8 Replies Latest reply on Feb 26, 2015 2:15 PM by user_14586677

    Send ECG signal with BLE

    manuel.martinez.lb13505

      Hi everybody!!

         

      I have bought my PIONEER kit. I'm developing a project about Electrocardiogram (ECG). I would like to measure the electrical signal of heart, then digitize and send it with the BLE kit an other device.

         

      I need to create a custom profile that be able to send data string to other device (Smartphone). I would like to know if someone created a custom profile to send data string.

         

      My idea is create a buffer that containing the sampled signals and then send them, with each interval connection established over the master.

         

      Thanks for your support.

         

      Manuel Martinez[PY]

        • 1. Re: Send ECG signal with BLE
          user_14586677

          If you search "custom profile" there are several threads here where folks

             

          have uploaded basic projects moving data.

             

           

             

          Regards, Dana.

          • 2. Re: Send ECG signal with BLE
            user_78878863

            Just define the custom service as you need it. In your code, set the attribute value for your custom attribute when the buffer got filled (and handle notifications). If the other side of your connection has enabled the notifications, it gets the data. Otherwise it must read the data explicitely.

               

            Note that BLE is not designed to transmit a continuous data stream, bute just attributes that don't change that often.

            • 3. Re: Send ECG signal with BLE
              rohit.kumar

               manumart,

                 

               

                 

              You can use the project at http://www.cypress.com/?rID=107617&cache=0 as a reference to create Custom profile and use it to send the data.

                 

               

                 

              I do have a question. As the measurement is Heart rate data, why don't you use the Standard BLE HRS service? This way, you will not need a custom App to make sense of data over Custom Service. Standard services are understood universally.

                 

               

                 

              -Roit

              • 4. Re: Send ECG signal with BLE
                manuel.martinez.lb13505

                 Thank you for your supports!

                   

                 

                   

                ROIT, I want not measure the heart rate, I would like measure the electrical signal of heart to then transmit the data stream and plot the signal in my cell phone! Attached the graphic.

                   

                 

                   

                I have been reading about the time that it take transmit a packet from the sender [about 7.5ms(interval connection time minimum) + 1.25ms(time for next connection interval)] to the receiver and the payload size for each packet transmited (about 30 bytes) from link layer.

                   

                 

                   

                Could I send data stream of 30 bytes each 10 ms, trying to graph the ECG signal in real time in the receiver?

                   

                 

                   

                I'll read all the advice that sent me and I'll try to make my custom profile!

                   

                 

                   

                Manuel Martinez[PY]

                • 5. Re: Send ECG signal with BLE
                  rohit.kumar

                   30 bytes per 10 ms is possible. You can set the appropriate connection interval (10 ms) by sending a connection parameter update request to the connected Client device. Also, set the custom characteristic data size and MTU size as 30 bytes.

                  • 6. Re: Send ECG signal with BLE
                    user_14586677

                    How many bytes / graph frame. Seems like you are hovering around

                       

                    the flicker frame rate human eye can see. Maybe best approach is

                       

                    to buffer an entire frame before presenting on display, even then that

                       

                    will be close to observable flicker updatre rate.

                       

                     

                       

                    If heart rates quite low then a smooth painting in time the data only

                       

                    alternative ?

                       

                     

                       

                    Regards, Dana.

                    • 7. Re: Send ECG signal with BLE
                      user_78878863

                      You really need to use the notificatzion mechanism of BLE. That way the PSoC4 can push updates, and there is no problem with the phone maybe requesting data to early in the 10ms cycle. You can also try larger package sizes so you don't need to transmit so often.

                         

                      I think the largest payload for a single packet is 20bytes, so it might be a good idea to transmit multiples of that.

                         

                      On the display side, it should be OK to update only the portion of the signal that gets updates data. That way no flickering should occur (since th other parts are never redrawn)

                      • 8. Re: Send ECG signal with BLE
                        user_14586677

                        One approach is to keep a buffer of the signal, say a buffer of amplitudes vs time.

                           

                        Then when new data comes compare each element of the data with buffer, if data

                           

                        changed update that element in buffer and change that portion of display. If no

                           

                        change NOP. That will produce the cleanest display appearance of all approaches.

                           

                         

                           

                        Regards, Dana.