Page 444 - Handbook of Biomechatronics

438 Graham Brooker

size. For precision voltages required by the various electronic components in
the device, low dropout (LDO) linear regulators are typically used as they
provide excellent efficiency and small size if the minimum headroom is
maintained.
Insulin pump manufacturers have made good progress in reducing power
consumption to maximize battery life, with modern pumps able to operate
between 3 and 10weeks before battery replacement is required. Many
pumps on the market use single AA or AAA alkaline or lithium batteries.
Primary cells are common, but rechargeable cells can be used for the
long-term cost savings. However, because of their lower capacity, the latter
need to be recharged more often.
Because of the variety of batteries that can be used in pumps, they typ-
ically rely on simple battery-voltage and, sometimes, temperature measure-
ment. These readings of voltage and temperature are digitized and processed
by the microcontroller to determine the remaining capacity of the cell. This
is indicated by the number of charge bars on the LCD display in the usual
manner, with an audible warning when the battery needs to be replaced
(Mossman, 2010; Ganesan, 2013).

4.2.4 External Interface
Simple external interfaces consisting of a custom alphanumeric mono-
chrome LCD display and a few push button switches allow the user to tailor
basal and bolus dosages to their requirements. The display typically includes
information about insulin dose and rate, battery capacity as well as date and
time and various alarms (Mossman, 2010).

4.2.5 Self-Test and Alarms
All insulin pumps must perform a self-test on switch on to meet FDA
requirements. This includes tests of all critical processors, critical circuitry,
indicators, and displays. Some models even incorporate a separate processor
to monitor the main processor for anomalous operation. The most common
form of self-test is a separate watchdog timer that monitors the time taken by
the processor to execute various functions and flags an error if this is outside
normal limits.
Power supplies are monitored for undervoltage and overvoltage condi-
tions and motor loading is monitored with motor-stall detection being a pri-
ority as it is a critical failure.
Insulin pumps require audible and visible alarms. These use an audio
beeper and the LCD display as well as separate LEDs. Typical systems use
a flashing green LED during normal operation and a red LED and an audio