SUPERIOR MOTION SENSOR Using Microwave Doppler Radar

An earlier design introduced a touch solid-state AC switch. The new version advances this concept with a sophisticated human radar sensing system that can also be configured for IoT and smart automation. The system uses 70 per cent Indian components and is entirely Indian-engineered. At its core lies a microwave doppler radar sensor that detects human motion with far greater reliability than traditional PIR or IR-based systems. Unlike PIR sensors that depend on heat signatures and often malfunction under sunlight, near heaters, or behind curtains, the microwave radar delivers superior penetration through nonmetallic barriers, immunity to heat-induced false triggers, reduced sensitivity to small animals, and omnidirectional detection without requiring a direct line of sight.

- ASHWINI KUMAR SINHA

Where most motion switches rely on PIR sensors and frequently cause false triggers, this radar-based system eliminates such issues. It also integrates an LDR to function only under low-light or nighttime conditions, making it ideal for automated lighting systems.

The components for the system have been selected such that Indian substitutes are available wherever possible, enabling over 70 per cent localisation in the design. Table 1 lists the Bill of Materials, including part names, numbers, manufacturers, and Indian substitute options where applicable.

Design

In this upgraded version, the separate optocoupler and triac ICs have been replaced with a single integrated optotriac that combines both functions. This component, sourced from an Indian manufacturer, can directly drive AC loads up to 1A RMS across the 110-230V range, as specified in the VO2223A datasheet.

This capability enables automatic control of standard LED and CFL bulbs used in residential and commercial environments. An FPC connector allows interfacing with development boards, including the IndusBoard Coin, extending functionality for IoT-based human radar sensing or solid-state relay applications.

This single compact design supports multiple modes of operation, allowing configuration for standalone use or full IoT integration.

The RCWL microwave Doppler radar detects human presence using the Doppler effect. An optional LDR input allows night-only operation, keeping lights off during the day and automatically activating them at night when motion is detected.

According to the optotriac datasheet (refer Fig. 2), the triac can directly drive an AC bulb via pins 8 and 6. A snubber circuit may be added for inductive loads. Fig. 2 presents the VO2223A configuration circuit.

The design includes an FPC connector for IoT board integration and can be configured in four modes: Mode 1, Mode 2, Mode 3, and Mode 4.