75 lines
2.5 KiB
Python
75 lines
2.5 KiB
Python
import spidev
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import time
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DEBUG = False
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class MCP3208:
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def __init__(self, bus=0, device=0):
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# Initialize SPI bus and device
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self.spi = spidev.SpiDev()
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self.spi.open(bus, device) # Default SPI bus 0, device 0 (you can change as needed)
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self.spi.max_speed_hz = 1000000 # Adjust based on your needs (e.g., 1MHz)
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self.spi.mode = 0b00 # Set SPI mode (Mode 0 for MCP3208)
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def read(self, channel):
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"""
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Read the ADC value from the specified channel (0-7).
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"""
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# MCP3208 is a 12-bit SPI ADC. Communication requires sending a 3-byte command and receiving a 3-byte response.
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# The bits in the command sequence are structured as follows:
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# Command Byte (8 bits):
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# | Start (1) | Mode (1) | Channel (3) | Padding (3) |
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# The MCP3208 responds with 3 bytes:
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# - Byte 1: Contains the highest bit (bit 11) of the 12-bit ADC result.
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# - Byte 2: Contains bits 10-3 of the ADC result.
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# - Byte 3: Contains bits 2-0 of the ADC result.
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# Ensure the channel is valid (0-7)
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if channel < 0 or channel > 7:
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raise ValueError(f"Channel must be between 0 and 7. (current channel={channel})")
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# Construct the command byte sequence:
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# - Start bit (1) -> 1000 0000 (0x80)
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# - Single-ended (1) -> 1100 0000 (0xC0)
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# - Channel (3 bits) shifted into position
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cmd = 0x80 # Start bit: 1000 0000
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cmd |= 0x40 # Single-ended mode: 1100 0000
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cmd |= (channel & 0x07) << 3 # Move channel number to bits 5-3
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# Send the command and receive the 3-byte response
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ret = self.spi.xfer2([cmd, 0x00, 0x00]) # Send 3 bytes, receive 3 bytes
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if DEBUG:
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print(f"result[0]: {bin(ret[0])}, result[1]: {bin(ret[1])}, result[2]: {bin(ret[2])}")
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# Extract the 12-bit ADC result from the received bytes:
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val = (ret[0] & 0x01) << 11 # Extract bit 11 (MSB)
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val |= ret[1] << 3 # Extract bits 10-3
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val |= ret[2] >> 5 # Extract bits 2-0 (shift down)
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return val & 0x0FFF # Mask to ensure only the lower 12 bits are used
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def close(self):
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"""Close SPI connection."""
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self.spi.close()
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# Example usage:
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if __name__ == "__main__":
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adc = MCP3208()
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try:
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while True:
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for i in range(8):
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adc_value = adc.read(i)
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print(f'ADC[{i}]: {adc_value}')
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time.sleep(0.5)
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finally:
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adc.close()
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