HB-100 / GH1420 10.25GHz Microwave/Doppler Radar Motion Sensor w/Arduino

I picked up some of these modules out of curiosity, as these modules can detect the motion and speed of objects through walls or other non-metal obstacles.


Overview:

The modules themselves are fairly simple in use, since they output a signal with the frequency/pulse width indicating the speed, and the amplitude/voltage indicating the strength of the reflected signal.

The speed is very simple to calculate once the frequency of the incoming signal is detected:

km/h = hz / 19.49
mph = hz / 31.36

These HB-100 modules require a pre-amp circuit to boost the IF signal, so I used an LM358N and the circuit at https://hackaday.io/project/371-hb100-radar-shield to boost the intermediate signal.

The output of the circuit sits at about 2.5v when quiet, and moves up & down to represent the received AC waveform.

In pure digital form, this would be very easy to detect using interrupts, but with an amplified analog signal, weaker signals may be missed.

Problem:

Tests with this radar shield using standard frequency counters/libraries seemed to show that interrupts and edge-detection have limited sensitivity to weak signals. They also provide no means for detecting the amplitude of the signal. It seemed that using the on-board ADC may provide better results in this frequency range. (0 to 4000 Hz or 0 to 205km/h)

Goal: 

Detect the frequency and amplitude of low frequency (0-4khz) signals from HB-100 modules, while potentially increasing the sensitivity of waveform detection using the HB-100 & circuit as linked above.

Result:

The resulting code uses the Arduino ADC to sample incoming signals using very simple peak-to-peak detection.

Signals are detected when the waveform transitions above or below a set "midPoint" which represents the 0v value of the AC waveform. Typically, it will be ADC_RESOLUTION / 2.

This is very similar to the edge detection used for interrupts and digital signal detection, but using the ADC to detect weaker transitions.

ADC Resolution / VCC == Volts per Increment ( 1023/5v = 0.005v )
Sensitivity of 10 == peak-to-peak detection of +/- 0.05v signals


Technical Info:

The ADC is driven in free running mode, taking samples at about 38.5khz while looking for specific deviations in the measured voltage that correlate with a peak-to-trough waveform.

The results are summed in a single variable, and returned either as a single result, or an average, depending on how often the results are read in relation to the received signal.

Information about the signal, including frequency, amplitude and number of samples allows more complex analysis.

Conclusion:

The code was developed in a very short time, and can still be considered a work in progress, although it seems good as-is. It tests well up to about 2-4khz with another Arduino producing square wave output. When used with the radar module, it is very sensitive, and allows the sensitivity of the device to be defined in software, and/or results to be filtered.

Code & Examples:

https://github.com/TMRh20/AnalogFrequency

RF24Audio Library Released:

 Wireless Digital Audio Streaming and more with Arduino and NRF24L01 modules

  Its been a little while in the making, but I am finally releasing my RF24Audio library. The library offers a number of features, mainly the ability to wirelessly stream realtime data or audio captured from an analog input to one or more other devices. 'Other devices' can include Arduinos, PCs, or any other device capable of reading the data stream.
  Since the library utilizes the core RF24 radio library, advanced usage and customization can be configured, and allows interaction with audio devices in a number of different ways. The TMRpcm audio library (WAV audio from SD card) has been updated to support the RF24Audio library as well, being capable of multicasting audio to a number of devices. A demonstration of this interaction is shown in the following video:

  The library is designed to be very easy to setup and configure, just connect a radio module, microphone and speaker. External buttons are optional, and are managed internally by the library. This can be disabled to allow further customization via keypads, etc. Users can also utilize the core RF24 library to interact with the audio devices in a number of ways, including capturing audio streams and feeding the data to a PC.

Features:

• User friendly setup and configuration: For beginners too: Just connect a radio module, microphone, and speaker. The library handles the rest.
• Recording and broadcasting of audio to multiple devices using only Arduino, RF24 modules and input/output devices (speaker,microphone)
• Multicast: Enables broadcasting to all nodes, single nodes, or partial groups of nodes
• External controls: Use external buttons or code to control audio streaming
• Volume control: Use external buttons or code to control audio volume on receiving devices.
• Remote control: Start recording remotely via radio commands (Currently cannot stop remote recording)
• LED Indicator/Visualization: Indicates audio playback and amplitude.
• Customization: Using the underlying RF24 core library allows custom interaction with audio devices running this library. Receive audio data and stream it to a PC over USB, create and broadcast computer generated audio in realtime, and more! See the USB_Audio example for more info.
• Create additional node groups: Allows nodes to join private broadcast groups, and multicast only within their group as desired

Pin Assignments:

• Speakers: Arduino Uno,Nano,etc: pins 9,10 Arduino Mega: 11,12 (Timer pins cannot be changed, but can use 1 pin and ground)
• pin A0: Microphone/Input pin
• pin A1: Transmission/Recording Start pin
• pin A2: Volume Up
• pin A3: Volume Down
• pin A4: Trigger remote recording (Only working with dual devices)
• Cannot be changed: LED Pin: Uno,Nano,etc: pin 6 Mega 2560: pin 13 (main LED pin)

Links:
Library Documentation
Download

Source Code:
RF24Audio Library
RF24 Radio Library
TMRpcm Audio Library