1 2 Previous Next 15 Replies Latest reply on May 6, 2013 5:16 AM by userc_40792

    unable to make the insamp to work !!!!

      hello everybody,




      I need some advice(s) because I am not able to make the differential amplifier to work ...


      I have two square waves around 100KHz, 0 to 50mV


      one of the square wave is the reference and is a "pure" 100KHz square wave


      the other is moving with a sensor, between 0 and 50mV too


      I want to amplify the difference between the two signals.


      I tried the insamp, with two or three amps, the 2 signals are declared as analoginput, the reference is vss


      the output of the insamp is an analogoutbuf


      the output I can see is only made of noise... it moves a very little 2mV maximum


      it should move between 0 and 50mV * 16 = 800mV


      There is something i miss, and I really want to know what


      there was an appnote for interfacing a mpx pressure sensor to a psoc, but it doesnt seems to be on the cypress site ?


      this appnote seems really to be like the measures I want to make


      can someone help me ? point me the things to verify when using the insamp and that I could have missed ?


      many thanks.

        • 1. Re: unable to make the insamp to work !!!!

           I have attached the project and document used for the pressure sensor example. Can you please let me know how are you configuring your Instrumentation amplifier? In which power mode you have started this module? If possible, please provide your project.




          Best regards,



          • 2. Re: unable to make the insamp to work !!!!

             It seems that I am unable to attach the zip file. Let me know your email address, I'll email it to you.




            Document is attached with this response.




            Best regards,



            • 3. Re: unable to make the insamp to work !!!!

              thanks for your quick answer !


              my email is jyp2 at free.fr


              I will make screen dump of the project to explain within a few days.



              • 4. Re: unable to make the insamp to work !!!!

                btw the pressure sensor is interesting.


                the pressure sensor requires dc voltage to measure


                I saw also another example with a humidity sensor


                this one should be ac voltages and would be better to me


                but also this project is in google caches, but not anymore in cypress app notes ???



                • 5. Re: unable to make the insamp to work !!!!



                  in fact after some researches, I started a new project from scratch


                  with one pwm giving me my 100KHz signal


                  then my measuring bridge outside the psoc


                  the two signals coming back in the insamp, and it works !!!!


                  so it seems that if you manipulate "too much" a project, nothing works with the insamp


                  I did the exact same thing with the two projects and in the project I use for some weeks it simply doesnt work.


                  in a fresh new project the same things work... I use psoc designer 5.1




                  also it works, but only the 2 amps insamp... the 3 amps diff amplifier doesnt work too, I get garbare at the output...


                  well it works for my project now so let's say the case is closed but still I have some things I would like to understand...




                  ps: if someone has the app note about the humidity sensor and the psoc1 it interests me... thanks.

                  • 6. Re: unable to make the insamp to work !!!!

                     I have sent you both the projects at email address provided by you.




                    Best regards,



                    • 7. Re: unable to make the insamp to work !!!!



                      sorry to bother you but I received nothing from you, even in the spam folder ...


                      why are these app notes removed from the cypress site ?


                      can you give here a link to them so that i can download it (and may other people ?)



                      • 8. Re: unable to make the insamp to work !!!!

                         I sent you the projects but email bounced back saying invalid email address. Can you share your email address once again.




                        Best regards,



                        • 9. Re: unable to make the insamp to work !!!!
                                  i use cy8c29466-24sxi and i have problem whit extrakting commen mode signal howe can i conect a output pin or buffer to insamp-3? it dosnt any wire . perhaps i must write c cod but i dont know how? pleas help me.   
                          • 10. Re: unable to make the insamp to work !!!!



                            Can someone help from Cypress?


                            Im facing a similar problem with the 3 opamp INSAMP peripheral.


                            Output always stays at ~2.44V irrespective of the input variation.


                            A similar config with the PGA works perfectly (though there is only one input).


                            Rgds, Deiv




                            DETAILS OF SETUP


                            Device: CY8C29466-24PXI


                            Analog range Vdd/2 +/- Vdd/2


                            INSAMP module parameters: Differential gain = 2, Converter gain = 1


                            Configuration: POSIN - P0_1, NEGIN - P0_0, OUTPUT of INSAMP to AnalogBuffer_1 to P0_5


                            IDE: PSoC Designer 5.3

                            • 11. Re: unable to make the insamp to work !!!!

                              It is always advisable to post the complete project here so that we all can have a look at. Sometimes a setting can hinder the function of a usermodule.


                              To upload a project use the "Archive Project" function and upload the resulting archive here (Do not use Chrome, it does not work when uploading, use ms ie)


                              One of the pitfalls might be the polarity of the clock when chaining SC-blocks.





                              • 12. Re: unable to make the insamp to work !!!!
                                        Ensure the Referrence voltage selection. That is affect to Input voltage range and OUTPUT VOLTAGE RANGE also. I presume REF=AGND is working well usually. Try this setting. Thank you.   
                                • 13. Re: unable to make the insamp to work !!!!

                                  Some possibilities -




                                  1) You set the CM output per the following notes -


                                  This parameter only applies to the three opamp topology. The common mode node connects the two continuous time blocks at the “ends” of their resistor strings (see the figure “Three Op-Amp Instrumentation Amplifier Simplified Schematic”). The common mode voltage derived from this node is useful in many applications for improving noise immunity through shielding by such means as guard traces. This voltage may be connected to the analog column output bus and its associated analog output buffer through either of the CT PSoC blocks, INV or NON_INV, by setting this parameter. In addition to these two options, the CommonModeOut parameter may be set to “None.”


                                  One of the two CT blocks, either INV or NON_INV, will lie in the same analog column as the switched capacitor CONVERT block. If the AnalogBus parameter is set to Enable, either set CommonModeOut to “None” or set it to the block that lies in the column not shared by the CONVERT block. Otherwise, the output of the INSAMP will be connected in a feedback loop to the common mode point and the output behavior will not correspond to expectations.




                                  2) Column clock for the SC portion of the IA set to ~ <= 1 Mhz ?




                                  3) The CommonModeOut in IA properties set to No Connect ?




                                  4) Your P0_0 and P0_1 set to Analog Input, High Z Analog ?




                                  5) Inputs meet -



                                  • 14. Re: unable to make the insamp to work !!!!

                                    5) Inputs meet CM range shown in charts in datasheet ?




                                    6) The following has been coded -



                                    INSAMP_SetGain(INSAMP_G3_20);         // Use the proper value for your gain setting       



                                    Regards, Dana.

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