Electronics hobbyists, experimenters and constructors of microcontroller project frequently need to measure/detect voltage, current, frequency, temperature and… proximity. Most measure ments/detections can be carried out using pre-wired add-on modules integrated with suitable sensors/transducers. Unfortunately, real-motion detection requires rather more sophisticated and thus more expensive sensor. However, the microwave motion sensor module -HB100- introduced here makes the task sweet and simple. HB100 miniature microwave motion sensor is an X-band, Bi-static doppler transceiver module. This module is ideal for alarm, motion detection, vehicle speed measurement, automatic lighting, and door projects.
HB100 – General Features
The Doppler Effect
Doppler radar uses the same principles discovered by Christian Doppler when observing sound and applies them to electromagnetic waves. Using the Doppler Effect is a great way to measure relative speed. In practice, the Doppler Effect is a shift in frequency perceived by a receiver from a signal source due to relative movement of the sender and/or receiver. In a Doppler radar system, a known frequency signal is transmitted from an antenna which is pointed at a reference object. A separate antenna is used to receive the signal that is reflected back from the reference to measure the Doppler shift of the signal. A simple Doppler module, also called as the microwave motion sensor, can be easily integrated into multiple types of systems for various purposes. Doppler modules have an internal oscillator used to produce the signal frequency transmitted as the source. The received signal is then mixed with this set signal, which produces an output that is a sinusoid containing the frequency difference between the sender and receiver signals. Usually, these values need to be processed in a tangible way and is usually done with the help of a microcontroller.
HB100 – Insights
The HB100 module consists of Dielectric Resonator Oscillator (DRO), microwave mixer and patch antenna. The module operates at +5 Vdc for Continious wave (CW) operation, but module can be powered by +5V low duty cycle pulsed trains in order to reduce its power consumption (sample & hold circuit at the IF output is required for pulse operation). The following indicators should be considered when using the HB100 module.
The easiest way for a microcontroller to read data from an analog device is if it outputs a dc level voltage. Although some modules have this feature built into them, many others output just an AC signal, so a frequency-to voltage (F-V) circuit must be implemented. This F-V circuit can be used to calibrate the output data for a specific set of expected frequencies coming from the module to contain it in reference voltage range. Sampling of the available data and the manipulation of it through software is needed to make it useful for the system. This pre-processed value can then be manipulated using Doppler equations to find the speed of the target object.
Arduino + HB100 – Unlimited!
If you are in a plan to build something similar like an intelligent device on a door which alerts you about an attack in progress on the other side of the door, then go through this amazing Arduio + HB100 project:“Microwave Motion Sensors for Fun and Profit” (http://jpnelson. com/post/ 37623468093/microwave-motion-sensors-for-fun-and-profit-hb100). Author’s lab (TechNode PROTOLABZ) is waiting for the arrival of more HB100 modules from eBay, and you can expect another unsual Doppler Radar project from the author in near future!