Amplifier HX711 module

Ya’akov

Joined Jan 27, 2019
9,101
Hello, Putri. Welcome to AAC.

Your question is extremely broad and that makes it very hard to answer. Is this for schoolwork?

To get help you should answer your own question as well as you can, including the places where you are confused. This will allow people to understand where to focus.

We can't answer your question as it stands, please describe the flow or the signals from analog input to digital output the way you understand it at this point. Note any difficulties as you go.
 

ericgibbs

Joined Jan 29, 2010
18,830
hi P,
When using a 5V excitation supply to the load cell via the HX711 module, the onboard amplifier can accept a +/-20mV on the A+/- inputs.
So if the gain of the amplifier has been set to 128, this means, considering a +20mV input, that the voltage input to the onboard ADC will be 128 * 20mV = 2.56V.

The ADC will convert this to a 2's Complement format output.
ie:a 24 BIt Signed integer, the MSBit of the integer is the Sign Bit.
So the ADC output will be 7FFFFFF, 8388697 decimal.

Do you follow that so far.??

E
 

ericgibbs

Joined Jan 29, 2010
18,830
Hi P,
Please answer my question in my last post
Do you understand the conversion process I explanation in the post?

If Yes,
What would the ADC output be if the Load Cell voltage output was only +10mV.???

E
 

Thread Starter

putrisyarah

Joined Jul 4, 2022
8
Hi ericgibbs,

Please answer my question in my last post
Do you understand the conversion process I explanation in the post?

I think I'm starting to understand what you're describing

If Yes,
What would the ADC output be if the Load Cell voltage output was only +10mV.???
128 * 20mV = 1.28V.

The ADC will convert this to a 2's Complement format output.
ie:a 24 BIt Signed integer, the MSBit of the integer is the Sign Bit.
So the ADC output will be 7FFFFFF, 8388697 decimal.
can you explain how to get the value 7FFFFFF, 8388697 decimal? the input voltage to the onboard ADC will be 128*20mV = 2.56V.

Putri
 

ericgibbs

Joined Jan 29, 2010
18,830
can you explain how to get the value 7FFFFFF, 8388697 decimal? the input voltage to the onboard ADC will be 128*20mV = 2.56V.
hi,
It is from the datasheet.
Do you know how an ADC module carries out a conversion from a voltage input to a HEX output.??

E
ScreenHunter 20.gif
 

MrChips

Joined Oct 2, 2009
30,780
This is a 24-bit ADC.
The total number of unique states that can be represented by 24-bit value is 2^24 = 16 777 216.
The largest positive number is (2^23) -1, i.e. $7FFFFF = 8 388 607.
The minimum value is $800000 = negative 8 388 608.

In other words
8 388 607 positive values
0
8 388 608 negative values
 

MrChips

Joined Oct 2, 2009
30,780
Ignore HEX for the moment. All digital data is in a binary format, zeros and ones.

An ADC has two reverence voltages, Vref1 and Vref2.
Input voltages within the range Vref1 to Vref2 are converted into 2^n values.
For example, if n = 8, there are 2^8 = 256 voltage levels.
Each voltage step is (Vref2 - Vref1) / 256.

1656943522264.png
 

Thread Starter

putrisyarah

Joined Jul 4, 2022
8
This is a 24-bit ADC.
The total number of unique states that can be represented by 24-bit value is 2^24 = 16 777 216.
The largest positive number is (2^23) -1, i.e. $7FFFFF = 8 388 607.
The minimum value is $800000 = negative 8 388 608.
why does the formula use 2^23 ? 24-bit (2^24) ADC ?

In other words
8 388 607 positive values
0
8 388 608 negative values
Are positive (7) and negative (8) a sign of positive or negative values?

Putri.
 

MrChips

Joined Oct 2, 2009
30,780
why does the formula use 2^23 ? 24-bit (2^24) ADC ?


Are positive (7) and negative (8) a sign of positive or negative values?

Putri.
No. Only the most significant bit represents the sign.

For example, for a 4-bit ADC
Positive values are:
0111
0110
0101
0100
0011
0010
0001

0000 - zero

negative values:
1111
1110
1101
1100
1011
1010
1001
1000

This is known as 2's complement binary representation.
https://en.wikipedia.org/wiki/Two's_complement
 
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