|
Squires Engineering
was contracted to design and build a custom test system for performing
functional testing of their Laars LX Heater Controller circuit boards.
The LX board is a small microprocessor based design which includes
a backlit LCD panel, an RS-485 interface, a 10-bit A-to-D converter,
membrane switches, and various sensor inputs for 24 VAC signals.
The design also utilizes an EEPROM for storing configuration settings.
|
client:
Waterpik Technologies Inc. 1758 Corporate Circle Petaluma, CA 94952 |
 |
|
|
The complexity of the LX controller made it impossible to test the board adequately via direct connections to the PCB. Squires Engineering proposed modifying the embedded firmware to support functional testing during product manufacturing. The client provided source code to Squires Engineering for that purpose. Squires Engineering designed a set of RS-485 messages to place the board into a test mode and added new code to perform specific diagnostic operations based upon commands received over the RS-485 link:
The challenges in doing this were to integrate these new diagnostic functions without exceeding the available EPROM space available, and without disturbing the functionality of the normal operational firmware. A Windows-based test program running on a PC was to be used to provide the test control logic, however some specialized hardware was required to communicate with the LX PCB over RS-485, and to provide simulated input signals for the LX board under test. A custom embedded controller PCB was designed by Squires Engineering for this purpose. This PCB was called the LX Test Set Controller. The LX Test Set Controller was designed to be the interface between a PC serial port and a custom test fixture for probing a Laars LX PCB for testing. The idea was that simple ASCII commands and responses would be used on the EIA-232 serial port to control the LX Test Set Controller to carry out tests on the LX PCB in the test fixture. This ASCII command set was used by the Windows test program for performing all testing operations. As an added benefit, a serial terminal could be used interactively during development of the LX Test Set Controller to debug its hardware and firmware. This allowed concurrent development of the Windows test software and the LX Test Set Controller, thereby minimizing the overall development schedule. The LX Test Set Controller was implemented as a two-sided PCB and mounted in a NEMA enclosure along with the necessary power sources. The controller connected to a custom test fixture via ribbon cables. The design and fabrication of the custom test fixture were subcontracted to a firm specializing in test fixtures. Two LX Test Set Controller chassis were hand built by Squires Engineering and delivered to STI in Melbourne, Florida, where LX PCBs are to be built and tested. The test system is operated using a Windows based test program also developed by Squires Engineering. The Windows program uses a dual-pane design that shows test summaries on the left side of the screen, and shows detailed test information on the right side of the screen.
DEVELOPMENT SCHEDULE The entire LX PCB Test System development was performed in about six weeks. This development included the following activities:
|
|
