The evolution of the Boba Fett Range Finder prop continues with the introduction of the Mk3 design. Building on the success and feedback from the Mk2, the Mk3 brings a significant change in the accelerometer integration, aiming for a more streamlined and efficient design.
Integrated Accelerometer: A Leap Forward
The most notable change in the Mk3 design is the integration of the accelerometer directly onto the main circuit board. This eliminates the need for soldering two separate circuits together, as was the case with the Mk2. The decision to integrate was driven by both cost and design efficiency. Two years ago, the cost of soldering the accelerometer chip to the main board was prohibitively expensive compared to purchasing breakout boards. However, the tables have turned, and direct integration has now become the more cost-effective option.
Facing the Challenge: 180° Rotation
The transition to an integrated design wasn’t without its challenges. My board fabricator can only assemble one sided boards. So the accelerometer had to be mounted facing 180 degrees from its previous position, moving to the top side of the board. This change in orientation meant that the voltages, were now different / reversed in the new setup.
Simplifying the Logic with Analog Components
Just as with the Mk2, the key to the Mk3’s low power and simplicity lies in its analog design. Using analog accelerometers that output a voltage level corresponding to their position, we can avoid the need for microcontrollers and complex polling mechanisms. The logic remains straightforward: when the accelerometer is in the active position, the comparator outputs HIGH, and when in the inactive position, it outputs LOW. The change in orientation simply required swapping the inverting and non-inverting inputs to the comparator.
An unintended benefit of this integration is slightly improved battery life. I estimate a 50nA savings, which is a tiny amount, but when idle (LEDs Off) this adds up to over 100 hours of extra battery life over weeks of use.
Lastly, the Mk3 features the same an on/off switch, allowing you to use a single battery for numerous cosplay adventures.
You can purchase my Range Finder on etsy: https://www.etsy.com/shop/WestabyElectronics