1 2 Previous Next 22 Replies Latest reply on Jun 23, 2015 10:04 AM by user_14586677

    Yet another frequency measurement question

    un3x

       I've googled and found lots of questions from people trying to get something done about how to measure frequency. Every answer starts with "what frequencies?". And the next question is "include archive". OK, so the archive is attached. In the event more than one project is in it, I'm using "ADC_Differential_Preamplifier01.cydsm" and no other projects in the workspace.

         

       

         

      Platform is CY8CKIT-049-42xx. I sucessfully implemented the example project ADC_DiffPreamplifier.pdf:

         

         

       

         

      Here's the circuit implemented from the example:

         

       

         

         

       

         

      The difference is that I have implemented Rg as the round gray variable resistor to the right of the breadboard. Input is a cheapy Electret Condenser Microphone from Amazon. My R1 and R2 are 99xx ohms, so very close to 10k. Anecdotally, Rg is somewhere near 3k. 

         

       

         

      Notice on the o-scope, there's a 500mV p-p signal. Yeah, that's 60 Hz with a 1.25 second period additional signal on it that's about half its amplitutde. Thankfully, the microphone seems perfectly suited to this dual op-amp differential amplifier (referred to as the first half of an instrumention amplifier). 

         

       

         

      So what frequencies?

         

       

         

      80 to 120 Hz with great resolution. 65 to 140 is the total range I care about. And definitely nothing below 65... I desire to rid this world of 60Hz. I'd really like to know when a primary frequency heard is near 100 or 110 Hz and be able to differentiate within 1Hz all around there. 

         

       

         

      From all that I've read, it would seem most people are focussed on higher frequencies and the sampling in the example seems MUCH too frequent. Most software FFTs seem to be in the dozens of points, while it would seem I need hundreds if not thousands of points to effectively sample ~100Hz. 

         

       

         

      I'm a total noob to this stuff, but can't suck too bad if I've managed to coax a CY8CKIT-049-42xx to do this much. I'd appreciate any and all advice, pointers, and clues about how to accomplish this mission via software, logic in the PSoC, or both. I'll keep researching...

         

       

         

      Thanks,
      Chris 

        • 1. Re: Yet another frequency measurement question
          un3x

           Oh here's a pic of DC coupling of the same. The circuit is biased around 4VDC. Center gradient is at 0VDC. 

             

           

             

             

           

             

          Interestingly enough, when there's input, it would seem the DC bias drops to 2.5V and the signal is AC p-p from there. The above waves were made by rubbing my foot back and forth across the bottom of the Tower PC all of this is sitting upon.

             

           

             

          I have no doubts that the PSoC will be able to detect the frequencies I'm wanting. I couldn't immediately notice if there are higher frequencies, but tapping my foot on the floor is pretty easy to see on the Scope.

             

           

             

          Thanks,
          Chris

          • 2. Re: Yet another frequency measurement question
            user_14586677

            Important is the matching of the10K's, analysis attached. That controls your

               

            CMR thru the OpAmp diff stage. So sounds like your 60 Hz is not CM ?

               

             

               

            www.dropbox.com/s/plck7e95v7pw33c/CMR%20Analysis%20IA.pdf

               

             

               

            Note Aol G matching affects CMR as well -

               

             

               

                

               

                      http://www.cypress.com/?app=forum&id=2492&rID=82151     IA CMR Analysis

               

             

               

            80 to 120 Hz with great resolution. 65 to 140 is the total range I care about. And definitely nothing below 65... I desire to rid this world of 60Hz. I'd really like to know when a primary frequency heard is near 100 or 110 Hz and be able to differentiate within 1Hz all around there.

               

             

               

            Attached 2 different freq measuring approaches.

               

             

               

            www.dropbox.com/sh/prpc74bdga7yijz/AAAeC-Dmmn5sYbWwRrl0-ZUoa

               

             

               

            Insofar as getting rid of 60 Hz a Sallen Key notch filter, or a twin T passive Notch a

               

            possibility.

               

             

               

            Image result for twin t notch filter

               

             

               

            Again you will have to do the analysis of the filter to establish 60 Hz rejection.

               

             

               

            Of course PSOC 3, 5LP, have DFB block which could be used. Or use MAC in

               

            PSOC 4 to implement an IIR filter.

               

             

               

            Where are you measuring the 60 Hz, at output of OpAmps ? Are you using

               

            scope differentially or single ended ? Former preferred or float the scope.

               

             

               

            www.google.com/url

               

             

               

            Regards, Dana.

            • 3. Re: Yet another frequency measurement question
              un3x

               Hi Dana,

                 

               

                 

              You're amazing, I see you replying everywhere. And always with great information. You've given me some things to look at and consider. For this project, I hope to use the PSoC4 as I intend to embed it in a product for sale. Every $5 spent at design raises MSRP $35~50 and the attractiveness of low price must always be paid attention to. I've got a couple of the PSoC5 -059 kit boards, too, but am trying to resist the urge of using them for this. :) 

                 

               

                 

              Here's my scope hookup and I'll try removing ground,too, to see how that works.

                 

                 

               

                 

              Scope lead is on P1.2 side of the left resistor. Scope ground is on P1.3 side of the right resistor. 

                 

               

                 

               

                 

              I'm going to play around with various analog circuits today to see what I can do with 60Hz and also "see" what the ADC's values are...

                 

               

                 

              Thanks,

                 

              Chris

              • 4. Re: Yet another frequency measurement question
                user_14586677

                You're amazing, I see you replying everywhere. And always with great information.

                   

                 

                   

                Thanks for the compliment, but there are several supporters of the site that train me

                   

                as well.

                   

                 

                   

                I see your R's are 5 percenters, that will lower your CMR drastically, mismatch, so take a look

                   

                at the ap note, or use some of the online tools to help -

                   

                 

                   

                    

                   

                              

                   

                          

                   

                http://www.ti.com/lit/ml/slyb119a/slyb119a.pdf     TI Tools

                   

                http://www.ecircuitcenter.com/Circuits.htm     More Analog Tools

                   

                http://www.johansondielectrics.com/x2y-for-instrumentation-amplifiers.html#.VYMwtUZHQ3A

                   

                http://masteringelectronicsdesign.com/differential-amplifier-output-common-mode-voltage-calculator/     CMR Calc IA

                   

                 

                   

                 

                   

                 

                   

                 

                   

                When you do scope differential measurments be aware that not all scopes

                   

                have good CMR themselves channel to channel when making measurements.

                   

                So consult their specs as well.

                   

                 

                   

                 

                   

                Regards, Dana.

                • 5. Re: Yet another frequency measurement question
                  user_14586677

                  Take a look at this case, using 1% Rs, a CM Vin of .1 V, look at

                     

                  the output CM V, its awful.

                     

                   

                     

                   

                     

                   

                     

                  .1% R's yields 40 mV of output CM. Note this tool does not take into account

                     

                  Aol differences in the OpAmp causing CMR limitations, the Aol delta can can be 40% or more.

                     

                   

                     

                  Regards, Dana.

                  • 6. Re: Yet another frequency measurement question
                    user_342122993

                     @un3x,

                       

                    Looking on you schematic and photo attached, I think that the microphone is not hooked up properly. The electret mic has opamp inside which needs to be provided some 1.5V thru resistor and AC output has to be decoupled by capacitor - look on the data sheet or online. That OPAMP has already a gain of about 1000, so you may not need another amplification in PSoC.

                       

                    Secondly, if you do need some further amplification, use PGA inside PSoC , do not make differential amplifier.

                       

                    odissey1

                    • 7. Re: Yet another frequency measurement question
                      un3x

                      Thanks odissey1, I found a couple circuits on-line to try out. I'm not the first hobbyist to use these. I attached a PDF printout from EE stackexchange of one circuit I'll try. I sorted through my parts bin and still have a 2n3904 from school 20 years ago. 

                         

                       

                         

                      I'm going to solder 90 degree headers on another -049-42xx board so it stands up and I have better access to the breadboard. 

                         

                       

                         

                      Dana, I measured those two resistors and they are both 987 ohms. Seems I've been in this rodeo before; along with the 3904, I found a 741 IC. Obviously, I won't trust 5% to production, but during R&D, I can hand pick parts to get things just right.

                         

                       

                         

                      Thanks,

                         

                      Chirs

                      • 8. Re: Yet another frequency measurement question
                        user_14586677

                        Here is an interface for the mic you could try using PSOC OpAmp.

                           

                         

                           

                        Regards, Dana.

                        • 9. Re: Yet another frequency measurement question
                          un3x

                          Wow, thanks Dana, that looks like a great design! 

                             

                           

                             

                          I just tried the below circuit with pretty good result, other than 800 hz spikes that come from nowhere:

                             

                             

                           

                             

                          Oh, and yeah, those are the same 800Hz spikes on the scope above. They didn't seem as obnoxious then as they are now. The above circuit I credit to Stack Exchange EE site. Instead of aiming for a 20 Hz low fc, I'm shooting for 50~60 Hz. And if I can figure it out, I'll shoot for a fc high of some thing under 800 Hz. Heck, I wouldn't care if it was 200 Hz.

                             

                           

                             

                          I'll work on that circuit next... Once the O'scope shows data I like, I'll work on reading the ADC values...

                             

                           

                             

                          Thanks,

                             

                          Chris

                          • 10. Re: Yet another frequency measurement question
                            un3x

                             Hi Dana,

                               

                            I tried that Texas Instruments circuit and I believe it doesn't have enough gain for the ADC to measure frequency, I'm measuring only about 100mV p-p. I'll take tomorrow away from circuits and get back on it Monday.

                            • 11. Re: Yet another frequency measurement question
                              un3x

                               OK I'm going to try the PSoC5 and see what that gets me. If it requires little or no discreet components, then the labor savings is worth "twice the price". Having seen what PSoC4 delivers, what new special magic is in the 5 that I can take advantage of? I have seen PGAs can implement OpAmps, so there's already a bonus: more OpAmps.

                                 

                               

                                 

                              Thanks,

                                 

                              Chris

                              • 12. Re: Yet another frequency measurement question
                                user_14586677

                                Brief overview -

                                   

                                 

                                   

                                    

                                   

                                          

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

                                PSoC 1

                                PSoC 3

                                PSoC 4

                                PSoC 5

                                8-bit M8C core

                                8-bit 8051 core (single-cycle)

                                32-bit ARM Cortex-M0

                                32-bit ARM Cortex-M3

                                up to 24 MHz, 4 MIPS

                                up to 67 MHz, 33 MIPS

                                up to 48 MHz, 0.9 DMIPS/MHz

                                up to 67 MHz, 84 MIPS

                                Flash: 4 KB to 32 KB

                                Flash: 8 KB to 64 KB

                                Flash: 16 KB to 32 KB

                                Flash: 32 KB to 256 KB

                                SRAM: 256 bytes to 2 KB

                                SRAM: 3 KB to 8 KB

                                SRAM: 2 KB to 4 KB

                                SRAM: 8 KB to 64 KB

                                8 x 8 MAC

                                24 bit Digital Filter Block

                                32 x 32 single cycle

                                24 bit Digital Filter Block

                                Switch Cap Filters, BP, LP, HP…DTMF generation

                                 

                                 

                                 

                                I²C, SPI, UART, One Wire, LIN, FS USB 2.0, Powerline

                                I²C, SPI, UART, LIN, FS USB 2.0, I²S, CAN

                                I²C, SPI, UART

                                I²C, SPI, UART, LIN, FS USB 2.0, I²S

                                 

                                 DMA

                                Up to 16 UDBs

                                DMA (4M Series)

                                 DMA

                                Up to 16 UDBs

                                1 Delta-Sigma ADC (6 to 14-bit), 131 ksps @ 8-bit, also SAR

                                1 Delta-Sigma ADC (8 to 20-bit), 192 ksps @12-bit

                                1 SAR ADC (12-bit), 1 Msps @ 12-bit;

                                1 Delta-Sigma ADC (8 to 20-bit), 192 ksps @12-bit, 2 SAR ADCs (12-bit) 1 Msps @ 12-bit;

                                Up to four DACs (6 to 9-bit)

                                Up to four DACs (8-bit)

                                Up to two DACs (7 to 8-bit)

                                Up to four DACs (8-bit)

                                Up to 64 I/O

                                Up to 72 I/O

                                Up to 36 I/O

                                Up to 72 I/O

                                Operation: 1.7 V to 5.25 V

                                Operation: 0.5 V to 5.5 V

                                Operation: 1.71 V to 5.5 V

                                Operation: 2.7 V to 5.5 V

                                Active: 2 mA, Sleep: 3 μA, Hibernate: ?

                                Active: 1.2 mA, Sleep: 1 μA, Hibernate: 200 nA

                                Active: 1.6 mA, Sleep: 1.3 μA, Hibernate: 150 nA

                                Active: 2 mA, Sleep: 2 μA, Hibernate: 300 nA

                                Requires ICE Cube and FlexPods

                                 

                                On-chip SWD, Debug

                                On-chip JTAG, SWD, SWV, Debug, Trace

                                 

                                CY8CKIT-001 Development Kit

                                CY8CKIT-001 Development Kit

                                CY8CKIT-040 Pioneer Kit

                                CY8CKIT-001 Development Kit

                                CY8CKIT-030 Development Kit

                                CY8CKIT-042 Pioneer Kit

                                CY8CKIT-050 Development Kit

                                 

                                CY8CKIT-049 Prototype Kit

                                 

                                 

                                 

                                 

                                 

                                   

                                 

                                   

                                 

                                   

                                Regards, Dana.

                                • 13. Re: Yet another frequency measurement question
                                  user_14586677

                                  The M series, just out, has DMA, 4 OpAmps.....

                                     

                                   

                                     

                                   

                                  • 14. Re: Yet another frequency measurement question
                                    un3x

                                    OK, I lied. I worked on the circuit. I need to travel tomorrow, so I spent tonight on it... 

                                       

                                     

                                       

                                    I found a bandpass circuit on wiki (the very bottom of page, just hit end) that I made some tweaks to:

                                       

                                       

                                     

                                       

                                     

                                       

                                    Which then seems to simulate exactly to what I'm looking for:

                                       

                                       

                                     

                                       

                                    And then I implemented with the PSoC4 on OpAmp 0 and the output pretty much just stays on 5V.....   Any suggestions?  I'm calling it a night. 

                                       

                                     

                                       

                                    Thanks!

                                       

                                    Chris

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