Circuit Note CN-0569 Devices Connected/Referenced ADPD2140 Infrared Light Angle Sensor Circuits from the Lab reference designs are engi- neered and tested for quick and easy system integra- ADPD1080 Photometric Front Ends tion to help solve todays analog, mixed-signal, and ADG3301 Low Voltage 1.15 V to 5.5 V, Single-Channel RF design challenges. For more information and/or Bidirectional Logic Level Translator support, visit www.analog.com/CN0569. LT1761 100 mA, Low Noise, LDO Micropower Regulator LTC4313 2-Wire Bus Buffers with High Noise Margin Infrared Gesture Recognition Module EVALUATION AND DESIGN SUPPORT the background noise and ambient sounds make it difficult for language based touchless user interface systems to accurately Circuit Evaluation Boards capture data. CN0569 Circuit Evaluation Board (EVAL-CN0569-PMDZ) The circuit shown in Figure 1 is a low cost, optical system for ADuCM3029 Ultralow Power, Cortex-M3, Arduino Form Factor common gesture recognition applications. This reference design Compatible Development Board (EVAL-ADICUP3029) transmits pulses of infrared light into space and reads the reflected Design and Integration Files light data received by the light sensor. A gesture object (such as Schematics, Layout Files, Bill of Materials a human hand) which moves into this space reflects infrared light onto the light sensors. The reference design then detects this light CIRCUIT FUNCTIONS AND BENEFITS and generates a response based on the objects position. Touchless user interfaces are a fast-growing technology trend, with The typical gesture sensing range is up to 20 cm and the sample increasing popularity in healthcare, access control, and consumer rate is up to 512 samples per second, allowing the response time based products. This technology enables human-machine interac- and noise rejection to be adjusted to suit the application s specific tion without direct physical contact. These systems utilize gesture requirements. recognition techniques to look for bodily motion such as hand 2 The I C Pmod form factor makes this reference design easy to waving orswipin and interpret those movements as commands. connect up to an external development platform. Algorithms can be This method of interaction relies on data captured by light sensitive developed on a host computer in a high level language, such as devices like cameras or light sensors. Python or MATLAB, then ported to an embedded implementation. Vision and optic-based systems are only dependent on reflected light. This is ideal for public spaces and noisy environments, where Figure 1. CN0569 Simplified Block Diagram Circuits from the Lab circuits from Analog Devices have been designed and built by Analog Devices analog.com Rev. 0 1 of 6 engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page)Circuit Note CN-0569 CIRCUIT DESCRIPTION The ADPD1080 is responsible for pulsing the infrared LED, sensing the ADPD2140 response, converting the analog photocurrents to With gesture recognition, a user interface is able to detect hand digital codes, and sending the data to an external microcontroller movements and patterns and translate them to commands. This 2 via I C. With eight parallel, high performance photodiode input technique requires the system to perform three basic functions: channels and compact design, the ADPD1080 can be used with the ADPD2140 to create a discreet, low cost solution for light angle Detect the beginning and end of a gesture. sensing using synchronized LED pulses. Track hand movement during the gesture. Identify the gesture based on the hand movement. The CN0569 uses two ADPD2140 infrared light sensors connected to the ADPD1080, facilitating both gesture and distance sensing. Figure 3 shows a simplified block diagram of a typical measurement INFRARED LIGHT ANGLE SENSOR channel. The core of the circuit is the ADPD2140 infrared light angle sensor. This device performs 2-axis, single-point measurement of incident angles for infrared light, and multiple devices can be used to triangulate distance. The ADPD2140 has a radiant sensitive area 2 of 0.31 mm , divided into four photodiode channels with a common cathode terminal. When operating at a reverse voltage of 0.2 V, all four channels achieve ultralow typical values for junction capaci- tance and reverse dark current (12.7 pF and 1.74 pA, respectively). Additionally, the ADPD2140 does not require precise alignment because its sensor maintains a linear response within the 35 angular field of view. The ADPD2140 package includes a built-in optical filter with a sharp cutoff of visible light, eliminating the need for external lenses Figure 3. Typical Measurement Channel and preserving the dynamic range of the sensor when placed under sunlight or indoor lighting. When selecting a source of infrared light for this design, it is important to choose a part that operates at a The ADPD1080 has three LED drivers (LEDX1, LEDX2, and wavelength above 800 nm so the light can pass through the internal LEDX3) that can be used to power external LEDs. These LED optical filter of the ADPD2140. The light source should also be drivers operate as current sinks, and the average current drawn by placed at a distance from the sensor such that the reflected light each from the LED supply can be calculated using Equation 1: falls within the 35 field of view. In this reference design, a single L ED PU L SE 850 nm infrared emitter serves as the light source and is placed I = I (1) L ED AV ER AG E L E D PE AK 6 mm away from the first ADPD2140 and 19 mm away from the L ED P ERI OD second, as shown in Figure 2. A 3D printed baffle is placed around where: each ADPD2140 to restrict incident light to within approximately 35, as intense light at steeper angles can contaminate the meas- I is the average current drawn by the LED driver from LED AVERAGE urement. the LED supply in mA. I is the peak current setting of the LED driver in mA. LED PEAK t is the LED pulse width in s. LED PULSE t is the LED pulse period in s. LED PERIOD As shown in Equation 2, the peak current setting of an ADPD1080 LED driver is a product of three factors: the coarse current setting, the fine current setting, and the current scale factor. Figure 2. ADPD2140 + LED Placement on the EVAL-CN0569-PMDZ I = LE Dx L E Dx L ED x Cu r ren t Sc al e (2) L ED PE A K C O ARSE F IN E PHOTOMETRIC FRONT END where: The photometric front end in the CN0569 is the ADPD1080 it is a highly integrated device that includes LED drivers, transimpedance I is the coarse current setting of the LED driver. LED COARSE amplifiers, integrators, analog-to-digital converter (ADC), digital sig- 2 I is the fine current setting of the LED driver. nal processing, and an I C interface. LED FINE LED Current Scale is the current scale factor of the LED driver. analog.com Rev. 0 2 of 6