Dialog Semiconductor DA14681, Руководство по оборудованию

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UM-B-077
DA14681 Wearable Development Kit Hardware Manual
User Manual Revision 1.2 06-Apr-2017
CFR0012 27 of 47
© 2017 Dialog Semiconductor
4.9 Heart Rate Monitor (HRM)
Traditional heart rate measurement equipment has been restricted to the use of chest straps linked
to an external device, such as a smartphone via the BLE protocol. These HRM solutions exhibit
some disadvantages: chest straps are often inconvenient and uncomfortable to wear, while
smartphones can be difficult to be monitored when exercising.
Wrist-based HRM technology introduces a new way of biometric monitoring by providing a more
convenient and comfortable way to measure heart rate, rivalling the accuracy of chest-strap-based
designs.
The DA14681 wearable reference design incorporates such a wrist-based heart rate monitor based
on the
DI5115 HRM module from Dyna Image. The DI5115 sends bright light via Green LEDs (D10B,
D11B) through the skin and then measure the amount of light that comes back. Blood absorbs light,
so variations in light that the heart rate sensors detect can be used to determine your pulse rate.
The DI5115 module uses a set of combined IR-Green LEDs (IRG1615D01, 940 nm 530 nm Green
Infrared LED from Dyna Image) that comes in single package. The key characteristics of the LEDs
can be found in
Table 13 , Table 14 and Table 15 .
Other green LEDs (such as QBLP676-IG from QT Brightek) can be used to replace the IRG1615D01
LED module. The only requirement is that they must have the same wavelength and the cross point
must be checked against the new package.
In this implementation the IR LED is not used. For maximum power transfer it is advised that the
value of the resistors R180, R181 and R190 should be 0

.
For optimum performance the pitch between the LEDs and HRM module (DI5115) should be 3.5 mm.
Table 13: Green - IR LED Maximum Ratings
Parameter Symbol Rating Green Unit
Power
Dissipation at or below 25°C
P
D
100 72 mW
Continuous Forward Current I
F
20 20 mA
Peak Forward Current I
FP
100 100 mA
Reverse Voltage V
R
5 V
Operating Temperature T
OPR
-40 to +85
°C
Storage Temperature T
STG
-40 to +85
°C
Soldering Temperature T
SOL
≤ 260 °C
Table 14: Electrical Characteristics
– IR LED
Parameter Symbol Min Typ Max Unit
Radiant Intensity l
E
0.92 1.83 - mW/sr
Forward Voltage V
F
-- 1.25 1.7 V
Reverse Current I
R
-- -- 100
μA
Peak Wavelength
λ
P
-- 940 -- nm
Spectral Line Half-width
Δλ
-- 50 -- nm
Rise/Fall Time T
R
-- 50 --
ns
T
F
-- 20 --
Viewing Angle
2θ1/2
-- 120 -- deg