8 Replies Latest reply on Apr 3, 2014 6:06 AM by robertwillatt

    Hardware - Using cheap Doppler radar modules

    gdingley

      Hi all,

      I was recently working on a project that required the detection of a moving object, after trying the usual approaches, such as breaking a light beam, I found these cheap radar Doppler modules that are about £4 a piece:

       

      http://www.ebay.co.uk/itm/High-Quality-Wireless-Doppler-Module-Radar-Microwave-Motion-Sensor-/221258031745?pt=UK_Burglar_Alarms&hash=item338401a281

       

      the datasheet can be found at:

       

      http://www.openimpulse.com/blog/document-viewer/?pdf_file=HB100_Microwave_Sensor_Module_Datasheet.pdf

       

      They operate at a carrier frequency of 10GHz and output a Doppler baseband signal, indicating movement. The general Doppler equation is 2*V / lambda, where V is the velocity of the object under detection, and lambda is the wavelength, in this case 300e6/10.5e9 = 30e-3 approx. So for detection of people moving around a room the frequency is quite low, easily sampled with a microcontroller ADC. The output is quite low in amplitude, I had to use an amplification of 53 dB (about Av = 450) , easily done with a couple of op-amps to maintain a reasonable bandwidth.

       

      There are plenty of algorithms that can be used to determine the difference between someone moving around in bed and getting up and leaving the room, I imagine the waveforms would be quite different anyway, all easily executed on a microcontroller.

       

      There are more complicated and hence expensive radar modules around, this one is about £30, but has quadrature detection and FM modulation, resulting in a much richer signal if required.

       

      http://www.rfbeam.ch/products/k-lc5-transceiver/

       

      Anyway, just a few thoughts.

       

      Gavin

        • Re: Hardware - Using cheap Doppler radar modules
          nigeldavidharris

          Thanks Gavin, I think we should think a bit more about in bed detection now. unlike a pir, these will give an output even from small movements in bed. The power consumption worries me but it could be powered on imtermittently.

          I will purchase s module and check it out.

          • Re: Hardware - Using cheap Doppler radar modules
            robertwillatt

             

            Gavin, you suggested the possible use of Doppler radar motion sensors (available on eBay for well under £10 each) as an “in-bed” sensor for Nocturne. I followed this up with some experiments. Output from the module ( a.c. coupled & high frequency filtered) was connected to an instrumentation amplifier.  The amplified signal was connected to a comparator and counter (realised using a Cypress PSOC 4 - System on Chip - development kit). A laptop was connected via USB to the Cypress board.

             

            C code running on the CPU of the Cypress board counts the number of received pulses from the radar module over the integration period (set at 10 seconds). At each 10 second interval the number of counts (in hexadecimal) is passed to the on-board UART.

             

            Results were really encouraging – with a suitably focused module (placed in Aluminium box section) it was possible to detect not just the movement of getting in and out of bed but also some very occasional movement of a person whilst asleep in the bed. I would be happier with reassurance that it is OK pointing the focused radar module at the head of a cared for individual on a regular (nightly) basis.