Update on the exposure meter

The parts for the exposure meter came in last week. It seems that everything works just fine, except for the breadboard I picked out of the pack of 3 I ordered. It seems like the lower half of it does not work. Hopefully the other two are better.

Anyways, these are the major parts in the system:

  • Adafruit Mini Metro. This is an Arduino-compatible, ATmega328-based microcontroller. It’s the brain that processes the input from buttons and the light sensor and displays everything on the display.
  • 128×64 OLED display. This seemed like a good choice for this project because the OLED displays are easy to read in bright light, and I’ll be using this thing outside most of the time.
  • TSL2591 light sensor. This senses the light and gives the microcontroller somewhere to start when deciding what shutter speed or aperture to suggest.

So far, I have a set up that does the following:

  • Reads the light sensor and returns a value in lux.
  • Plugs the lux reading into an equation to get an exposure value.
  • Plugs that exposure value into one of two equations:
    • One equation finds a shutter speed that works with a selected aperture.
    • The other equation finds an aperture that works with a selected shutter speed.
  • Sends the lux reading, exposure value, selected ISO, and the computed shutter speed or aperture to the display.

Now I need to create a menu system for adjusting a few settings, such as the ISO, changing the mode from shutter speed to aperture and perhaps setting a minimum shutter speed or aperture value. I also need to come up with a way for the results from these equations to get rounded to the nearest third of a stop so they’re easier to use. That might be the trickiest part, but I guess I’ll come up with something.

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