TI Design and Software Examples
3.1.7.2
Test Data
shows current measurements both with and without the BOOST-IR module connected to the
board. This is to show the contribution of just the MSP430 versus the consumption of the whole system.
Table 7. Current Consumption
Idle Current With BOOST-IR
Idle Current
Software
(No Buttons Pressed)
(MSP-EXP430FR4133 Only)
IR Emitter
830 µA
4.0 µA
IR Receiver
1059 µA
238 µA
Current consumption when the BOOST-IR module is present is much higher due to the consumption of
the IR demodulator TSOP58238 module. The TSOP58238 module on its own consumes approximately
800 µA, so it makes up the bulk of the current consumption of the system. For product designs where IR
RX function is not needed, only TX, this device could be eliminated and a lower current consumption in
idle mode more like the MSP-EXP430FR4133 current for IR Emitter shown above could be achieved.
Note that while sending a transmission by pressing a button, the current peaks – this peak current
depends on the R value that you have selected for R2 (which also affects range as detailed below).
The current consumption for IR Receiver mode of just the MSP-EXP430FR4133 was measured at
approximately 238 µA. This is higher than the IR Emitter code, because while the IR Emitter code can
remain in LPM3 until a button is pressed, the IR Receiver must have the timer capture set up with the
timer module sourced from the high-frequency SMCLK to have a high enough timer resolution to decode
the signals. To keep SMCLK enabled while idle, IR Emitter code can only enter LPM0, because this is the
lowest power mode in which SMCLK is on. See the MSP430FR4133 data sheet (
) for more
details about low-power modes (LPMs) and current consumption.
Table 8. Range Testing
Resistor Used for R2 (
Ω
)
Range (meters)
47
8 m
4.7
20 m
By default, the BOOST-IR module comes with a 47-
Ω
resistor for R2. R2 controls the TX current for the IR
LED. This has a direct effect on the brightness of the IR LED and therefore the range of transmission that
is possible. When testing with the TX and RX code examples, the maximum range for transmitting from
one BOOST-IR to the other was 8 meters with the default 47-
Ω
R2 – at longer distances, transmission and
reception became unreliable. When the value of R2 was changed to 4.7
Ω
, the LED is driven with more
current and able to transmit much farther. In our test, we achieved a 20-meter transmission distance with
this resistor. Using a smaller R2 allows for longer transmission distances at the expense of increased
current consumption. For transmission power this high, external power must be provided, because the
MSP-EXP430FR4133 and other LaunchPads are unable to provide this much power directly. In a
production design, experimentation should be used to help determine the best resistor value to achieve
the desired transmission range while still fitting within the design’s power budget.
3.1.8
Design Files
For software files, see the
MSP-EXP430FR4133 Software Examples
For hardware files, see:
•
BOOST-IR Hardware Design Files
and
and
.
•
MSP-EXP430FR4133 Hardware Design Files
21
SLAU598A – December 2014 – Revised July 2015
BOOST-IR Infrared (IR) BoosterPack™ Plug-in Module
Copyright © 2014–2015, Texas Instruments Incorporated
