Hey guys. I was wondering, could I attach something to my Arduino while it was only powered on by a normal power source (not a pc or a laptop) and have it record data onto something like an SD card, or flash drive? And could I also retrieve the data and then translate it back to normal readable data?
The Sparkfun OpenLog is perfect for that. It logs whatever you decide to Serial.print(). I've used it for months at a time.
The RX on OpenLog is 3.3V only, so if you plan to use it with a 5V Arduino, at the very least, put a 4.7K resistor between TX on the Arduino and RX on the OpenLog. Better, use a 1K:2K voltage divider or a logic level converter.
there is a shield for the UNO.
has RTC, SD card slot and plugs into the UNO.
you remove the SD card.
if there is local power and WiFi, an ESP or one of the new NANO boards with WiFi, can send your data to the net so you can check on it at any time.
What you are talking about is very common - data logging to an SD card. You are may need a RTC to go with it. You can winkle out the card to read it, or you can leave it in there and dump the data to laptop or phone via Bluetooth.