The heart and brains of the hardware system, this beast was all hand designed, hand wired, and hand built. It features eleven separate ten bit analog input channels, two binary input channels, one status output, and central power regulators for all external devices. The whole system is powered by +13v and -5v, and draws about 1 amp/hour when all devices are in use. Each device is plugged in with 1/8" stereo jacks, that supply the needed three connections for each channel (ground, Vcc, and data). Five separate 9 volt 100mA regulators, and one -5 volt 500mA regulator supply each channel's Vcc line with the appropriate voltage and current for the device plugged in. This means that the entire system, and all it's devices, are powered by one power supply, which makes life much easier, and keeps battery costs down.
The component level chip used for the analog to digital converter was the TLC1542. This chip features eleven separate analog inputs, and its own internal system clock. The output is a digital ten bit signal (1024 steps of resolution), between Vref- and Vref+, which are ground and +5v, respectively. So, the voltage input from each channel can be calculated, with resolution to 4.88 millivolts. That reading can then be sent to other device specific conversion methods, that will calculate the appropriate unit of measurement for that channel.
The A/D box communicates with the computer via the parallel port, which provides 8 usable write bits, and 5 usable read bits. Two read bits are used for the TLC1542's needed data and EOC lines, two of the other read bits are used for two separate binary inputs (for motion detectors), and the remaining bit is used as a box status, so the software can verify when the unit is plugged into the computer. Three of the write bits are used for the TLC1542's needed address, CS, and I/O system clock lines, while the other two are used as a power indicator, and the status box output. The other three write bits are left open, and could be used to trigger remote equipment (video/still cameras, audio recorders, etc.). The status box is merely a luxury, as it will trigger a small audible alarm and flashing LED when a substantial anomaly occurs.