Arduino is a platform which lends itself well to data logging, at least when its relatively small internal memory is enhanced with the inclusion of external storage for the data so logged. When building a device that will sit by itself gathering data, though, power draw becomes a concern, and saving micro-amps becomes the watchword - which is where Edward Mallon's latest data-logger design comes in.
Built as part of his work with the Cave Pearl Project, which we covered late last year as part of our overview of Arduino-based flood monitoring systems, Edward's data logger is designed around the compact Arduino Pro Mini. It's a tweak of a previous design, modified for simplicity: at around two and a half hours, Edward has measured the build time as being a third lower than the design it replaces.
It's possible to follow Edward's build entirely step-by-step to end up with your own data logger, but taking the time to read through as a study rather than a tutorial unveils plenty of interesting techniques for improving the longevity of the battery-powered device. Tricks like removing the resistors through which power flows to status LEDs on the Arduino Pro Mini, real time clock (RTC) module, and the external pull-up resistor from the micro-SD card module all help to drop the power drain down to the point where the system can run for around six months on three AA batteries, based on a 15-minute duty cycle.
Its been almost a year since the last stand-alone logger tutorial, and I continue to receive questions from people adopting the platform in education settings. That feedback makes it pretty clear that soldering is the biggest stumbling block for beginners, so I have reconfigured the promini build to use pre-made DuPont style jumper cables wherever possible. The basic wiring diagram is unchanged, but I use a different SD card adapter and changed resistor locations to reduce component prep and make the overall assembly easier.