Final Design

Figure 1: Modified digital caliper with grips and transducers in sleeves along with electronics housing.

The final design of this device consists of a modified digital caliper with a separate electronics box containing a numeric display. The modified calipers have a pair of 3D printed sleeves on the caliper arms that house the required ultrasonic transducers. The back side of the calipers contain a set of 3D printed finger grips for comfortable holding and ease of use of the device. The separate electronics box houses the PCB and microcontroller that, in conjunction, perform the speed calculation which is then displayed on the attached LCD screen.

The caliper sleeves were designed using the modeling software SolidWorks and were prototyped with a Makerbot 3D printer before final production on the Objet Connex 3D printer. The Makerbot was chosen for the initial phase due to its inexpensive material and user-friendly software while the Connex has the ability to produce the varying materials and stiffnesses necessary for the final design. TangoBlack, the softest material available on the Connex, was used for the transducer housing to allow for user comfort when taking readings. It also had the added benefit of quick and easy insertion and removal of the transducers from the device. Vero Clear, the stiffest material available on the Connex, was used for attachment of the sleeve to the caliper itself.

The caliper sleeve design includes slots for 4-40 hex nuts, to ensure contact with the caliper itself and thus provides a firmer attachment. Additionally, a clipping mechanism was added to constrain any vertical movement as well as holes for set screws to prevent any undesired lateral movement. Lastly, cable clips were added underneath the caliper sleeve to keep the transducer cables secured. The final design of the sleeves with all the aforementioned components can be seen below in Figure 2.

Figure 2: Caliper sleeve designed to house the transducers.

The finger grips were designed to add comfortability to the design during usage. They utilize the same materials as the transducer sleeves in order to achieve the same secure attachment to the caliper while also providing optimal comfort to the user. During operation, the user will use a chosen finger (typically the index or middle finger) as well as their thumb to open and close the caliper across the breast and obtain speed measurements. In order to secure the fingers to the grips, a velcro strap has been added to ensure proper control of the device.

Figure 3: Caliper grips used to open and close the calipers

The electronics housing was designed as a means to keep the electrical components of the design safe and avoid damage. The housing itself consists of an opening to which the LCD screen display is attached, inner shelves for the PCB and microcontroller, a fan duct for cooling of the PCB, and a removable door for easy access to the PCB and microcontroller. Additionally, cable holes in the housing allow for complete operation of the device while the electronics are kept safe.

Figure 4: Housing unit to host electronic components.

The PCB was designed as a means to obtain data from both the caliper and transducers independently. For the calipers, the circuit amplifies the 1.5 volt logic level of the calipers to a 5 volt logic level for compatibility with the microcontroller and data processing. For the transducers, the circuit pulses and receives a signal from the transducers to obtain a time of flight data that is also sent to the microcontroller.

A Parallax Propeller microcontroller, provided by the sponsor, then performs the speed calculation from the caliper’s distance and transducer’s speed data. Later, the controller outputs this sound speed to the numeric display on the housing to be interpreted as abnormal or normal.