X-Band Motion Detector
The X-Band Motion Detector's sensor is a common component in security systems and automatic door openers and can detect movements within a room, yard, or even on the other side of a wall.
The X-Band Motion Detector operates in the X-band frequency, at 10.525 GHz and indicates detected movements with oscillations in its high/low output.Sensitivity is manually adjustable with a potentiometer, offering direct line of sight detection from roughly 8 to slightly over 30 ft (~2.4 to 9+ m)
- Operation frequency of 10.525 GHz
- Able to detect motion through walls and windows
- More immune to false triggers than passive infrared motion sensors
- Active-high enable pin with internal pull-up resisto
- Trim potentiometer on the back for manually adjustable sensitivity
- 4-Pin SIP header for breadboard or through-hole prototyping
- Built-in series resistor for compatibility with the Propeller microcontroller and other 3.3 V devices
- Plated test point hole for monitoring pre-comparator signal
- Power supply requirements: regulated 5 VDC, 8 mA
- Communication: High (3.9 V) / low (0 V) signal oscillates with motion
- Dimensions: 1.8 x 1.75 x 0.75 in (46 x 45 x 19 mm)
- Operating temp range: +32 to +131 °F (0 to +55 °C)
- Security systems
- Automatic door openers
- Automatic lighting
- Nuisance animal deterrence
Motion in the detection area causes oscillations at the module’s OUT pin, which can be detected by a microcontroller. The front of the device is the antenna PCB, a printed circuit board surface with the module’s transmit and receive antennas, as shown in Figure 1. The device should be oriented so that this surface faces the detection area. When the enable (EN) pin is held high or left floating, the device takes brief, periodic, low power Doppler radar measurements. The frequency of the high/low signals the output (OUT) pin transmits corresponds to the speed of the motion.
Figure 2 shows a test circuit for either the BASIC Stamp 2 or Propeller microcontrollers. The optional enable (EN) pin is connected to I/O pin P9, and the module’s output signal (OUT) pin is connected to P8. The EN pin can be held low to disable the device. When the EN pin is pulled high it enables the device. Likewise, if the EN pin is left floating, an internal pull-up resistor keeps the device enabled whenever it has power. The OUT pin oscillates whenever motion is detected, and in general, the more motion, the faster the oscillations.
This test procedure provides a quick-start for the BASIC Stamp 2 or Propeller microcontroller.
- Build the circuit shown in Figure 2.
- For close range motion measurements while connected to a computer, turn the potentiometer adjustment all the way counterclockwise
- Connect power and programming cable to your microcontroller board.
Resources and downloads
BASIC Stamp 2 microcontroller
- Test X Band Motion Detector.bs2 is featured in this document’s Test Code section and is also available for download in the following link
- Download and open Test X Band Motion Detector.bs2
- Use the BASIC Stamp Editor and load it into the BASIC Stamp microcontroller
- Test X Band Motion Detector.spin is featured in this document’s Test Code section and is also available for download from the following link
- Open the Parallax Serial Terminal and make sure it is set to the Propeller Chip’s programming port at a baud rate of 115200 bps.
- Use the Propeller Tool software to load the application into the Propeller chip.
- As soon as the Propeller Communication window reports “Loading…” click the Parallax Serial Terminal’s Enable button.
Monitoring the Sensor Output
Figure 3 shows terminal messages from the BASIC Stamp and Propeller microcontrollers as each one monitors an X-Band Motion Detector.
- Make sure nothing within a 10 ft (3 m approx) radius is moving as you monitor the Debug Terminal. The Debug Terminal should display values of zero or close to zero along with a“Motion not detected.” message.
- Move your hand toward or away from the face of the antenna PCB, and verify that the Debug Terminal displays larger numbers along with the “Motion detected!” message.
Calibration and Sensitivity
The X-Band Motion Detector’s detection range can be adjusted by turning the Sensitivity potentiometer on the back of the device. The “motion/no motion” threshold constant ‘MoveThreshld’ in each example program can also be adjusted, which allows it to ignore small or brief, quick motions. Larger MoveThreshld values require more motion (larger values in the ‘cycles’ variable) to trigger a detection; smaller values require less motion to trigger a detection. The device’s sensitivity may vary with different kinds of walls and window blinds. For example, direct line-of-sight detection can be adjusted from approximately 8 to slightly over 30 ft (~2.4 to 9+ m). The sensor will still be effective through walls and windows, but not through conductive metals, and testing for the conditions under which it will be used is recommended.
The device’s sensitivity also varies with the object’s angle, which in turn varies with the antenna radiation plots in Figure 4. It is most sensitive to objects directly in front of the antenna PCB (Figure 1) which corresponds to an angle of 0° in Figure 4. Sensitivity is maximized in the areas where the plot is between the two outermost circles. This is the region between 0 dB (full power signal) and -3 dB (half power signal).
For example, on the horizontal plane, the antenna’s radiation pattern stays above half power from approximately 300 degrees to just over 45 degrees. In the vertical plane, the half-power beam width ranges from about 340 to 20 degrees. Keep in mind that angles corresponding to larger –dB values (closer to the center of a graph) indicate that the object will have to be closer to the device for it to detect motion. So, the sensor will still detect motion at angles outside these half-power beam widths, just at a closer range.
Theory of Operation
The X-Band Motion Sensor is constructed of two boards connected by posts: a control board, and the antenna PCB with the Doppler sensor. Block diagrams of these boards are shown in Figure 5. When the enable pin is either held high or left floating, the control board cycles the Doppler sensor’s power at 2 kHz, 4% duty cycle. The Doppler sensor’s 10.525 GHz oscillator signal is routed to the Tx antenna, and also to a mixer diode. The mixer diode’s IF output contains signals with the sum and difference of the transmitted and received frequencies along with components of the original signal and some harmonics. The difference signal’s frequency that results from mixing the outgoing and returning signal frequencies is the important component. It oscillates at a frequency corresponding to how much the returning signal has been either compressed or stretched as a result of the Doppler Effect that an object has on the signal as the object moves toward or away from the sensor.
The Doppler sensor’s IF terminal passes the signal to the control board, where a low pass filter removes all the higher frequency signals and leaves behind the difference signal. This signal passes through an amplifier whose gain can be adjusted by the control board’s potentiometer, and can be monitored by probing the test point, which is a plated hole labeled TP. The TP signal passes though a comparator, which transforms the signal with the difference frequency to a high/low digital output. The difference signal’s frequency is related to the component of the object’s speed toward or away from the sensor by this equation:
In contrast to speed guns, which use a wave guide to direct the antenna radiation pattern, the X-Band Motion Detector’s antenna has a wide radiation pattern to convert velocities from multiple points to oscillations that notify the microcontroller that movement was detected. This device is designed to detect motion, not to determine speed of a moving object. However, an application may still use a rearranged version of the Fd equation to determine speed provided everything else in the detection area stays still.
Pin Definitions and Ratings
|1||EN||High to enable the Doppler sensor, low to disable. Accepts 3.3 V or 5 V high signals.|
|2||OUT||Output signal that oscillates high/low = 3.9 V/0 V to indicate detected motion. This output pin has a 1 kΩ series resistor to keep it compatible for direct connection with the Propeller microcontroller’s 3.3 V I/O pins.|
|3||+5V||+5 V power supply|
|4||GND||0 V = ground|
Resources and downloads
FCC Notice and Liability Disclaimer
These modules (boards) are not FCC approved. They are designed to comply with FCC Part 15 Rules and Regulations. They are not in a finished product form. They are strictly intended for experimental purposes only. If you wish to use these modules in an actual product (a non-experimental capacity), the module must first be designed into the product then the whole product must be approved by the FCC. SimplyTronics is not responsible for special, incidental, or consequential damages resulting from any breach of warranty, or under any legal theory, including lost profits, downtime, goodwill, damage to or replacement of equipment or property, and any costs of recovering, reprogramming, or reproducing any data stored in or used with Parallax products.