Homemade Motion Sensor

This is an extension of my project for Homemade Environment Sensor. The sensor is now expandable. I am creating a new thread to share on how I extend the sensor.

This week, I just got shipment for a motion sensor. There are a lot of discussion about PIR based motion sensor. I would like to share my experience with microwave radar based sensor. The product id is RCWL-0516. You can search it on Ebay or Aliexpress. They can be purchased for less than one dollar. Here is how it look like.

This kind of sensor typically have 360 degree coverage. It also does not need line of sight. This is could be an advantage for right application.

Here is a short demonstration.


I also have a good old PIR sensor. It is hc-sr501 motion sensor which also available in Ebay and Aliexpress for less than one dollar.

This sensor is really hard to use in outdoor environment. It has a lot of false positive due to cloud and sun.

So, I combine the hc-sr501 & RCWL-0516 like below.

The PIR sensor is the primary detector in this case. When it detect a motion, it will enable the cds pin on RCWL-0516. At that point, if RCWL-0516 detect a motion as well, then the vout pin on RCWL-0516 will output a binary one to indicate a motion. Doing this will reduce the false positive when you use a PIR sensor outdoor.



I just recently received a shipment of 5 of these RCWL-0516 microwave motion sensors. I am planning on using them with my HubDuino project to see how much more reliable they are than the often flakey HC-SR501 PIR sensors.

Thank you for keeping us posted on your progress!

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Hi Dan,

I just want to share what I learn about these motion sensor so we all can build a better one. I hope you can share your experience as well.

Each type of motion sensor has its own quirk. The RCWL-0516 has its own advantage which can be consider disadvantage. 360 degree feature, potentially an issue when you live in an apartment. I may detect motion in your area as well as your neighbor. This is why also brought up the combination with SR501 . SR501 can give you direction where to look at.

My goal is to learn how to use them for appropriate scenario and combine them with some other sensor to get to the right application. I hope we can learn together.

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I was actually considering testing them to see if they can reliably detect moving objects through ceiling drywall. This would allow me to add these throughout the second story of my house (in the attic, facing down, between the insulation and on top of the ceiling below) with no visible wires and no batteries to ever need changing. It would make automating the house much more seemless, as lighting automations would work almost like magic as you walk around the house. If these sensors work well, I just want to make sure they are very safe as I would not want to cause a fire in the attic!


In case fire does happen up there, this sensor can help you to catch it early.

I had a video to demo it.


Good to hear your voice describing what we are seeing. Those look like they can come in handy where typical PIR is inappropriate.

Thanks for sharing Iman!

Maybe using metal shields around the sensor to create dead zones could help with unwanted detection?

I did a little testing today. I am amazed at how well these work through walls. However that’s not always a good thing! :wink:

Unfortunately, it seems prone to false alarms. There is no one home right now, but it is changing states regularly.

I have not seen false alarm yet. However, I saw in youtube that RCWL-0516 detect movement body of water (human or non human),. If you have moving water, it is possible to generate false alarm. This is why I experiment combining the pir and rcwl-0516 is a way to reduce false alarm.

This is an interesting suggestion. I will give it a try.

No moving water anywhere in the house. But, I wonder if it is detecting the spinning fans in my desktop pc that is nearby? I’ll have to do more testing to be sure.

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The radar is based in Doppler effect. I do not want to go into the detail of the theory. The reflected signal information has frequency value that translatable the speed of detected moving object. I think the maker of RCWL-0516 has filter out movement that does not look like a human. Assuming the fan rotation is observed by the sensor, the speed, it move, should be outside the range of the filter.

This is interesting. Let me know if you learn anything about the fan. I will watch mine.

Microwaves are great but also a pain if you can't adjust there sensitivity for the room. We use them /make them all the time for work and they will go through plasterboard walls and windows. They will also pick up a fan 100%, we also have a site that they keep false triggering because the building isn't built well so is drafty!

I'm going to ask if they would be willing to make a ZigBee or z-wave 12V version at work :slight_smile: . If they do then we could make a directional microwave or PIR as well as a 360 microwave or PIR. Would this be of interest to anyone?

Actually, if you are willing to go to the analog signal, you may be able to solve the issue. However, the math will be much more complex.

The Doppler frequency return can be read as analog signal. Using something like,


That analog signal can be converted to frequency domain. That will allow you to better identify the object you are interested on. There are a lot of signal processing trickery that you can do at that level. I do not want to go that direction at this point. The MCU does not have enough cycle to do this and other stuff at the same time. However, for those who need much more detection accuracy, there is a path to do so by processing the signal into frequency domain and look into things there.

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I have a question about this sensor. I would like to have a real occupancy sensor more than a motion sensor in order to let ligths on also when someone is just sitting watching the television , reading a book o typing a pc keybord, that is with little o near no motion at all. Is this feasible with this technology, better than with a PIR sensor? Is it street available on zigbee sensors?

Microwave Radar and PIR detect movement (not static object).

Combining the 2 sensor is to make the detection better in handling false positive. It is not for the purpose of detecting non moving object.

Combining PIR and Microwave is known solution. If you look to outdoor PIR motion sensor, big brand like Bosch and DCS has microwave and PIR combined sensors available for sale.