring

     • stage 1: threshold adjustment

10. Cleanup on Exit

except KeyboardInterrupt:
    pass

finally:
    LCD1602.clear()
    GPIO.cleanup()
    spi.close()

• Ensures GPIO and LCD are reset on program termination (e.g., Ctrl+C).