Quick Look: Microwave Motion Sensor

[@nigeljohnson9820]

I have recently found a very good reason for using a combination of PIR and radar detection modules in alarm systems. During the summer heat wave in the uk all PIR sensors stopped working, the reason being ambient air temperature had reach human body temperature 98.4F, making the IR from humans and other mammals invisible against the radiation from the background. The big weakness with these microwave modules is that they have a very poor front to back ratio. Meaning they can be just as sensitive to movement behind them as in front. I do not know if this is true of all versions on the market, but it is true of the few I have use. I have had some success mounting them in metal boxes fitted with a plastic lid. The lid being transparent to the microwave signal, while the metal box shields/focuses the beam in one direction. I have found the standoff distance from the back of the box is important to maintaining a good front sensitivity. I assuming that the radiation reflected from the back plate form a standing wave that may be constructive or destructive, depending on distance from the plate and operating frequency. There maybe a reliability issue using this technique give the poor stability of the microwave frequency.

[@mtkoslowski]

Nigel Johnson : As a side note, it has been an objective in order to minimize false alarms on security systems by digitally ANDing the alarm output stages with IR and microwave intruder detection.

[@nigeljohnson9820]

@@mtkoslowski I have designed a system that allows select and AND/OR as options between PIR and radar inputs. While AND might help avoid false triggers, in hot weather the PIR will disable the alarm output. Most PIRs used to control drive way lights are disabled during daylight hours by an LDR sensor, even if the PIR provides an alarm outputs. I think part of this is because sun light heating of the surroundings can blind the PIR, making its alarm output unreliable in sunlight. ( Thinking about this, there may be a good reason for fitting an ambient temperature sensor in the alarm sensor, then the decision as to the combination of radar and PIR outputs can be based on the ambient temperature. Maybe my next alarm project will try this.)

[@ronen124]

@@nigeljohnson9820 the difference in ambient infrared radiation on a hot summer day when a human body passes nearby adds a small factor to the total and makes it harder for the internal uC to decisively put out a logical signal whilst at night there is much bigger difference at the same occasion

[@nigeljohnson9820]

@@ronen124 I thought I had already said that. PIR detectors work by detecting the change in IR within their field of view. A faceted Fresnel lens in front of the detector is used to maximise the gradient discontinue in detected radiation. When the ambient temperature is close to body temperature, the body becomes invisible to the PIR sensor, as it screens the background radiation while replacing it with body radiation at the same temperature. This is like trying to see a white artic fox against a background of fresh white snow. The more sophisticated PIR detectors may use a micro processor to detect and minimise false triggering, but the circuitry of most PIR detectors is far less complicated, either using a dedicated analogue PIR IC or a simple opamp or comparator configuration to process the AC signal generated by the PIR sensor. A common configuration is to feed both inputs of an Op-amp from the sensor output. One input is low pass filtered the other is high pass filtered. The Op-amp output nulls out the sensor DC component while amplifying the AC component. This arrangement is slightly more complicated than simply AC coupling the detector amplifier to the sensor, but makes it slightly easier to detect the relatively slow changes associated with a body intrusion while still rejecting the very slow changes associated with ambient temperature changes. The op amp output is converted to a digital signal using a Schmitt trigger or monostable configuration usually using elements from the same IC package. All can be done with a single quad Op-amp or quad comparator IC package, though an OTP microcontroller circuit can be just as cost effective provided that it supports analogue inputs, e.g. ADC or comparator inputs. ( I remember an project article from an electronic magazine of the 70s or 80s. This had an optical alarm sensor constructed from a bridge circuit of photo transistors. The sensor was placed at the focus of a simple convex lens. The idea behind the circuit was than movement in the field of view of the lens would unbalance the bridge and produce a detectable output, much like that of a PIR. Since the idea has not been pursued commercially, I must assume that it did not work that well. However many CCTV security systems have the facility of producing an alarm output when consecutive stored video frames detect cumulative differences on a pixel to pixel comparison basis. This effectively detecting movement between video frames.)

[@ronen124]

​@@nigeljohnson9820 I guess you did said that I just repeated it with different words from my own experience with PIR modules. The module itself uses its uC to "learn" the surroundings so that the changes will be due to the last minutes/seconds, that's why when you stand near an automatic opening door long enough it will think that you become the ambient reality and it ignores you hence the door closes while you are there. I would like to share a small and simple tip against false PIR triggers: there are a lot of destructions from the sides of the module that let (for example) a door be opened while no one around as if an invisible ghost just hovered there or, with my setup, beeps when nobody passes. that happens when a car passes by or the IR radiation perculates from other passing objects, to avoid that I install a small plastic "tunnel" on the Fresnel lens that allows the light to come only from the front - this helped me a lot. cheers

[@bblod4896]

I like the tiny antenna. Wish HF antennas were that small. Thanks for the look, have a great week.

[@nigeljohnson9820]

In mobile phones the practical length of the aerial has been reduced by making it from a dielectric material in which the velocity of em waves is significantly less than that in free space. it was this that allowed mobile phones to evolve from the early versions that had short stub quarter wave aerials protruding from the top of the phone case.

[@bblod4896]

@@nigeljohnson9820 Doesn't the higher frequency also contribute to a smaller antenna?

[@nigeljohnson9820]

@@bblod4896 it most certainly does, I have not seen any dielectric aerials below microwave frequencies. At 800MHz the 1/4 wavelength is approximately 9cm, even using a helical aerial this is going to be a lot bigger than a dielectric equivalent.

[@billsquires79]

This is awesome...but would like to connect a buzzer to it.as well as an led. Any help would be appreciated.

[@ernieh5664]

Hi could you tell me the approximate range and sensitivity of the circuit, when you move an object toward it please. Thanks. Ernie.

[@jameswest3890]

Will the unregulated output be the same voltage as the input?

[@prasadshettigar3703]

I have experienced,the microwave sensor is not giving response 360 deg.One side its sensitivity is more and another side less.How to resolve this issue

[@petermoritz2452]

Dose these interfere with one another? I got an application where I woul need a bunch in close proximity. But it's important that they don't set of the neighboring ones.

[@MCsCreations]

Really interesting design, dude! Pretty impressive! 😮

[@tetraliteproducts542]

No LED series resistor needed. There's a 100ohm series resistor on board on the output. Data and schematics for the chip (RCWL-9196) and the board (RCWL-0156) can be found here: www.mpja.com/download/34685MPData.pdf www.mpja.com/download/34685MPSche.pdf www.snapeda.com/parts/rcwl-9196/RCWL/datasheet/ These documents also show some options that are available on the board for adjusting range, trigger cycle time and light sensitivity (if using with a photoresistor).

[@milesmoore5422]

And what do we do with it ? What is it good for ?

[@tamojitsaha1128]

Is this radar sensor sensitive for birds flying by or more sensitive to human?

[@KarlA-vk4kn]

Hi Paul I was looking at this on Ebay yesterday and after seeing your video I'm impressed enough to buy one. Thanks for the description 👍🙂

[@christiannielsen3863]

What is the motion detection range and what material will be detected?

[@learnelectronics]

The range is about 7 meters and they are for human detection.

[@neuixinyee2348]

Can the microwave motion sensor be modified to only detect moving vehicles?

[@mike99191911]

Excellent Video Paul. Is this more powerful than the typical motion sensors you get with an Arduino starter kit?

[@learnelectronics]

It has a longer range, about 7 meters.

[@mr.bianchirider8126]

Great video. I purchased a few of these a year ago and couldn't get it to work very well with a Node MCU. I'm wondering if the wifi causes some interference.

[@frankhobsonKJ4CDM]

They are very sensitive to movement. On wifi interference, no. I made a flashing led motion detector.

[@learnelectronics]

Could be. I didn't see any notices about wifi, but yo never know.

[@ttssoon1975]

Yes. It is definitely influenced by ESP8266 wifi. I had made one which very near each other causing false triggered in RCWL-0516. You need to keep each other away about 10cm to keep the radar sensor work properly.

[@bblod4896]

I wonder if the brake and lane sensors on vehicles use that system.

[@learnelectronics]

I dont know.

[@BrucesWorldofStuff]

Thanks Paul, great video! I'm going to head to Amazon and get some ordered for a project that I am working on for lights in my kitchen and I think this will work better that what I was going to do. The LDR part will fit right in with what I am doing and work great for my 3 month old project... Hmm that is still setting over there..... LOL

[@whitehoose]

They are truly part of the black arts. Don't know where Paul intends to take this - so don't want to steal his thunder. For ppl just starting out with them - the antennae is quite directional and so I'd recommend using 90deg connecting pins so the unit will sit up on the bread board vertically (narrow end up) which will make it more responsive to movement. Also note when you power on the board it takes about 10 seconds to "warm up" in two phases. If you connect a LED to vout & gnd (consider using a transistor or mosfet as a switch to help beef up power switching capabilities) - the onboard switching is pretty lightweight so only small loads. You can get away with a single LED + 100ohm resistor OK. i1150.photobucket.com/albums/o618/doppleganger1/mosfet%20switch_zpsacvh98lo.jpg - cct from big clive When you power on, the LED will come on for 2-4 seconds ... then it goes off and stays off for about 6 seconds while the radar warms up (just long enough to wonder what's wrong!). Then the detection settles and it should start responding to movement. There are pads on the opposite side c-tm, r-gn used to adjust (re)trigger time and sensitivity (distance). Pad Function C-TM - Regulate the repeat trigger time. The default (unpopulated) time is 2s. (10nf on main cct board) add 100nf to pad = 33 seconds (use SMD capacitor to extend the repeat trigger) Pin 3 of the IC emits a frequency (f), and the tigger time in seconds is given by (1/f) * 32678 R-GN - The default detection range is 7m, adding a 1M resistor reduces it to 5m

[@williammiller7543]

Good Video, very informative. Do you just wire in LDR to make it work at night only?

[@learnelectronics]

correct

[@RespawnRestricted]

Great vid.. do you still live near Pittsburgh? I wanted to make u a grab bag type box. but had some questions do yo have a email or something ?

[@mtkoslowski]

Paul, how do you achieve directional output? Don’t microwave sensors need a horn? What is the range of this sensor and what are the applications for this board?

[@learnelectronics]

7 meters, directional to front of board, human detection

[@mduntr7503]

Damn, the antena is what gets me, nice...

[@timwsac]

Thats a skuoocome little board Paul I am going to have a couple for sure

[@IvanColmenero]

That's nice and interesting motion sensor... by the way, the Steelers win yesterday sunday night football. Congrats!

[@michaelpadovani9566]

Neat little module

[@RFADICTOS]

Excelente proyecto amigo muy interesante el proyecto haré las pruebas!!!!

[@learnelectronics]

gracias

[@pulesjet]

Not sure why but I want one. LOL Live in the boonies. Would be nice knowing when someone is pulling into our rather long drive way. Look at Micro Wave as the Transition between RF and Light Radiation. Microwave behaves a bit more like light then Radio Frequencies

[@mtkoslowski]

pulesjet : Please consider a buried ground loop antenna, and when a large ferrous mass disturbs/shifts the oscillator you can detect it. Circuits available on the web.

[@danielheide6574]

I snuk through five acres of motion sensors one night. People say that it's immpossible but I beg to differ: Doing my Ninja sneak Just happens to be at one meter per second so then to cross arms putting the palms against the shoulders creates a magnetic loop because of your hand vortices Then matching the speed of light in hyperspace I simply slipped out of dimension and walked through.

[@learnelectronics]

seacrest astronomy No more secrets

Right.👍👍👍

[@NewAgeDIY]

Can you make a working demo. Something that shows this unit in action. Would order in the board if I can see what it could offer. Thanks for sharing ✌🏻

[@learnelectronics]

I did. I waived my hand in front of it and it turned the LED on. That's all it does. It detects motion and sets the output high.

[@NewAgeDIY]

learnelectronics / sorry I didn’t realize it was that simple! I’m interested, so I’m off to buy one. It appears that your channel is going to keep me busy 👍🏼 I’m now going through your video library and just now discovering lots of great ideas and further projects for me to work on. I’m glad to see that you’re very active and making new videos. Thanks for sharing and I will see you in your next video 😃

[@isoguy.]

Awsome

[@jamest.5001]

So does the microwave have to be on to be detected? Ha-ha!

[@VideoStefan17]

peace! :)

[@bud03038]

Great video! de WQ1I

[@jclowersitc4866]

Made a bunch of these with the transmitter and a receiver.

[@ronen124]

can you tell what is the range of detection for human body for such a module?

[@jabhomemonitoring]

@@ronen124 I toyed with one today, and found it to be a good ten to fifteen feet.

[@ronen124]

@@jabhomemonitoring fair enough, thanks. I have to check it as a PIR detector replacement for a future project

[@jabhomemonitoring]

@@ronen124 I've read that the 3.1 gig that it emits can interfere with other sensors of it's kind. Plus, I don't know how you feel about increasing the high frequency radiation in your house....... my home monitoring blankets the area with motion sensors, both inside and out. I've yet to determine if they interfere with each other, but my plan so far is to use these for outside and the yard, and ir for the inside. They should be great for cars rolling down the driveway, and I am going to try putting them underground also. Probably just two to three inches.

[@ronen124]

​@@jabhomemonitoring I doubt if it emits more microwave radiation than a cellular phone at rest (not while talking which is way higher) more than that it will rest in a place where not many people pass and a PIR detector cannot do an honest job during daytime under the sun - there are far too many false alarms.. Putting those underground protected from moist should be a good idea, at this notion I would want to check their behavior underwater as well - you can never know what interesting project will be necessary to tinker with tomorrow..(-:

[@zjoe555]

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