Brief Analysis of the Design Scheme of Infrared Proximity Sensor Si1141
Shiqiang's core infrared proximity and ambient light sensor Si1141 has a high utilization rate in the anti-collision application of sweeping robots due to its low power consumption, small size, low cost and excellent sensing function.
With the advancement of technology and the increasing pursuit of people's living standards, the development of smart homes is changing with each passing day, and sweeping robots are an important member. It is not only an important helper for people's lives, but also a happy experience for users. Because of this, the market size of sweeping robots is increasing rapidly!
In the sweeping work, in order to protect the sweeping robot itself and the furniture from being damaged during cleaning, the sweeping robots on the market have anti-collision functions. At present, the technologies for anti-collision function are as follows: ultrasonic bionic detection technology, infrared distance sensing technology, and anti-collision bar design, each of which has its own advantages. Among them, infrared distance sensing technology, with its small size, low power consumption, low cost, flexible design and rich functions, occupies a very large proportion in the anti-collision application of sweeping robots. In this application, Shiqiang's US Silicon Labs, as the world's supplier of precision mixed-signal devices, has introduced the infrared proximity sensor Si1141, which is widely used for its excellent performance.
Introduction to Si1141:
The Si1141 is a reflection-based, low power infrared proximity and ambient light sensor with an I2C digital interface and programmable threshold interrupt event output. As shown in Figure 1, the sensor includes an analog-to-digital converter, integrated high-sensitivity visible and infrared photodiodes, a digital signal processor, and an integrated infrared LED driver with fifteen selectable drive levels. The Si1141 offers excellent performance over a wide dynamic range and a wide range of light sources, including direct sunlight. The Si1141 can also work under a dark glass cover. Photodiode response and associated digital conversion circuitry provide excellent immunity to artificial light flicker noise and natural light flutter noise.
Advantages of the Si1141 in the sweeping robot collision avoidance application:
 Excellent sensing distance performance: can sense objects in the range of 0~50CM;
The design is simple, flexible and easy to use: as shown in Figure 3, the application circuit is simple and the cost is low. It is easy to operate by connecting through the IIC port.
In addition, the interrupt event output function with programmable threshold also brings a lot of convenience to the design;
Low cost: Si1141 itself is not expensive, and the peripheral circuit is simple, so the cost of the entire solution is
Small size: Si1141 component circuit structure is simple, so the volume is only 2 * 2MM, the launch tube can use a small volume of M3 IR-LED;
Low power consumption: The Si1141 uses pulse-driven technology with an average operating current of only 9uA and a standby current as low as 500nA.
In addition, Si1141 also has ambient light detection function, and the detection ambient light range is wide, 100mlk--128klx; 17-bit resolution, high precision, this function can bring other functional highlights to the sweeping robot!
Si1141 should pay attention to the design of the optical path:
In the anti-collision design of the sweeping robot, the main object is the close-range object. Therefore, in the Si1141 infrared proximity sensing light path, it should be noted that:
1) The infrared light emitted by the infrared LED cannot be directly irradiated onto the Si1141;
2) The infrared light emitted by the infrared LED cannot be reflected on the Si1141 through the "cover";
3) The infrared light emitted by the infrared LED cannot be refracted by the "cover" and then reflected to the Si1141;
Therefore, in order to secure the device, it is recommended to use the optical structure mode of (c) of Figure 4 to effectively avoid such self-contained optical interference. Here, it should be emphasized that the Si1141 has a certain anti-interference ability to ambient light.
Figure 4: Optical structure modeThe other features of the Si1141 and its typical applications are listed below for an in-depth understanding of the chip.
The Si1141 features an integrated infrared proximity detector:
a separate LED driver
15 mA current setting for each LED driver from 6 mA to 416 mA
25.6μs LED driver pulse width
500 mm proximity range, single pulse (2.5 kLx)
150 mm close range, single pulse ("2.5 kLx)
Operates in direct sunlight
Minimum reflection sensitivity "1μW/ cm2
High immunity to EMI in unshielded packages
The Si1141 features on an integrated ambient light sensor:
1 to 128 kLx dynamic range
17-bit resolution
Accurate lux measurements of standard sources can be obtained using IR calibration software
Infrared correction capability
Excellent UV suppression
25.6μs measurement period keeps the total power consumption duty cycle low without affecting performance or noise immunity
Industry's lowest power consumption
1.8 to 3.6 V supply voltage
9.7μA average DC current draw
Assuming a single PS channel, the ALS is visible + ALS IR every 800ms, the average current of the sensor and internal circuitry is 3μA, and the average current of the 6.7μA external LED (assuming 209 mA is 25.6μs per 800ms)
20 nA when power is off
"500 nA standby current
Internal and external wakeup support
Built-in voltage monitor and power-on reset controller
Serial communication
SMBus (I2C compatible) with data rates up to 3.4 Mbps
Slave mode hardware address recognition
Small 10-pin 2x2 mm QFN package
Temperature range: -40 to +85 ° C
Other typical applications of Si1141 by Shiqiang:
Mobile phone
Heart rate monitoring
Pulse oximeter
wearable
Valve control
Smoke Detectors
Non-contact switch
Non-contact slider
Consumer electronics
automated industry
Display backlight control
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