3 Replies Latest reply on Jul 14, 2016 12:14 AM by tringwebdesign

    Cirrus Logic Audio Input problem


      My project is to build a seismometer and record ground vibrations. I have bought one of these:




      Which is really nice for £30. It has two wires coming off the copper coil at the base. I've then gone and got the Cirrus Logic audio card which is working as I can record audio from a headset/boom combo through the black headset input.


      What I cannot figure out is how to connect up the two wires coming off the seismometer to get the signal it outputs into the cirrus logic card via either the black mic or pink line-in with Micbias? As the slinky is a Geophone (basically a reverse speaker), I am assuming it's output is mono.


      I have managed to record it on my laptop, by connecting the two wires onto the L & R of a stripped 3.5mm stereo jack and into my laptop, via a 4-pin audio adaptor (as the lappy has a combined 3.5mm audio port) for audacity to record, but this doesn't work with the Cirrus Logic.


      I suspect it's my ineptitude with understanding the 3.5mm audio jack specification. Any help would be appreciated.



        • Re: Cirrus Logic Audio Input problem

          So I did some fiddling around with some bought 3.5mm jacks, and seemingly lost the ability to record anything off the geophone. This looks like my problem: https://www.gearslutz.com/board/10447535-post2.html


          If I pull out the 4 pole 3.5mm connector from the laptop slightly i can record from the slinky. It picks up the TV volume, and a loud exhaust going past the house.


          Any ideas on how to wire this up permanently?

            • Re: Cirrus Logic Audio Input problem

              I haven't used the headphone/MIC input myself yet, but according to the user manual that's a 4-pole TRRS input with GND on the second ring (counted from the tip) and MIC on the sleeve (tip and first ring are L/R headphone outputs).


              Connecting the seismometer to the second ring and sleeve could work.


              If the output is strong enough you could also use the line input. Hook up one wire to the sleeve and the other one to both tip and ring (so you get the same signal both on left and right channels).


              so long,



                • Re: Cirrus Logic Audio Input problem

                  Thanks Matthias, i'll give it a go. The slinky appears to be strong enough - picking up things like a conversation on the phone and me coughing in the same room as it. Below image is a 40ft artic-lorry trying to get into a turning which is about 15m from the device - he didn't make it. Interestingly Audacity appears to be able to record at frequencies lower than what the soundcard can handle (on my laptop - 8000hz) - must be some software processing going on there.


                  All I need to do now I suppose is work out how to compare the waveforms coming off the slinky with other known waveforms so I can get a frame of reference as to what these vibrations actually mean in the real world. I would like to be able to get the slinky into our garden shed that has a concrete base with the rpi powered on batteries. The shed is about 25m away from the road and if the slinky is sensitive enough, as it appears to be, it should be a good location for it.