Digital Physiological Monitoring System (DPMS)
Michael P. ZeleznikIn 1975,
the Psychology Dept. at Indiana University of Pennsylvania hired me to develop a device to monitor the number of licks animals took from water bottles (for research on alcohol abuse). The Physics Dept. allowed me to use their facilities to design and build it.
THE DESIGN: Each water bottle metal tube connected to a CMOS inverter, which could detect microamp current changes. By cascading inverters and employing pre and post R/C filtering, a square pulse was produced when the water tube was licked. This drove a TTL 7400-series BCD counter. This was replicated for 20 parallel channels. The output of these 20 counters was periodically latched into registers, and serially multiplexed to an existing HP digital recorder (vacuum tube vintage). This required a matrix of mini-relays to convert the low voltage TTL signals to the 0-300 volt analog signals needed by the printer. User control (e.g., output intervals, pausing, resetting) was provided through front panel switches, buttons, and LED indicators, and a non-trivial amount of TTL behind it.
THE DEVICE: Comprised three separate physical units.
- 20 channel Digital Event Counter (DEC/2000) shown above
- 20 channel CMOS Touch Switch Bank (TSB/2001)
- 5 channel Digital/Analog Recorder Interface (DARF/502)
These units comprised the following components, built on hand-etched double-sided printed circuit boards:
- 144 TTL ICs (7400s)
- 10 CMOS ICs
- 56 mini relays
- misc R/C components
- switches, buttons, LEDs
- power supply, cooling fan
- custom aluminum brackets / cases
- and hundreds of feet of wiring.
|All pictures were taken by Chuck Semmell|