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$1.40 Microwave Radar Sensors — Parallax Forums

$1.40 Microwave Radar Sensors

ercoerco Posts: 20,256
in General Discussion
Are you kidding me? Just heard about them here and ordered three.

http://www.ebay.com/itm/112160912972

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Comments

  • Heater.Heater. Posts: 21,230
    Interesting. A kind of ping module with radio waves.

    No directional capability.

    Perhaps that can be fixed by building it into suitable dish/reflector.
  • ercoerco Posts: 20,256
    edited 2017-03-19 21:49
    $5 module operates at 10.5 Ghz: http://www.ebay.com/itm/171907161731

    What little info I found on the original lfs-dc04 module says that it has an omnidirectional range of several meters. Output goes high for 30 seconds when triggered by motion, like some PIR sensor modules. I found a Youtube video with an offensive start so I won't link here.
  • ceptimusceptimus Posts: 135
    I have some of the second kind linked to by erco. They do seem to be directional and seem to respond best to things approaching or retreating from them. However, be warned that the output level is very low and quite noisy, so to be useful as an input to a typical microcontroller A/D you need to add some op amps to filter/integrate/amplify the output signal.

    I think their intended use is automatic door opening sensors - they are mounted up over the door and can 'shine' through plasterboard or similar - they sense, typically, people walking in the vicinity of the door so that the door can be triggered to open.

    Maybe the cheaper omnidirectional ones (which according to the write up do have a high level output) are intended to turn on lights when people enter a room or similar. The fact that they have a cadmium sulphide light detector built onto the board makes this likely - so that the lights need not be switched on if there is already daylight in the area. Looks like they may be a radar alternative to the more normal passive IR sensors used to switch on porch lights and similar.
  • MikeDYurMikeDYur Posts: 2,176
    edited 2017-03-19 22:36
    Got a quick explanation of how these work, is it anything like the X-Band Motion Detector? I haven't found the appropriate application for the one I have. It supposedly can sense through walls. But I have tested the distance, and it had no problem at 30 feet(LOS).
    At first glance, I don't understand the need for the photocell, STOP



    EDIT: Well I'm glad someone else asked first.
  • Cluso99Cluso99 Posts: 18,069
    edited 2017-03-20 04:19
    erco,
    You are not being as thrifty as usual.
    Here is one for $1.01
    http://www.ebay.com/itm/LFS-DC04-2-7GHz-Microwave-Radar-Module-DC-5V-360-Degree-High-Level-Signal-Output-/311713408338?hash=item4893912552:g:ffUAAOSwpLNX9p15
    or if you want to solder the LDR yourself to save a cent ($1.00) then here
    ebay.com/itm/LFS-DC04-2-7GHz-Microwave-Radar-Module-DC-5V-360-Degree-High-Level-Signal-Output-/182419142635?hash=item2a790737eb:g:AoQAAOSw2xRYd1Vw

    BTW, Iam wondering about the LDR too. Could it be used for the aerial perhaps???
    Postedit: Google is your friend. It is an LDR and only works during the dark.
    https://youtube.com/watch?v=lr9HxnSiLig
    Remove the LDR to work day and night - so the $1.00 is the easiest to use!!
  • ercoerco Posts: 20,256
    You almost had me at "thrifty", Cluso!

    $1.01 plus Shipping: $1.85 ePacket delivery from China

    or for the DIY LDR version:

    $1.00 plus $2.00 ePacket delivery from China

    But I'm distracted playing with my first ESP8266 so I might be slipping.

  • Cluso99Cluso99 Posts: 18,069
    Ooh!
    Both are free shipping to Oz :)
  • RS_JimRS_Jim Posts: 1,764
    I have a question. What do cars use that have Dynamic Cruise control use for a distance sensor? It would seem to me that it would have to be some form of radar.
    Jim
  • ceptimusceptimus Posts: 135
    Most do use radar. Subaru has a system that uses two cameras giving depth-perceiving binocular vision.
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2017-03-20 17:04
    These are S-band range detectors of the type your local supermarket uses to automatically open the doors for you when you approach. So if you had a use for the X-Band Detector Parallax sells, this will fill that bill. Parallax's has a sensitivity adjustment, which I'd think would be handy.

    The photocell is probably as a safety for use in door opening/closing schemes. Kirk and Spock would have appreciated these on board the Enterprise for when the doors didn't work right. Technology of the 23rd century was a little lacking.

    You could probably make a focusing cavity for one of these, but you'd need to get the numbers right for any hope of it working.

    Oh, and I suppose you could use these to make cameras. Just a thought.
  • ercoerco Posts: 20,256
    RS_Jim wrote: »
    I have a question. What do cars use that have Dynamic Cruise control use for a distance sensor? It would seem to me that it would have to be some form of radar.
    Jim

    I tried to build a cheap long-range collision avoidance system with a simple bump switch on a 200-foot bamboo pole ahead of the car. Worked fine on the freeway but it kept fouling in city traffic.

  • Cluso99Cluso99 Posts: 18,069
    erco wrote: »
    RS_Jim wrote: »
    I have a question. What do cars use that have Dynamic Cruise control use for a distance sensor? It would seem to me that it would have to be some form of radar.
    Jim

    I tried to build a cheap long-range collision avoidance system with a simple bump switch on a 200-foot bamboo pole ahead of the car. Worked fine on the freeway but it kept fouling in city traffic.
    ROFL
  • GordonMcCombGordonMcComb Posts: 3,366
    Ah, I see now what the CdS cell does. Following the link Erco gave at the start, one of the posters says these are for nighttime security lights that use radar instead of PIR, and the photocell prevents triggering during the day.
  • ercoerco Posts: 20,256
    More useful info from that other forum:

    The GHz oscillator uses PCB tracks to make the necessary inductors and capacitors, so it's frequency is neither precise or stable, but that doesn't matter. The original purpose for these modules is controllers for room lighting, so there are lots of them, and they are cheap.

    A really cool attribute is that they can be mounted inside a plastic box, with no lens or window needed. Great for hidden detectors.

    Here is a write up :
    https://github.com/jdesbonnet/RCWL-0516/

    and if you want a different shape :
    http://www.ebay.com/itm/1PCS-LED-3-1...UAAOSwIgNXjfD7
  • GordonMcCombGordonMcComb Posts: 3,366
    erco wrote: »
    More useful info from that other forum:

    The GHz oscillator uses PCB tracks to make the necessary inductors and capacitors, so it's frequency is neither precise or stable,

    Ah. So not really "legal" to operate in this country. Not sure how much variance the FCC allows for S-band, but parts are used for broadcast, so there probably are limitations. A few thousand Hz probably wouldn't hurt much, but inching down toward 2.4 GHz will screw with a lot of cordless phones. And I know you still use those in the Erco household...
  • ercoerco Posts: 20,256
    "It's frequency is neither precise or stable" = Poor man's "spread spectrum"
  • localrogerlocalroger Posts: 3,451
    If these sensors are triggering on motion they are almost certainly triggering on doppler returns rather than time-of-flight; they mix the echo with the carrier and if they get steady beat frequencies in the right range, the output comes on. I've seen roadside truck sensors that work like this. It's a much simpler principle than time of flight, but doesn't give distance info, only presence and movement (and maybe velocity) within the detection envelope.
  • ercoerco Posts: 20,256
    localroger wrote: »
    It's a much simpler principle than time of flight, but doesn't give distance info, only presence and movement (and maybe velocity) within the detection envelope.

    Hey, for $1.40, simple rocks!

  • xanaduxanadu Posts: 3,347
    Let's say I had this on the rover, and the rover was moving slowly. Would it only detect people, or would the rover's movement set it off?
  • ercoerco Posts: 20,256
    The latter, I believe. AFAIK this operates like a PIR sensor where it takes a few seconds to stabilize a reading, then looks for changes in that reading to "detect motion", so it needs to be stationary.

    From what little I can gather.
  • kwinnkwinn Posts: 8,697
    It is a form of doppler radar. See https://en.wikipedia.org/wiki/Doppler_radar for a description. The frequency of the output is proportional to the velocity of the object being sensed.
  • skylightskylight Posts: 1,915
    kwinn wrote: »
    It is a form of doppler radar. See https://en.wikipedia.org/wiki/Doppler_radar for a description. The frequency of the output is proportional to the velocity of the object being sensed.
    So add a laser,a QS,some sights and perhaps a little more range and you have a speed trap gun?

  • kwinnkwinn Posts: 8,697
    skylight wrote: »
    kwinn wrote: »
    It is a form of doppler radar. See https://en.wikipedia.org/wiki/Doppler_radar for a description. The frequency of the output is proportional to the velocity of the object being sensed.
    So add a laser,a QS,some sights and perhaps a little more range and you have a speed trap gun?

    Just needs more range, better focus, and possibly sights. Most old radar units did not have sights, just point and ticket.
  • ercoerco Posts: 20,256
    Just got mine, I notice they changed from the CdS cell in the Ebay ad to a clear flat top LED or phototransistor. I like how they angle two resistors (outlined in yellow) on assembly to modify the circuit. Need to test.

    CAM00161.jpg
    CAM00161.jpg
    1250 x 650 - 208K
  • macrobeakmacrobeak Posts: 354
    http://hackaday.com/2017/03/31/the-right-circuit-turns-doppler-module-into-a-sensor/
    Here is a nice breakdown and enhancement hack for cheap radar modules.
  • Duane DegnDuane Degn Posts: 10,588
    erco wrote: »
    Just got mineNeed to test.

    Me too. Three of them arrived today.
    erco wrote: »
    Need to test.

    Me too. Now why did I buy these?


    macrobeak wrote: »
    http://hackaday.com/2017/03/31/the-right-circuit-turns-doppler-module-into-a-sensor/
    Here is a nice breakdown and enhancement hack for cheap radar modules.

    Interesting stuff. Thanks for posting the link.

  • ajwardajward Posts: 1,130
    edited 2017-04-11 13:36
    erco wrote: »
    $5 module operates at 10.5 Ghz: http://www.ebay.com/itm/171907161731

    What little info I found on the original lfs-dc04 module says that it has an omnidirectional range of several meters. Output goes high for 30 seconds when triggered by motion, like some PIR sensor modules. I found a Youtube video with an offensive start so I won't link here.

    Yeah... I ran across that one too. How rude! :-| (And that was the only one I found. Seems simple enough tho'.)

    @

  • xanaduxanadu Posts: 3,347
    I have the white module, what are the 2 jumpers for?
  • ercoerco Posts: 20,256
    xanadu wrote: »
    I have the white module, what are the 2 jumpers for?

    You mean how those two SMT resistors could have been soldered on two ways or left off?

    Probably to adjust for different DVD regions, NTSC vs HDMI vs UCLA.

  • xanaduxanadu Posts: 3,347
    edited 2017-04-25 18:43
    I removed the light sensor and they work great,
    erco wrote: »
    xanadu wrote: »
    I have the white module, what are the 2 jumpers for?

    You mean how those two SMT resistors could have been soldered on two ways or left off?

    Probably to adjust for different DVD regions, NTSC vs HDMI vs UCLA.

    Sweet, I needed PAL, pal.

    I removed the light sensor and they work. I setup a cheap PIR detector alongside, and the PIR is much more sensitive.

    It doesn't seem to detect anything moving very slow, unless it's right in front of sensor. That is interesting to me, because if it were on a slow robot, it could provide motion detection (things moving faster than the robot) while the robot is moving. That's something not many sensors can do, so I'm going to explore that some more.

    It's hard to see the traces on the board, but I have the datasheet for the chip and will try to figure out the jumpers.

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