The Raspberry Pi has been a revolution in allowing people to run cheap computational experiments. I wanted to see if I could put together my own experiment: a seismic monitoring station.
You might be asking why would I want to do this when Britain hardly ever gets any significant seismic activity. With a suitably calibrated device, seismic vibrations from around the earth can be sensed and logged.
I have a different plan for my seismic monitor, I wanted to see if I could detect and log traffic vibrations – living in an old house next to what feels like a relatively busy minor country road – what effect do all the lorries have on our property?
To this end I purchased the cheapest seismic sensor I could find. It’s a Slinky Seismometer System and yes, it uses a mini-slinky. This device is from a family of seismic sensors called Geophones which are traditionally used to detect more local vibrations, perfect for my application.
The slinky comes in kit form and is very well made with laser cut acrylic pieces, strong magnets, coil of wire and slinky all included. Building it took all of about 15 minutes. It stands about 50 cm high and the perspex cylinder is about 15 cm diameter. Two wires come off the base of the unit from the coil so when the slinky detects movement a signal is sent through these wires.
To actually do something useful with this signal it needs to be recorded and to do this with a Raspberry Pi I need an Analog to Digital Converter (ADC). This in essence means a soundcard that can record from a microphone or line input.
Unfortunatly for the Pi it’s audio input options are non-existent, therefore an add-on card was purchased in the form of a Cirrus Logic Audio Card which connects directly to the Pi’s GPIO.
This card has all the inputs for recording audio signals and from research has some high quality components. It is however berated by the rPi community for the manufacturers lack of software support and it required a bit of manual work to get it to work, luckily someone has found the solution to it’s lack of software support. Once installed, some testing through the mic input with a headset microphone using arecord proved it was able to record audio signals.
Testing the Geophone, by plugging it into a laptop via a 3.5mm TRS connector and recording sound via Audacity by creating movement in the room showed the Geophone was indeed detecting vibrations. Image below is me tapping on the floor right next to the slinky.
Next: Getting the Geophone connected to the Cirrus sound card. At this point I am marking this project as on-going as I can’t seem to fathom out how to get the slinky attached to the soundcard. I’m asking the community for help, as electronics isn’t my strong point.
If you are interested in the sort of traffic I am hoping to record from this device, here’s a recent photo of some of the huge lorries that come down our road… and yes, it’s at a funny angle (because it’s too big for the road).