required hardware

• OV528 camera module
• mbed board with an SD card slot (I used NXP K64F) or an SD card shield for boards without an onboard SD card slot
• micro SD card

mbed-timelapse

This application takes a photo every 10 minutes and stores the images on an SD card. The application will also save a text file log to the SD card. The application utilized the mbed OS filesystem to store the photos and log.

I let my timelapse run for two weeks. This introduced some interesting requirements:

• Logging - When running in the short term, I relied on capturing STDOUT from the board with a serial connection to my computer. As the device was going to be running without any PC connection, I needed a way to check that the application was still working as intended. I used a logging function to write any messages to a file, which I could view later on the SD card.
• Continuous naming scheme - To make the timelapse, I would need to know the order in which photos were taken. Without a persistent RTC, I relied on a naming scheme. So, they'd need to be named in order. I chose img0, img1...imgN. However, between power cycles, the device would lose this count. I chose to make a new directory with each power cycle, such that they would be named dir0, dir1...dirN. When the application starts, it finds the first dirX that does not exist and creates it. Within each of these directories, images were named according to img0, img1...imgN, using a global count variable to keep track of the image number.