I’ve made a small change in my exposure meter design. Rather than using one set of buttons to increase or decrease the shutter speed or aperture, I’m going to use one rotary encoder for each. I realized, as I was going to make a menu system for changing the ISO, shutter speed or aperture mode and perhaps one or two other items, that I really had no idea what I was doing. I found a few different menu setups for Arduino on forums and other places, but I didn’t really understand them because I don’t have enough experience. I thought it would be better to not use elements I don’t have a firm grasp on.
So instead, I’m going to use one rotary encoder each for changing the ISO, shutter speed and aperture. The encoders also have a built-in button, so I might use that to trigger the reading of the light sensor. I might also use a separate button for that. I haven’t decided yet. Either way, having a separate device to manipulate each variable should make the coding simpler.
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 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.
Today I took a trip to Lime Rock Park in Connecticut for their annual Sunday in the park car show. I suppose it’s actually called a concours d’elegance, but to me it’s just a big car show with a few extra-fancy cars. Every labor day they make a whole long weekend of events featuring classic, vintage and antique cars at the track, with racing on Friday, Saturday and Monday. Racing is not allowed at Lime Rock on Sundays, so they have a huge car show, with cars lined up all around the track.
The highlight this year were the 50 or so pre-war Bugattis. They’re not really my kind of car, but it is really neat to be able to walk right up to these cars, which are probably one of only a handful of their type in the world and are worth millions of dollars.
Anyways, here are the decent pictures I was able to take. It’s tough getting a nice picture of a car at an event where there are thousands of people milling about. The cars were a little more spread out than they are at the Hemmings events, so that was nice. The pictures are in a Flickr album, so if buttons to scroll through don’t show up, just click the image to see everything on Flickr.
I placed the order for all the parts I should need to create my exposure meter. Most of the parts are coming from Adafruit, and most of the supplies are coming from Amazon. The total bill was around $170, but I had to buy some supplies and tools that will be available for use on future projects.
The main parts in this build are an Adafruit Mini Metro, TSL2591 light sensor and a monochrome OLED display. The Mini Metro is an Arduino-compatible microcontroller. It’ll take inputs from buttons and the light sensor, interpret them, and then show the results on the display. The light sensor will give me my light reading in lux, which I can then plug into a formula to solve for either the correct aperture or shutter speed. The OLED display should be pretty easy to read in a bright area. Plus I’ve wanted to use one in a project for a while. Other parts coming aboard are three buttons, an on/off button and some 9 volt battery connectors.
I had to buy some supplies for this, because it’s been quite a while since I’ve build something. I needed more hook-up wire, jumper wires, and breadboards. I also got some jumper wire pins, wire housings and special crimpers to put them together so I’ll end up with a more elegant package of wires at the end.
The Amazon stuff should be in on Monday they say. The Adafruit things don’t have an estimate, but I’d imagine they’d be in by Wednesday because they’re only traveling from New York City. Hopefully next weekend I’ll have a working prototype done on the breadboard.