STM32 Journal - Digikey

STM32 Journal
The STM32 L1’s high level of
integration enables it to provide
a single-chip solution, with
the exception of a few analog
signal conditioning circuits,
for many portable medical
applications, including glucose
meters, heart-rate monitors,
and pulse oximeters. For
example, in a glucose meter
(see Figure 4), the STM32
L1 can automatically wake
from sleep when a test strip
is inserted into the device. Its
2-channel DAC can be used to
generate a strip bias, enable
strip calibration, and output
audible instructions and test
results. Timers accurately
control the ADC trigger for
sample measurement, onboard
comparators measure correct
sample staging, and the
temperature sensor logs the
ambient temperature for use in
calculating results. Developers
can also use the integrated
comparators to create a powerefficient
analog watchdog that
monitors an input and wakes
the STM32 L1 when either the
upper or lower threshold is
exceeded (see Figure 5).
A key manner in which the
STM32 architecture conserves
power is through the ability of
the CPU to sleep during ADC
Glucose
Test Strip
Vout
Cal
Reference
Temp
Sensor
Strip Detect
STM32 L1
DMA Controllers
Timers
PWM
1 x 12-bit ADC
26 channels/
1Msps
2 x Comparators
2 x 12-bit DAC
sample capture. To achieve this,
the entire analog data capture
chain needs to be completely
automated, with no need for
CPU intervention at any point
after the chain is initiated.
Specifically, after the CPU
configures and starts the auto
Data EEPROM 4KB
Up to 16KB SRAM
64KB-128KB
Flash Memory
CORTEX TM -M3
CPU 32 MHz
With MPU
8x40
Segment LCD
2 x I 2 C
GPIOs
sample capture, it enters sleep
mode. Between samples, the
ADC enters an automatic shut
down mode until a timer triggers
it. The ADC captures the current
sample, using the DMA to store
the data in SRAM, and then
shuts down again. This process
Power Supply
Reg 1.8V/1.5V/1.2V
POR/PDR/PVD/BOR
RTC/AWU +
80B Backup Regs
USB 2.0 FS
Figure 4 The STM32 L1’s high level of integration enables it to provide a single-chip solution, with the exception of a few
analog signal conditioning circuits, for many portable medical applications such as blood glucose meters.
2 AA battery
Internet
Host PC
LCD Panel
8 x 40
USER Buttons
Voice
repeats until the entire capture
sequence is complete. The
DMA will then wake the CPU to
process the samples that have
been stored in SRAM.
The power savings can be
significant using the unique
ability of the STM32 L1 to
30