ADC selection for Weight Scale

Hi Roberto,

Welcome to the forum!  I would not recommend the ADS1212.  It is an old design and not very easy to use.  There are some other considerations such as type of interface (SPI, I2C, UART, etc.) as well as rate of conversion.  Also, you provided some information that seems to be contradictory.  For example, you mention 4 load cells or 3 load cells, then later you mention no more than 2 channels.  You also mention differing load cell sensitivities.  This will make a difference on which ADCs you can use.  Can you be a little more specific on what you really need?  Perhaps your price range as well?

The ADS1220 and the ADS122U04 are very similar devices except the ADS1220 is SPI and the ADS122U04 is UART interface.  These devices will come close to achieving 50k noise-free counts at 20sps for a 3mV/V sensitivity.   The ADS1232 is a 2 channel input ADC and there is also has a similar 4 channel input device the ADS1234.  However the ADS1234 does not have an internal temperature sensor option.  Depending on the total number of inputs actually required, you could take a look a the ADS124S06 or ADS124S08.  None of above ADCs require an external amplifier. I can help narrow down the options with further information.

Best regards,

Bob B

Hello Bob, let me try explain it for you:

my device will work with trucks for feed cows, and this system have many configurations for load cell, example:

some cases i use my device (weight scale) and need use 4 load cells, all in parallel, all in same AD input, all have 3mV/V and all are same capacity.

other case, i nee use my device (weight scale) but need use 3 load cells, all in parallel, all in same AD input, all have 0,5mV/V and all are same capacity.

in all cases will work with same capacity and same mV/V, and always use same AD input.

i can work with AD about +- 18 USD.

i saw the ADS1220 and like it, have many examples for ARM Arduino PIC etc... and saw ADS122U04 and like it because UART interface, its a new device, don't find goods examples..

what you think if i use ADS1220?

do you understand my application?

Hi Roberto,

I guess my final question is you intend to use 2 different sensitivity load cells, 3mV/V and 500uV/V is that correct?   Basically you want to build a large scale version similar to this TI Design:

http://www.ti.com/tool/tida-00765

The above design uses the ADS1220 and can achieve 15000 noise-free counts with a 1mV/V load cell.  So it seems reasonable that you can achieve the precision you require for 3mV/V sensitivity, but not for 500uV/V sensitivity.  I'm not sure that the ADS1232 will be able to achieve 50000 noise-free counts at 500uV/V.  It may come close with some averaging.  One other device to consider is the ADS1262.

Best regards,

Bob B

Hello Bob,

for same weight kits i don't use different load cell sensitivity. if my kit have 4 load cell, all are same sensivity.
if change sensivity, change for all load cells.

about design, i think its same...

i have a question about load cell, if you can help me, if i use 4 load cells (in parallel wiring) in same AD input, and all are 3mV/V, what counts will have with ADS1220? the Exitation are 5V

Hi Roberto,

Look at the ADS1220 datasheet on page 59 of the bridge example.  Substitute your values into the equation 42.  The Repeatability for a 50kg load cell with 3mV/V excitation will be (50kg/15mV)*0.41uV (Vpp noise at gain 128) is approximately 1.4 grams.  Perhaps with some additional averaging you can improve that somewhat.  But just in raw noise-free counts (50kg/1.4) is about 36585.  I would say this device would be marginal for your application.

Best regards,

Bob B