This is an excerpt from N. Lott, J. Parnell, M. Pickney and M. Sampley, " The Digital Tire Pressure Gauge," ECE 4512: Design I, Department of Electrical and Computer Engineering, Mississippi State University, Fall 2003:

The product we are designing will find a niche in the market for high accuracy, medium cost gauges. Those who purchase our gauge will find themselves better equipped to travel safely, perhaps saving lives in the process.

The first major problem that our group has to address when designing an affordable digital tire pressure gauge is consistency. The inexpensive gauges can be accurate at times, but they are prone to displaying varying values when multiple trial runs are performed. This is a defect that causes the user to lose confidence in the reliability of the product. A reading that is almost accurate can leave the user with no new information and possibly even mislead them. This could bring about a situation where the pressure gauge displayed data that caused an accident with the user. This is a serious liability issue that could end up prompting a recall of the product and/or bankruptcy of a company.

The root of this problem often comes from cheap Analog-to-Digital converters and signal filters that do not properly filter out a single signal for analysis. Most Analog-to-Digital converters are set up to run infinitely, which causes bouncing values in cases where input is not steady. When reading in tire pressure, small amounts of air escapes whenever the nozzle is placed on the tire stem, causing a constantly declining input value. If the Analog-to-Digital converter is allowed to run freely, the output values on the LCD screen will vary over time, confusing the consumer and creating a lack of confidence in what very well may be an accurate converter. We will remedy this problem by introducing a sliding window average to the system software. This allows the Analog-to-Digital converter to take in 10 separate, equally spaced readings over the course of one second. From there, the Analog-to-Digital converter is ignored before sorting the saved values from high to low, discarding the two highest and two lowest readings, then taking the average of the remaining six. This forces the LCD output to be steady and constant.

The other major problem often found in inexpensive tire pressure gauges is a lack of accuracy. This comes from cheap parts that are unable to take precise readings of pressure, or from cheap Analog-to-Digital converters that can only distinguish signal levels at large voltage differences. This problem misrepresents the data, and causes multiple values to be clumped together under a single output reading. Inaccuracy is more dangerous than inconsistency because there is almost no chance that the reading the gauge displays will be dependable enough to base safety decisions upon. This dilemma will be solved with the implementation of an alternate pressure sensor. A more precise pressure sensor will ensure that the digital pressure gauge is accurate within .5 PSI, which will significantly increase the quality of the product.

Another problem is shaping the cover of the digital tire pressure gauge so that it can be gripped easily. Many of the inexpensive gauges have a smooth handle which increases the probability of the user dropping the product. Dropping tire pressure gauges can do serious damage to the sensitivity of the pressure sensor, sometimes knocking it off by 2-3 PSI. A handle with four groves will reduce the risk of damaging the product because the user will be able to firmly grip the tire gauge. The user will be able to place four fingers in the grooves with the thumb free to hold the product.

An additional problem with cheaper models of the digital tire pressure gauge is weather-ability. Often times these gauges have openings in their outer covering that allow liquid to enter into the circuitry of the gauge, which can destroy the product. This is a large dilemma in the products design because the use of a tire pressure gauge is often necessary in undesirable weather conditions.

A rubber sealant outlining the edge of the circuitry will solve this problem. The sealant will be outside of the circuit but directly inside of the opening between the pieces of the outer covering. With this design the water that came through the opening of the covering would not be able to pass through the rubber sealant. This solution will allow the gauge to be used whenever it is needed.