SIM225 Technical Reference Manual
40
© Serious Integrated, Inc.
SIM225_TRM_A1ENUS
Revision A1
SPEAKER/AMPLIFIER
The SIM225 includes an on-module high quality
PUI 1308MS-R speaker
driven by a small but efficient
Analog Devices SSM2301 750mW Class D Audio Amplifier
. Driven by the RX MCU’s on-chip Digital to
Analog converter (
RX_AUDIO_OUT: DA0/P03/C2
) and enabled via the
RX_AUDIO_EN#
signal (RX Port
P02/B1
), the speaker can drive reasonable quality and volume audio output for user prompting and
feedback under software control. An appropriate cabinet/case design around the SIM225 is important in
forming an audio cavity to improve volume and bass response.
When solely powered by
USB Device Power (+5_USBF)
there is insufficient power to drive the
audio speaker/amplifier subsystem: turning on this subsystem without sufficient power will
typically cause a reset as the USB host (PC or hub) voltage drops due to excessive load.
TEMPERATURE SENSING
MCU ON-CHIP TEMPERATURE SENSOR
The SIM225’s MCU contains an on-chip temperature sensor, readable by the on-chip 12 bit ADC with a
typical accuracy of +/- 1%. This sensor may be suitable for keeping track of general system temperature,
but is not an accurate ambient air temperature sensor. Air temperature sensors generally require
separation from the circuit board to isolate them from heating sources on the PCB, especially the LCD
backlight. As a result, the RX MCU’s temperature sensor will often read a few degrees above that of the
ambient temperature. In addition, software-managed calibration may be required before use.
See the
RX63N/RX631
datasheet for more hardware specifications and programming information.
PCB TEMPERATURE SENSOR
Some SIM225 variants also contain an
On Semiconductor NCT75
for measuring the system (board)
temperature. This sensor is excellent for keeping track of general system temperature, but is not an
ambient air temperature sensor: accurate air temperature sensors require separation from the circuit
board in order to isolate the sensor from heating sources on the board. As a result, the NCT75 will
typically read a few degrees above that of the ambient temperature.
The high level specifications for this device are:
Parameter
Value
Accuracy
Typical @ 25°C
±0.5°C
Worst Case @ 0°C to +70°C
±1.0°C
Supply Current
Typical
440uA
Max
800uA
Shutdown Typical
3uA
The sensor supports 12 bit resolution readings in approximately 50ms.
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