Tatum Robotics.
Tatum Robotics is a young start-up engineering company aiming to offer people with deafblindness, a historically underserved community, their first independent communication tool. While Tatum Robotics has developed their own first prototype, they are simultaneously seeking to expand their technology to tackle another problem in the deafblind community: safety in managing visitors or packages in their homes.
Through Generate Product Development Studio, I worked with a team of engineers to design a vibrating bracelet capable of connecting to an outdoor ‘doorbell’ via bluetooth.
Requirements
Wearable Bracelet / Module:
Bluetooth Low Energy (LE)
10+ hour battery life
USB-C charging (universal)
Comfortable elastic fabric
Swappable band sizes
Safe, No overheating, Closed system
Vibrates Accordingly
Easy to put on and remove
Two piece assembly (DFM)
During the initial phase of brainstorming and research, the team worked to look into existing wearable technology such as the Apple Watch, the Whoop Band, Fitbits, and regular wristwatches. In parallel, the team also investigated technological systems similar to the one we were trying to develop such as Apple Home, Blink, Ring, and Nest. With this background, we were able to determine what features were successful and why, what types of materials were being used, and how they were manufactured. Little research was collected regarding the cost of alternatives such as pagers, but sufficient information was used to aim for something easily manufacturable and resource efficient (a specific price range was not calculated).
Early in the design cycle, the team realized it would be difficult to develop the wearable technology without development of a doorbell (something designed to communicate with it), so during the re-scoping process, we transitioned from the initial product requirements to our final product requirements:
Doorbell:
Bluetooth Low Energy (LE)
Wall Powered (16V)
Recognizable design
Doorbell ‘visitor’ button
Doorbell passcode buttons
Labeled Braille
Responsive LED (RGB)
System Overview
Using iterative prototyping and extensive user testing, we developed a custom Bluetooth enabled doorbell with responsive visual and audio feedback to send differentiated vibration patterns to a wearable no larger than a normal wrist watch. Our end result was a comfortable wearable with a 10+ hour battery life, charged by a universal USB-C. The bracelet has swappable size bands and hypoallergenic elastic fabric for maximal comfort. The bracelet receives differentiated vibration patterns for user recognition. A known visitor will enter their unique code on the three bottom buttons of the doorbell which then sends a distinct vibration pattern to the user, while an unknown visitor presses the large top button of the doorbell to send a different pattern to the user.
Mechanical Design
wearable
Doorbell
Doorbell
The doorbell we created is part of a larger mechanism that involves communication between the doorbell and the module. The doorbell’s intent is to differentiate between an expected and an unexpected visitor at the door of a Deafblind user. Our intent is for visitors who are expected to visit the house (family, friends, caretakers) to be given a code consisting of three numbers that they can input using the three small buttons on the doorbell, after pushing the top larger button to ring the doorbell. Unexpected visitors will not have a code, and wont know that any code is needed and therefore will only press the top larger button. Based on the code input at the doorbell, a differentiating vibration pattern will be sent to the module and it will vibrate accordingly.
Rear Housing: houses the doorbell pcb, LED strip and slot for LED placement, hole in the back for wires to connect to house power
Front Housing: Holds nuts and buttons in place. Displays the Tatum robotics logo and braille for each button signifying the numbers in the code.
Big Button (22 mm): intended to act as a normal doorbell for any user (expected or unexpected to use)
Large Hex Nut (M22): press fit into hex extruded cut in the rear of the front housing and intended to hold large button in place
Small Button (12 mm): three of these small buttons are inserted into the front housing in a vertical orientation and represent numbers one, two and three from top to bottom to receive a code
Small Hex Nut (M12): press fit into hex extruded cuts in the rear of the front housing and intended to hold each of three small buttons in place
LED: emits white light when it's dark outside and otherwise off. Intent is to light up bright green when a correct code is input and red when a wrong code is input.
Acrylic Coverglass: covers the Led and encloses the entire doorbell assembly (attached with small amount of superglue)
Custom PCB: custom made to fit the inner dimensions of the rear housing
Screws and headsets: fixes components together as an assembly
Wearable
Designing a bracelet that uses vibration to alert deaf-blind individuals of visitors at the door requires a careful consideration of mechanical design principles. The general design of the module is simple and sleek, with a strong focus on functionality and ease of use. The module houses the various components of the bracelet, including the vibration motor, PCB, and battery. The vibration motor is positioned in a way that maximizes transmission of vibrations to the wearer's wrist, and the microcontroller is programmed to activate the vibration motor when an alert signal is received from the doorbell. The module is two parts with four threaded M1.2 screws for closure in all four corners; this was a critical design decision as it allowed us to open and close the module easily (without any damage to the housings), but for future designs we considered using snap fits. Additionally the module features spring loaded pins on both sides to secure the band straps. The spring loaded pins act as a modular method to exchange band sizes, materials, and colors.
The slip-on elastic band without this adjustability was ultimately chosen following user testing for its comfortability and simpler user experience. Attachment points were then made external using the watch pins to maximize internal space for other components. Five size options detailed below ensure every user can choose a sufficient fit. Band lengths were chosen based on standard bracelet sizing guidelines, accounting for the width of the module.
The purpose of the band is to enable users to comfortably wear the module on their wrist. It is intended to maintain sufficient contact between the module and user while being easy to put on and remove. A one inch elastic fabric was trimmed with the ends machine-sewn to create attachment loops. Spring bar watch pins are used to attach the two loops to either side of the module. This assembly allows for bands to be fully cut and sewn prior to attachment to the module.
The final band design is available in the following five sizes and their corresponding lengths. This design decision was made so that users may select the best fit for their wrist size and have a “slip-on, slip-off” wearable. Other band designs explored included mechanical clasping mechanisms, magnetic clasps, and a classic watch link design which allowed users to add or remove links to adjust fit. Design iteration was driven by the need for the bracelet to remain a closed circle when being put on or removed to reduce the possibility of the bracelet being dropped and lost. This led to bands which attach at one side of the module and loop through the other side, creating an adjustable system. After abandoning a magnetic closure for this system due to its complexity, a band using a tri-glide slide for adjustment was created. The fabric looped through the buckle and one side of the module such that sliding it in either direction shortened or lengthened the band. The band was initially anchored inside of the module by sliding a dowel pin through the end loops as shown below.
