Improved Beepball

Designers: Emily M. Mugler, Steven E. Reich, and Margaret M. White

Client Coordinator: Kim Lyons

Supervising Professors: Richard Goldberg, Kevin Caves

INTRODUCTION
Beepball is a sport similar to softball, designed for individuals who are visually impaired, where a beeping transmitter inside a 16-inch softball informs players of the ball’s location. The beeping transmitter in current commercial beepballs sometimes fails after a hard hit, and is often difficult for players to hear. A new, more durable Beepball was designed for the Durham team. This ball has two speakers to provide louder sound if the ball lands on one speaker. In addition, the ball charges faster and lasts longer on a charge than commercial models.

SUMMARY OF IMPACT
In initial testing, the new beepball was well liked. The coach of the Durham Beepball team said, “It’s a great ball. I could really tell the difference in the way the players tracked the ball in the field.” Several of the players had positive reactions to the ball, especially the two-speaker design and the slightly higher pitch of the beeping. After one player made a play on the ball, a teammate shouted, “Great play!” to which he responded “Great ball! I really like the way it sounds!”

TECHNICAL DESCRIPTION
The Improved Beepball (Figure 1) comprises a large softball (16″ circumference), which houses a battery, on/off switch, beeping circuit, and speakers.

The beepball uses a 7.4 V rechargeable lithium ion battery, which is compact (2x1x0.6″) and has no “memory,” providing longer battery life. The battery is connected to a 1/8″ audio jack, mounted flush to the surface of the ball, so that the external battery charger can be connected to the battery, which is located inside the ball. The battery charges using a commercial wall-outlet-mounted unit (Universal Smart Charger, Batteryspace.com), which produces 8.4V DC. A switch on the charger allows the user to change the charging voltage, but we fixed this switch in place using epoxy. A red LED on the charger indicates that the battery is charging, and a green LED indicates when charging is complete.

The beeping circuit uses a 556 timer, which functions as two 555 timers in series. The first creates a tone at 1480 Hz. The second turns the tone on and off at 4Hz. The circuit resides on a 2″x1.3″ custom circuit board, designed using ExpressPCB.

To protect the circuitry from large forces, the battery pack and circuit board are encased in a cylinder of polydimethylsiloxane (PDMS), a silicone-based elastomer, which solidifies into a polymer gel after the base and curing agent are mixed together. A metal support for the charger jack, coated in PlastiDip(R) to eliminate electrical shorting, was inserted halfway into the PDMS before it set to help stabilize the jack. Sound permeable fabric is sewn beneath 1″ holes in the leather covering of the ball, so that no potentially damaging materials can enter the speaker chambers.

The circuit board is connected to two separate speaker chambers, 1″ in diameter. The chambers consist of a piezoelectric tweeter (Taiyo Yuden, MODEL #MLS20070), sandwiched between a 1/2″ PVC tube and a 1/4″ PVC tube, sealed with a 1/4″ solid cap at the bottom. The chambers are sealed with epoxy. Cylindrical foam pieces fit around the speaker chamber, and extend the diameter of the chamber to 1 3/8 inches, allowing it to fit snugly inside one core of the ball.

Before we could place this cylinder into the ball, we had to remove a cylindrical portion of cotton from the inside the ball. It is easier to cut this cotton by compression force rather than by pulling, so we created tools out of 6″ sections of steel pipe, sharpened on one end for cutting. A hole drilled through the diameter on the other end allowed a screwdriver to be used as a handle. Creating cores in the ball was quick, precise, and easy using these tools.

To prevent the transmitting device from flying out of the ball after it is hit with a bat, our model uses a cross-member design, with two perpendicular cores of differing diameters through the center of the ball. The battery pack, circuit board and audio jack fit into the larger cylinder, and the two speaker chambers are attached together, in tension, by an elastic cord in the other core. This tension keeps the two speaker chambers together, centered inside the ball.

The charger jack is connected to the oscillator circuit such that when a pin is in the audio jack, the ball does not beep. In this way, the battery charge can be reserved, and the ball silenced, by plugging a blank pin into the ball, and the ball does not beep while charging.

The Improved Beepball achieves a sound pressure level of 95 decibels at 3 inches, equivalent to commercial models. The battery lasts over 14 hours or at least seven times that of other beepballs, and charges in only five minutes. Cost of parts was about $100.

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