Error with Reading 0v

natep · January 10, 2024, 7:40pm

I am using the MCP3248 0-10V ADC. I modified the code from the posted code on GitHub to read 2 pressure transducers that are hooked up to channels 1 and 2 with channels 3 and 4. My problem is under vacuum the lowest voltage reading I can get is ~0.07V obscuring the bottom bit of data. On channels 3 and 4, it also reads ~0.07V with no wire hooked up to it. My code also prints the values in data (data[0] and data[1]) and data[1] seems to read a minimum of 21 and never dips below that.

I am currently reading and polling for 2 bytes (16 bits).

Is there a configuration command or something that I am missing or using incorrectly?

Additionally, it would be appreciated if anyone has more code examples or documentation that I can use.

Bhaskar · January 11, 2024, 1:49pm

are you using this

natep · January 12, 2024, 3:02pm

I’m using this:

natep · January 12, 2024, 3:04pm

And this is the code I am using:

github.com

bhaskar-anil429/MCP3428_0-20V_ADC/blob/master/0-20V_ADC_16bit.py

# Distributed with a free-will license.
# Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
# MCP3428
# This code is designed to work with the MCP3428_I2CADC I2C Mini Module available from ControlEverything.com.
# https://shop.controleverything.com/collections/analog-to-digital-converters
import smbus
import time
DL = 0
DL1 = 0.5
address = 0x68
# Get I2C bus
bus = smbus.SMBus(1)

# MCP3428 address, 0x68(104)
# Send configuration command
#               0x18 Continuous conversion mode, Channel-1, 16-bit Resolution, gain 1

while True:
        bus.write_byte(address, 0x18)
        time.sleep(DL1)

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natep · January 12, 2024, 3:15pm

Also to amend my initial post it is not reading below .007V not .07V.

Below is the screenshot of the system running (currently the transducers should be at the same pressure, upstream is a 0-1000 PSI downstream is 0-5PSI so upstream will be less accurate but they should be close. The first number printed is data[0] and the second number is data[1] but data[1] never goes below 21.
Channel 4’s is empty but is still reading that minimum of ~0.007
I now connected channel 3’s input straight to ground and am still reading that minimum of 0.007V.