9 Replies Latest reply on Jan 16, 2019 4:15 AM by javi_983821

    Weight Scale

    shbrc_293306

       Hello! I am beginner in psoc.

         
          I want to make a weight scales where i need to read a value from the load cell sensor with (5v excitation voltage).   
         
              
         
          I have PSoC development board cy8ckit-001, and I like to Programming with cy8c38 Family (CY8C3866AXI-040),   
         
          DelSig_ADC 20bit,bidirectional positive and negative value, and to see the value in the LCD screen.   
         
          Can anyone help me with any "ready" project oer sample in psoc creator.   
         
              
         
          Thank you.   
        • 1. Re: Weight Scale
          DaKn_263916

          It would help if you post or URL for the laod cell datasheet.

             

           

             

          Basically 80% of the project can be done by placing the delsig on schematic, right click,

             

          and you pick "find example project" for A/D, and import it into your build or use standalone.

             

           

             

          Regards, Dana.

          • 2. Re: Weight Scale
            shbrc_293306

             Thank you for your quick reply.

               

            http://www.loadcell-china.com/?mod=product&act=detail&id=41&categoryId=42&oneId=222222&type=1

               

            Regards

               

            Braka

            • 3. Re: Weight Scale
              DaKn_263916

              For starters you need an Instrumentation Amplifier, PSOC can do that,

                 

              but at less precision than is avaiable as a dedicated IA chip. Plus the load

                 

              cell, if excited by > PSOC Vdda, implies the IA cannot be internal to PSOC,

                 

              due to its CM input range limitation on inputs.

                 

               

                 

              I have attached some info that may be of help. Further info here on IA design -

                 

               

                 

              http://www.ti.com/lit/an/slyt226/slyt226.pdf
              http://www.analog.com/static/imported-files/application_notes/AN-244.pdf
              http://www.analog.com/static/imported-files/design_handbooks/5812756674312778737Complete_In_Amp.pdf

                 

               

                 

              I strongly recommend you set an error/precision/accuracy goal, then do an end

                 

              to end analysis of the errors to see if the PSOC IA solution will suffice.

                 

               

                 

              Regards, Dana.

              • 4. Re: Weight Scale
                shbrc_293306

                Thanks for the help Dana!

                   
                    This is my big problem because i'm beginner and i'm not able to select the right components.   
                   
                    For this reason i'm looking for a ready avaiable project refer to this document http://www.cypress.com/?docID=34330 ,   
                   
                    Figure 5. Integrated Weigh scale solution based on a Cypress PSoC 3 device .   
                • 5. Re: Weight Scale
                  DaKn_263916

                  Try contacting the authors, their email address is at end of this article -

                     

                   

                     

                  http://www.eetimes.com/design/industrial-control/4233537/Weighing-scale-design-Measure-signals-accurately

                     

                   

                     

                  Regards, Dana.

                  • 6. Re: Weight Scale
                    educ_284901

                    Hi BRAKA, do you have any thing done with weight scale??? Because I'm having the same problem as you. If you did any can you kindly lend me your project? I will credit that it is yours. Or at least lend me a hand with the weight scale.

                       

                     

                       

                    Regards

                       

                    Edgardo from Buenos Aires-Argentina

                    • 7. Re: Weight Scale
                      DaKn_263916
                              My guess is BRAKA is no longer monitoring this thread from a year ago. Regards, Dana.   
                      • 8. Re: Weight Scale
                        userc_40585

                         have anyone any thing done with weight scale??? If you did any can you kindly lend me your project?  Or  lend me a hand with the weight scale.

                           

                        email:stecscales@yahoo.com

                           

                        Thanks

                           

                         

                           

                        Regards

                        • 9. Re: Weight Scale
                          user_3271306

                          Hello Friends

                          we have a requirement to design a weighing system to weigh a variable Load in the range 0-20 Kgs as accurately as possible , which will be placed above a fixed weight of about 1000 Kgs.

                           

                          Can any one suggest a possible solution?

                           

                          Regards

                          Vijayan. India

                          • 10. Re: Weight Scale
                            javi_983821

                            Hello Vijayan,

                             

                            Hopefully these comments are at least little bit useful for you.

                             

                            Your question contains so few details that any suggestion may go horribly far from the answer you are looking for...

                            E.g  you should take a different approach depending on how many measurement systems/products will be produced.

                             

                            Anyway, here goes. I would suggest you would start to narrow down the solution by first understanding the mechanical aspects of the construction and minimum accuracy requirement you will need to meet. And as always, you need to know your feasible price range for the end solution.

                             

                            Load cell = piece of metal with strain-gauge attached to the side of it.

                             

                            You need:

                            Load cell + AFE (analog front end) + MCU

                             

                            First: You need to understand how much mechanical strain the piece of metal (load cell) will have to endure. Not just static load but also dynamical impacts etc. and how much over the nominal value the metal should hold static weight before starting to yield (safe requirements).

                            --> now you can look for load cells or know the cross-section are of your metal piece and can figure out what kind of strain-gauge is good for you.

                             

                            (If you are designing a product: read about strain-gauges components. HBM has very good material available about their products as well as a lot of general info. If you are not able to always calibrate or be able to just measure changes to "empty scale", you should read also about how strain-gauges drift over the years.)

                             

                            Second (a): Select suitable load-cell. If you find product with large gauge factor you need less from your AFE. (make sure mechanical requirement are met.)

                            Second(b) "building a product": Now you should know mechanical details about your load cell metal piece in order to select suitable strain gauge. (material, cross-section area for Tensile Strength calculation(UTS and YTS) --> then you can calculate strain with max. load (full scale) --> select strain gauge.

                             

                            Now, your load cell material should be known not the yield under any possible condition and strain gauge component is selected to endure max. stretching of the metal under full load.

                             

                            Okey, now you can calculate what kind of excitation voltage you will get with your input voltage to the bridge measurement ( at least half bridge would be advisable) and with the load measurement accuracy you are looking for.

                             

                            third:

                            TI has quite good AFEs for this purpose. I would start there. Select top of the line AFE component, some 24 to 32 bits model.

                            check that your full scale reading is in under max. input voltage value of AFE. if not, adjust.

                            Calculate how many AFE bits is your accuracy requirement is (converted to excitation volts). Make sure your requirement is well over the AFEs probable noise level and that your AFE is more accurate than your accuracy requirement (4 times more accurate is good, 10 times is golden).

                             

                            That's it, more or less. Connection to e.g. PSOC is quite simple.

                             

                            btw. If the "about 1000kg" load is always present unchanged and you are able to calibrate the measurement circuit, you could calibrate the static load off by adjusting the measurement bridge circuits balance(if adjustable or self designed). Then, when starting near zero kg load (meaning near zero excitation voltage), you could perhaps supply larger input voltage to bridge circuit and get larger excitation voltage with "full 20 kg load" that would be still under AFE´s max input range . Well, there where a lot of "if"s in the last chapter...

                             

                            I just noted how long it has been since you posted the question......;)

                            well, perhaps somebody will get some useful info out of this answer.

                             

                            Best regards,

                            Janne, Finland