MANUFACTURING STEPS OF THE SECOND GENERATION PROTOTYPE
MANUFACTURING STEPS OF THE SECOND GENERATION PROTOTYPE
Construction Details – Second Generation Prototype
To simplify the design, the miniature connector between the main board and the sensor board was removed. The interconnecting wires are directly soldered to both boards and the hole is sealed by silicone rubber. To cut cost, the main PCB is held in position by glue rather than a screw and a battery with pins was used in place of the battery holder. The mechanical construction of the improved design is shown under.
Mechanical Construction (Top and Bottom View)
The photographs of the actual PCB are shown under.
Prototype PCB of the Improved Design (Top and Bottom View)
The photographs of the assembled gauge are shown under.
Assembled Tire Pressure Gauge with and Without the Front Plexiglass
Bill of Materials – Second Generation Prototype
| Item | Quantity | Reference | Part |
| 1 | 1 | BT1 | CR2032, 3 V Lithium |
| 2 | 2 | C4, C5 | 100n |
| 3 | 1 | D1 | LCD, 23 x 1 Segments |
| 4 | 1 | J1 | Connecting Wires and MPXY8020 |
| 5 | 3 | J2, J3, J4 | Headers for Debugging |
| 6 | 1 | SW1 | Push Button |
| 7 | 1 | U1 | MC68HC908GT8 |
Schematics – Second Generation Prototype
The initial prototype used an LCD display targeted for a low–cost digital watch. Testing of the prototype revealed that the larger display should be used for improved readability. Since the design was not meant for mass production, ordering a custom made LCD display was not adequate and the design had to use an industry standard LCD display. The display which was chosen does not use the multiplexed driving scheme and therefore requires a higher number of I/O pins. To match this requirement, the MC68HC908GP32 microcontroller was chosen and later exchanged for pin compatible MC68HC908GT8 which features an internal clock generator unit and does not require an external crystal. The schematic diagram of the redesigned application can be seen under figure.