Warm Springs Computer Works
Fremont, California

Details of Recent and Memorable Projects
 

TransLink® Fare Payment System, Demonstration Project

The California State Legislature mandated that the public transit agencies in the nine counties surrounding San Francisco Bay adopt a fare payment system that can be used by all agencies. The Metropolitan Transportation Commission sponsored the TransLink smart card fare payment system to meet this mandate.  This project was to adapt the smart card reader to the existing fare gates and operating procedures of the San Francisco Bay Area Rapid Transit District. The overall implementation included several additions to the fare gates; a new intermediary computer, an information display, a discount indicator, a local area network connection, and numerous cables. Part of the installation procedure included an automated procedure to test each connection and function and to direct the installation technician to perform various adjustments and ticketing operations.
 

RF Power Transistor, Linearity at High Power Level

The client manufactures a variety of transistors used for high-power and high-frequency applications.  One particular part being manufactured was being tested on a customer-supplied test system, and, the client's customer recalled the test system on short notice.  The effort on this project was to construct an equivalent test system using components already available.  The client configured the hardware and then called for help in developing the test software.  The test software implemented a two-tone test, where two RF signals (with a narrow frequency separation) are fed to the transistor. A spectrum analyzer is then used to measure power levels at various specific frequencies.  The measured values are then used to calculate an overall linearity factor for the transistor, which is then evaluated to determine the pass or fail condition.
 

Analysis and Reduction of Physiological Data

This project was a software-only effort that read data from a pair of input files, performed an analysis of the data, presented the operator with a running display of the data and data-summary, and wrote two new summary files. The data was used to determine how the pulse propagation time from chest to finger and chest to ear changed when the test subject was put under an emotional stress.

The source of the data was from a human test subject connected to an electrical pulse sensor on the chest, optical pulse sensors on the finger and ear, a respiration activity sensor, and a physical motion sensor. Each of these sensors was sampled 500 times per second and the data recorded in a data file. The subject also had a pushbutton that was sampled once per second. The pushbutton sample and a time signal from a video tape recorder were recorded in a second data file. The duration of each test was up to ten minutes.

The engineering effort in this project was to produce the summary reports showing a second-by-second average of the data and to interpret that data into parameters for heart rate, propagation times, and respiration rate and depth. The challenges for this project were to evaluate the data on a streaming basis at one-second intervals and record key times and amplitudes. These values were then used to produce summary reports for parameters that have periods lasting many seconds.
 

International Space Station, Sequential Shunt Unit

On board the International Space Station, the primary power source will be eight large arrays of photovoltiac cells that convert sunlight to DC current. Each of the large arrays has 82 independent strings of cells that deliver an open-circuit voltage somewhat greater than 200 volts and a short-circuit current of approximately 2.7 amperes. This power is processed and then directed to a battery system. While in sunlight, the solar-array current powers the station directly and charges the batteries. While in darkness, the station is powered only by the batteries.

The Sequential Shunt Unit is the first step in the power conditioning process. The inputs are 82 photovoltiac strings that appear as constant-current sources while the output must appear as a single constant-voltage source. The internal mechanism to make this transformation consists of a field-effect transistor that either short-circuits the current from one string or allows the current to continue on through a summing diode. This elemental circuit is repeated for each of the 82 strings. By controlling the switching of each circuit, only the current necessary to support the desired output voltage is allowed to pass through.

The tests performed on the Sequential Shunt Unit covered three distinct areas, the overall electrical performance, self-protection circuit performance, and the telemetry. The electrical performance involved the output setpoint accuracy and linearity, regulation at various loads, switching frequency, response times for changes in output voltage and currents. The self-protection performance involved imposing stresses or forcing operations that were beyond the normal operating ranges and evaluating the responses. The telemetry tests involved comparing test station measurements to the telemetry data values for the same parameter. All command, control, and telemetry to the Sequential Shunt Unit is by way of a MIL-STD-1553 bus to an internal computer. The internal computer was powered by either an auxiliary control-power connection or by the output.

The test system consisted of a solar array simulator power source, an electronic-load power sink, two power supplies to simulate station battery power, an oscilloscope, a network analyzer, a digital volt meter, relay and switching controls, and a personal computer. All the items listed were controlled with an IEEE-488 bus. The Sequential Shunt Unit was connected to the computer with a MIL-STD-1553 bus. A variety of high-powered switching circuits and analog sensors were present to route measurement points to the instruments. The test software was a combination of Microsoft C code and Hewlett-Packard VEE operating under Microsoft Windows.
 

International Space Station, Rotary Joint Motor Controller

On board the International Space Station, the primary power source will be eight large arrays of photovoltiac cells that convert sunlight to DC current. During normal operation, these arrays are continuously positioned to face the sun while the space station itself rotates so that the same side always faces the earth. The dynamics of orbital mechanics also dictate that every orbit around the earth will require a different positioning profile for the solar arrays. This profile will repeat only once per year. Companions to the solar arrays are the thermal radiators. These must be positioned so that their surface is always shaded from the sun and the earth. In that position, they are able to radiate thermal energy to the blackness of space.

The solar arrays and thermal radiators are positioned by numerous small motors that are driven as either stepping motors or as velocity motors with servo sensors providing feedback. The Rotary Joint Motor Controller drives these motors by converting 120 VDC into DC pulses or levels to drive or hold the motors in stepping mode, or into two-phase variable frequency AC to drive the motors in velocity mode. One noteworthy feature was the absence of an internal processor.

The tests performed on the Rotary Joint Motor Controller covered electrical performance and the command and telemetry channels. The motor-drive capability was tested for voltage, current, frequency, and phase values while driving a resistor and inductor that simulated a motor. The input power was monitored for current draw during the motor drive functions and for the inrush current during the initial power-on sequence. The command and telemetry channels were tested for both command fidelity, data framing, voltage values, and waveform shape.

The test system consisted of power supplies, a counter, an oscilloscope, a digital pattern generator, a digital volt meter, an elaborate switching matrix, a multi-channel chart recorder, and a computer system, all of which were connected with multiple IEEE-488 buses. The test system also had a level-translator to convert the computer and pattern generator's RS-232 outputs to RS-485, simulated motor loads, and several analog adapter circuits in a test fixture. The test software was developed entirely in Hewlett-Packard VEE and ran on a UNIX operating system. A portion of the software was developed on a personal computer under Windows and later moved to the UNIX platform.
 

Airborne Survellance System Components

This project involved combining government-furnished equipment, purchased equipment, and one custom-built adapter into a coherent test system that was used to automate a formerly manual test system.  One noteworthy test involving a PIN diode switch with eight inputs and nine outputs changed from two days of manual testing to about ten minutes of automatic testing. In general, this test system used an artificial intelligence system to select which test to run. Based on the result of that test, either another test was selected, or a report was issued specifying which part to replace. Some of the test programs included on-screen images of selected parts with instructions of where to make test connections.