Counter for the Visually and Mobility Impaired

Designers: Larry Sandell, Erin Sparnon
Client Coordinators: Antonia Pedroza, Judy Stroupe
Supervising Professor: Dr. Larry N. Bohs

Orange Enterprises (Hillsborough, NC) is a non-profit corporation employing adults with mental and physical disabilities to perform tasks such as counting objects for shipping and assembly.  The current counting aid is too small to be operated easily or independently by many employees.  The goal of this project was to provide 5 digital counting aids that would be easy to increment, read, and reset.  Specific objectives were to build discrete, durable, portable, safe and rechargeable counting devices.  A counting unit was designed that included a large LED display for the count, a large ergonomic button to increment the count, an input jack for external switches, and a small enclosure.  The design also supports a rechargeable battery source. Five units were assembled and delivered to the client.

How this project helped
The counters have increased the number of employees able to perform tasks and increased the productivity of some employees.  Employees with poor vision and limited manual strength and dexterity can use the counting aids because they are easy to read and increment. Because the devices can be reset independently, they allow employees to perform more counting tasks per work day, since employees do not need to wait for a work coach to reset their counting aids before starting the next task.  Antonia Pedroza, one of the client coordinators remarked, “The students seemed determined to make the products as user-friendly as possible. I was very impressed with the durability and weight of the [counters] because it was something I asked for specifically”.

A photograph of one of the counters is shown in Figure 1. We utilized commercially available enclosures for the counters to save machine and assembly time. The enclosure is made of aluminum with an angled display face.  We machined five enclosures and each can accommodate buttons, switches, jacks and the LED display.  The edges of the enclosures were filed to remove sharp edges, the exteriors were coated with protective Plasti-Dip, and rubber feet were added to increase traction and durability.

The LED display, which consists three 1.5″ digits, rests on the 60-degree sloped panel of the counter housing. The red increment button is mounted middle of the top of the device, and the two black reset buttons protrude from the middle of each side. The increment button can be actuated with very little force applied at many angles, and has a long mechanical life (5 million cycles). The reset buttons also require little force to actuate, but must be held on for about 3 seconds to prevent accidental resetting.

The back of the device contains an on/off switch, an external input jack and a battery recharger jack.  The on-off switch is a two inch tall rocker switch, and the external input jack is a small metal jack that accepts one-eighth inch male plugs.  This jack allows any desired switch to be used to increment the counter. The LED display is protected from the exterior by Lucite and backed by a nylon panel.  This panel is secured by bolts connecting to the enclosure on both sides of the LED display, and supports the circuit board via standoffs.  The battery pack is also well secured, immobilized by nylon ties bolted to the enclosure’s base.

The electronic circuitry (see Figure 2) is based on a counter chip (MM74C925) that receives input from the increment and reset buttons and displays the current count by driving an LED display that is quickly lit digit-by-digit to save power consumption.  A seven-segment display with one and one-half inch digits, which uses low-power LEDs to backlight each segment, provides a large display while saving battery life. The common anode LED display interfaces to the counter chip, a common cathode display, by inverting the driver output with NPN transistors.  The input increment signal is debounced using an RC circuit and Schmitt trigger. A high-capacity NiMH battery pack and charger from Radio Shack powers the counter.  In empirical tests, the counter ran for an average of 54 hours per charge, indicating that it will need recharging only once each work week.

The cost of parts for each of the five counters was approximately $105.

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