With a midterm deadline looming, I need to have the entire design defined in every way so it can be signed off and finalised. This means tackling problems I'd happily put off indefinitely. The camera is split up into 3 main sections: the sensor and lens within the right hand diameter, the dials and controls within the left hand diameter, and the battery and SD card down the centre. Having started to build the CAD model, it came time to figure out how the dials would work and interact with the rest of the internals. The dials and all related components need to fit in the gaping hole (and corner deadspace) in the part built model shown below:
I am a product designer and certainly not an electronic engineer. In fact, having been on the product design track since I started secondary school, I have never been taught anything about electronics. All I know is general knowledge I have picked up over time messing with and rebuilding computers and servers, and playing about with reverse engineering and my own little Raspberry Pi. Given my limited knowledge then I didn't know what sort of component I could use to read the position of my dials.
Conventional dials are built upon a component with a central shaft, such as a potentiometer. However, the dials in this design have a gaping hole through them, so there is no centre available. This forced me to investigate ring shaped fitting which could potentially fit within the setting ring itself. It took me most of the day to figure out what to use. I looked at many things which seemingly looked perfect. The screenshot above shows ring encoders which can read the position of a spinning ring. Most of the ones shown are magnetic, but some are optical. This would have been perfect... were they not exclusively designed to be fitted onto industrial machines (CNC C-axis, automation, robotic arms, steering racks etc). While a perfect solution, there just weren't any small consumer electronics friendly versions out there on the market.
After this then I continues looking for other ring encoders. Panasonic and JPT sell encoders like shown above, at the correct diameters for my project, but much too high! These encoders are designed for automotive consoles with things like air conditioning dials. Again, no consumer electronic versions were available. Not really knowing what I was looking for, I ended up going back and forth all day covering components such as: potentiometers, jog dials, ring type encoders, magnetic and optical encoders, edge drive jog wheels, rotary encoders etc. Eventually I decided to use this:
The component shown above is a vertical type hollow shaft micro rotary encoder, sourced from RS Components (see link). As an encoder, it will read the position of the shaft and tell the controller how much it has rotated. After realising there was just nothing which would fit around the inside of the setting rings, I chose to use the smallest flat mount encoder I could find, and chose to have it cog driven off of the setting ring. The idea is that when the main dial spins, it will drive the cog, turning the shaft in the encoder, and producing a readable signal which can then determine where the dial has been turned to.
There is very little space to fit anything around the dials. There is a tiny bit of corner dead space which was the only available area where I could potentially cram this component. Even with the smallest one I could find, it still protrudes into the profile of the dial. You can see how little space is available below:
Below we can see how I chose to arrange the encoders around the ring. I had to ensure enough circuit board space for the component to be realistically mounted and soldered without becoming impracticable. The centre of the shaft is along the 45 degree angle line from the centre of the setting ring. Due to the height of the encoder and the cog which needed to be mounted on top of it, the cog would actually sit too high to be driven off the bottom dial (there are two back to back, aperture speed front, shutter speed back). This meant that the encoders has to be driven off the dial on the opposite side. This meant that one of the encoders needed to be mounted on a break out board in a mirrored fashion (the top one in the case below, you can see it just slightly greyed out behind the break out board).
With a breakout board required, I blindly modelled up a solution without thinking about how the board would connect. I decided to use a ribbon cable, only to find that, having placed the break out board at the top rather than the bottom, the greater space taken up by the mount for the SD card slot meant that there wasn't actually enough space for a ribbon cable to be fed down. Eventually I reversed the design, so the break out board was at the bottom, with the encoder reading the back dial, with the other encoder being mounted on the main circuit board so it could read the front dial, as shown below:
To get an idea of how the encoders are driven, below is a render with the cogs in place. These cogs are floating in this image, but will be fixed to the inside of the dials once the CAD model is complete. Now I need to figure out how the actual exterior shell of the dial will fit onto the model, attach to the cogs, spin freely and essentially, not fall out!
