Assistive Rangefinder
Materials: ultrasonic sensor, vibrator, Pro Trinket, Li-ion battery
Tools: Arduino, 3D printing, Premiere Pro
Time: 5 days
The Decisive
I love street photography, and street photography is all about capturing the decisive moment. Since my camera doesn't have the auto-focus function, it's quite challenging for me to take the decisive capture-moment through manually focusing, which often leads to missing the best timing. I wanted to build a tool that could intuitively inform me of the correct focus distance, so I would be able to save time on manually focusing.
A Rangefinder with Haptic Feedback
This camera-mounted rangefinder generates subtle vibration when the subject is within its designated focus distance (+/-100mm) set by the user.
Initial Prototype
The first circuit was a combination of an ultrasonic distance sensor, an LCD screen, and a potentiometer.
Considering the real use-case scenario, which is going to be mounted on the camera, I decided to go for a smaller design. I updated the following components:

1. Replaced Arduino Uno with Adafruit Pro Trinket - 3V 12MHz, reducing 80% of the circuit board size.

2. Switched the distance sensor to Maxbotix Ultrasonic Rangefinder - HRLV-EZ4, reducing 50% of the previous sensor.

3. Added the vibrator motor for haptic feedback.

4. Added the rechargeable Li-ion battery for portability.

5. Eliminated the LCD screen.
Final Design
I included the Adafruit LiIon Backpack Add-On for Pro Trinket for charging the battery through USB port from directly Pro Trinket board, which enables charging without detaching the JST cable and taking out the battery.
See the Arduino code >
3D printing Enclosure
I designed and iterated the enclosure for 3 times until it was fitted with the electrical components very well.
Test Flight
Shot with Assistive Rangefinder
I took these pictures during Emerald City Comic Con 2018 with the assistive rangefinder mounted on my camera.
ISO 200, Shutter 1/500s, 35mm f/2
ISO 320, Shutter 1/500s, 21mm f/4
What I've learned
1. Soldering become very hard when there are no clamps for holding two wire ends.

2. Always do a test flight before finalizing the design.

3. There is a trade-off between numbers of functions and size.

4. Always have a backup or plan B.
Let's go out and 📷 !