First, I am a novice to the field of electronics and micro-controllers, started just 3 weeks ago, with an aspiration to make some devices for my field data collection. Here is what I created - an ultrasonic wave recorder. I shall mount the SONAR [ping))] sensor from a fixed platform having it pinging downward on the water surface and measure instantaneous change in distance (at about 8-10Hz) and write the data on a microSD card. Here is an early picture of what I have wired on a breadboard. After this picture I have included 3 LEDs to indicate Error (Stay Red), SD OK (Stay Green) and 'data logging in progress' (Blinking Amber). I have also included an LM35 digital temperature sensor and record its data, so that I can apply more accurate calculations of the speed of sound at the time of data acquisition. Hence I am recording one-way travel time in microseconds as well. Now I am working on a switch which will Start/Stop data logging. And then I will work on the battery issue. The second picture is a snapshot of the data captured by the device.
I hope to write a full step-by-step instructable once I am done, all credits with link, and the complete Arduino sketch will accompany at that time. I am so excited that I cannot help not sharing a picture now :p Pardon my excitement!