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AFE4300 Weight-Scale

An Zo
Prodigy 215 points
Other Parts Discussed in Thread: AFE4300, AFE4300EVM-PDK, MSP430F449

Hello, i'm trying to use AFE4300 to measure weight, using external load-cells. Do you have any detailed instruction for weight-scale function like the SBAA202 for impedance measurement?

And in the BOM, what is the use of R95, R96, R97, R98?

Thanks

  • 0
    TI__Expert 6320 points

    Hi An,

    We received your questions regarding the AFE4300 and will get back with you shortly with a response.

    Chuck Smyth

  • 0 in reply to Chuck Smyth
    TI__Mastermind 18285 points

    An,

    Unfortunately we do not have any additional documents describing how to use the weight scale other than the user's guide and that datasheet.


    Those resistors are part of the anti-aliasing filter on the input. This is found on the weight scale input signal page of the schematic found on page 40 of the user's guide.

  • 0 in reply to Amy Schnoor
    Prodigy 215 points

    Hello, thank you for your answer.

    I just found something related to weight-scale function in the demonstration code AFE4300EVM-PDK, and i have some other questions:

    1. In the MSP430F449_AFE4300Controller.c file, line 462, it was written:

    spiWrite(0x09,0x0005); 

    It means DEVICE_CONTROL1[14:13] are set = 0b00. But in the datasheet, it is said that "Not used. Always write 1".

    Can you explain me the difference here? What happens if the "not used" bits are not set correct?

    2. At line 458, it was written:

    spiWrite(0x0D,0x003F); // Max Gain, DAC to "Zero"

    As i understand from the datasheet, the OFFSET_DAC_VALUE[5:0] were set = 111111, means -1 x 31.2mV offset correction. How could it be "Zero" like the comment?

    3. Line 461, spiWrite(0x01,0x4143);

    so ADC_CONTROL_REGISTER1 bits[3:0] were set = 0011, but in the datasheet it is said: "Always write 0000. At power up, these bits are set as 0011". So one has to set the bits as 0000 or 0011 ?! I thought it implies after power up, the bits are automatically set as 0011, and one has to rewrite them by 0000?

    Thank you

  • 0 in reply to An Zo
    TI__Mastermind 18285 points

    An,


    Our software is given as a starting point to customers and is given as is.

    1. This sets the DEVICE_CONTROL1 register to power up the front-end, power down the BCM, and power up the weight scale. Bits 2,1,0 respectively.

    2.The comment is a typo

    These bits set the value for the DAC used to correct the input offset of the weight-scale front-end. The correction is made at the second stage. The offset correction at the output of the first stage is given by OFFSET_DAC_VALUE x 31.2 mV. Note that OFFSET_DAC_VALUE is a number from -32 to 31, in twos complement; default is ‘000000’.

    3. We just set them to the power up defaults.