Motor Driver/Motor Watchdog Circuit

Motor drive circuitry is composed of a series of power FET transistors, passive components, and two voltage comparators. Built into the motor drive circuitry is an RC timer which times how long the motor runs each time it is turned on. If the motor runs for more than an average of 4 seconds, the circuit will time out and disable the motor. A unique feature of this circuit is that control lines to and from the microprocessor circuit allow the microprocessor to perform a complete functional test of the motor drive circuit without running the motor. The microprocessor performs this test function every several minutes to assure its continued functionality. An input from the watchdog circuit prevents motor operation if the watch- dog timer expires.

Cassette ‘Type’ Sensor Circuit

The cassette ‘Type’ sensor system consists of three pins protruding from the button of the pump mechanism that interface to the attached administration set and associated circuitry. Each type of administration set designed to work with the CADD-Prizm®pump contains a unique ‘code’ programmed into the set via nubs molded into the plastic. When a set is latched to the pump, the nubs press against the pins in the pump mechanism in a pattern unique to that set type. Optical detectors and electronic circuitry on the circuit board encode this pattern and report the information to the microprocessor. This feature allows automatic rate selection dependent on the type of set attached. This system also acts as a safety feature to detect a damaged or detached set. If, during operation, the microprocessor detects all pins extended, the pump will enable audible and visual alarms and stop delivery. Redundancy in the pattern prevents single fault failures from causing over or under delivery of fluid. Additional circuitry allows these sensors to be turned on and off by the microprocessor to conserve battery power. Additionally, control of sensor power allows the microprocessor to test the sensor inputs in both the powered and unpowered states, thus allowing detection of sensor fault conditions. Care should be taken not to damage these sensor pins.

Latch/Lock Sensor Circuit

Latch and Lock sensors allow the microprocessor to detect the positions of the latch and lock buttons. This prevents attempted fluid delivery when the set is not correctly latched to the pump. In addition, it allows the microprocessor to stop fluid delivery and enable audible and visual alarms if the set is unlatched during fluid delivery. Opposing infrared transmitters and receivers on both the latch and lock buttons allow the microprocessor to detect their open and closed positions. Additional circuitry allows these sensors to be turned on and off by the microprocessor to conserve battery power. Additionally, control of sensor power allows the microprocessor to test the sensor inputs in both the powered and unpowered states, thus allowing detection of sensor fault conditions.

Voltage Detector Circuit

Low voltage detection is performed by part of the watchdog circuit and by the microprocessor via software. Three low voltage levels are detected. The first two levels are detected by software and the third by hardware. The first level to be reached is the Low Battery Warning threshold which occurs when the battery voltage decays to a nominal value of 6.8 volts. An Analog to Digital Converter (ADC) built into the microprocessor allows the micropro- cessor, via software, to monitor the battery voltage. At the Low Battery Warning thresh- old, the microprocessor enables a periodic series of beeps and displays a low battery warning message on the LCD. As the battery voltage reaches a nominal value of 6.3 volts, the software disables delivery, places a battery depleted message on the LCD, and enables a constant two-tone audible alarm. When the battery voltage decays to a nominal value of

5.6volts, a hardware reset circuit is triggered which places the microprocessor in reset. This prevents ambiguous microprocessor operation when the battery voltage continues to decay.

The hardware reset continues until the battery is completely discharged or until it is removed. Once the pump controller goes into low battery shutdown, only replacing the old battery with a fresh one will clear the condition.

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