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49 Engineering a More Sustainable Future | ADI Analog Devices has designed the industry's first 10BASE-T1L MAC- PHY ( ADIN1110 ) , which is a single pair Ethernet transceiver with embedded MAC. The ADIN1110 communicates with an embedded microcontroller using a simple SPI bus, which reduces both power consumption and firmware development time for the sensor. In this article you will learn how to design a tiny but powerful sensor, as shown in Figure 1. This article will cover: X How to design a small, shared data and power communications interface X How to design an ultralow noise power supply for the sensor X Microcontroller and software architecture choices X Choosing a suitable MEMS vibration sensor X Integrating a digital hardware design and a mechanical enclosure X Examples for data collection UI at your PC How to Design a Small, Shared Data and Power Communications Interface What Is PoDL? Power and data are distributed on a single twisted pair using an inductor capacitor network, as shown in Figure 2. High frequency data is coupled to the data lines through series capacitors, which also protect the ADIN1100 10BASE- T1L PHY from DC bus voltages, as shown in Figure 2 ( a ) . Figure 2 shows a power supply connected at the PSE ( power sourcing equipment ) controller via a coupled inductor connected to a data line. The 24 V DC power biases the AC data bus as illustrated in Figure 2 ( b ) . In Figure 2 ( c ) , the current path is shown as I PWR between the PSE and PD ( powered device ) , with the power extracted from the line using a coupled inductor at the CbM sensor node. To protect against incorrect polarity cable installations—for example, a fault where the 24 V DC of the PSE PHY is wired to the 0 V DC of the PD PHY—a bridge rectifier diode is recommended. For EMC robustness, a TVS diode with working voltage greater than 24 V DC is required. Additional EMC components can be used ( for example, high voltage capacitors on signal wires ) if the sensor hardware design is larger. Designing a small PoDL circuit using all these components can be challenging, but fortunately most vendors have competitively sized solutions for rectifier diodes, TVS diodes, and passive components. Generally, components with ultralow capacitance must be chosen to minimize signal distortion. The coupled inductor and capacitor values are recommended to have inductance and capacitance values of 220 µH and 220 nF respectively but can be larger in simulation or testing for design margin. A selection of very small size components that can be used for sensor design are listed in Table 1. Table 1. Component Selection for PoDL Interface for Small Sensor Designs How Do I Design a Small PoDL Circuit? Figure 2 includes the coupled inductor and series capacitors as the most basic components required for the PoDL operation. Additional components are required for robustness and fault tolerance. Because the PoDL coupled inductors are nonideal components, some differential to common-mode conversion will occur. This common-mode noise will degrade signal quality. Connecting a common-mode choke close to the cable connector helps to mitigate against this nonideal behavior and protects the design against common-mode noise coming from the cable. The common- mode choke ampacity and DCR will need to be examined to ensure that they can support adequate power delivery for the sensor. Component Part Number Comment Common-Mode Choke Würth 744242471 470 µHs TVS Bourns CDSOD323-T36SC Coupled Inductor (power) Coilcraft LPD5030-224MRB 220 µH Bridge Rectifier Diode Bourns CD-HD2006L Series Capacitance Taiyo Yuden HMK107C7224KAHTE 220 nF 1 Figure 1. 10BASE-T1L single-pair Ethernet conditioning monitoring ( vibration ) sensor prototype. Adobe Stock / Yingyaipumi – stock.adobe.com