439 24GHz Radar Presence Detector that Works (LD2410)

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Detecting humans is one of the biggest challenge in Home Automation. Most of us use PIR sensors for that purpose. Unfortunately, they do not detect presence without movement and switch off. Who wants that the TV switches off when you quietly watch a video? Recently, new radar sensors appeared that solve this problem. But they have a slow reaction when you enter the room. Some YouTubers suggest combining such a sensor with a PIR. An expensive workaround. Maybe I found a better sensor for you? Let’s check! Grüezi YouTubers. Here is the guy with the Swiss accent. With a new episode and fresh ideas around sensors and microcontrollers. Remember: If you subscribe, you will always sit in the first row. First: I want to thank all my supporters on Patreon, the guys using “Super Thanks”, and the viewers using my links in the video description. You are awesome! You make it possible that nobody needs to watch an advertisement for a PCB manufacturer. And you are not interrupted by midroll ads. PIR sensors measure the IR emission of warm bodies. As soon as they see movement, they switch the light on. But we all know: If we sit quietly in front of the PC or the TV, the PIR sensor switches off, and we have to wave with our arms to switch it on again. A good laugh for our wives about our newest “invention.” Recently I saw this new sensor: The LD2410 from Hi-Link. It is a 24GHz FMCW Radar. FMCW Radar? Yes, a Frequency Modulated Continuous Wave radar. Standard radars rely on the doppler effect. They transmit a continuous signal that is reflected by conducting materials like metal or water. A moving object shifts the received frequency, as we know from police cars. It is higher when the car approaches and lower when it moves away from us. The frequency shift is proportional to the speed. So, no speed, no signal. The last time we saw such a device was in video #181, where we tried to create a cheap speed meter for cars or bicycles. These sensors are perfect for detecting a human entering a room because they switch in a fraction of a second. Unfortunately, they cannot measure distance other than guessing from the signal strength of the reflected signal. This is unreliable, particularly if persons with different weights have to be detected. As always on this channel, we want more. We want to measure distance with a radar. To do that, we have to use a trick: Extend the “CW” with a “Frequency Modulated” part to the FMCW radar. How does it work? Let’s assume the transmitter changes the frequency with a saw-tooth curve. Because the reflected signal is delayed, the two frequencies are slightly different. Measuring frequency differences is easy and is also known from doppler radars. As you see, the measured frequency shift is now proportional to the distance. Of course, the doppler effect still influences the result. So this method is only accurate for slow-moving objects. Our sensor works on 24GHz. This has two advantages: First, this band is legal and does not interfere with your 2.4GHz Wi-Fi as these cheap sensors from video #135 did. And second, we can build sensitive radars because sensitivity to small movements increases with frequency. Unfortunately, I have no instrument to measure frequencies of 24GHz. But of course, we have one or two aces in our sleeves to find out if they really work on 24GHz. The first is Google. And really, I found the manufacturer of the chip, a block diagram, and a reference design that is very similar to this one. The block diagram confirms that it is an FMCW radar with a saw-tooth modulation. Its output power is 12dBm or 15mW. Not very strong. Hi-Link writes, “Compliant with typical certification standards.” So let’s check if they have an FCC certification. FCCID.io helps find it out. Unfortunately, I did not find it in their database. So most probably, it has no certification. But I found another 24GHz device from the manufacturer of the IC. So they seem to be able to pass an FCC certification at 24GHz, and maybe it is just a matter of time until this sensor is certified. You often find interesting information about all kinds of wireless devices in this database, BTW. And we see that the FCC guys play with expensive instruments. They measured frequencies up to 100GHz… Looking at the block diagram, we see that this tiny chip has digital outputs for a microprocessor. Similar to an SDR receiver. A closer look reveals an MPU on the other side of the PCB. Here I had no luck. Google was no help, and I do not know the type of the MPU. So let's continue with playing Sherlock Holmes. I still do not have an English datasheet. Fortunately, I found some trashy videos on youtube showing a tool to monitor the output. And after some searching, I had the English manual, the English description of the interface, and an English version of the tool. Chrome did not like the zip file of the tool at all. I only was able to download it using Edge. And then, Windows did not like it. But I do everything needed for my viewers, and here it is. I ordered an interface PCB with the sensor. This was a good idea because it not only has a USB to serial chip, but it also has the proper connector for the sensor: Tiny 1.27mm pin headers. Now we have it all on my table, and we can start testing. This sensor is astonishing. It can be programmed with the tool, and the chip keeps these parameters during power down. If properly programmed, you only need to monitor one output pin. If high, either motion or presence is detected. Otherwise, the pin is low. Easy. But how can we program the sensor? The tool has two modes. If you select the correct COM port, tick “engineering mode,” and hit “start,” it shows the output in two diagrams. On the left, “moving,” and on the right, “motionless target.” From left to right, you see eight distance sectors. Each measures 0.75m. The green curves show the selected sensitivity. As soon as the measurement is above one of the green curves, the big button becomes purple or red, and the sensor switches its output pin to high. Obviously, the measurement cannot pass the green line if it is at 100. So, 100 means the sensor does not react in this bucket. With those two values, you can restrict the range of your sensor. Which somehow is similar to setting the green curve to 100 for those buckets. It took me a while till I found out how it works. But now it is pretty handy. I do the testing in our living room because my lab is too small. If I move, the motion part immediately shows movement. The “motionless” is calm. If I stop, the movement part goes away, and the motionless part increases. The distance reading sometimes shows numbers, and sometimes not. It is not very reliable. The curves really move through the buckets when I increase the distance from the sensor. Cool. The radar can measure distance as promised. Let’s test the sensor in the sitting area. I placed the LD2410 on the table in front of our sofa without me watching TV. Here is the reading. Now I place myself in my typical TV-watching position. Here is the result: No movement but presence detected. With these readings, it is easy to fit the green curve so that the sensor can distinguish the two events. How is this done? After stopping the measurement, we enter the thresholds or sensitivities per bucket. The green curves show the entries, and after storing the values, we can remove the sensor from the programming environment and connect it wherever we want. An ESP-01 would be sufficient because we only need one input pin. And the right mounting place probably would be on the ceiling. As a first application, I will use it in my lab to replace my PIR sensor. For good reasons, I want to be very sure before I use it in the living room! Unfortunately, the firmware on the sensor shows some strange behavior. First: If you select 100 to switch off the motion sensor, the motionless part does not work anymore. Second: For longer distances, the output pin does not trigger when the motionless indicator clearly surpasses the green line. Not what I expected. Maybe it is possible to change the firmware in the future to correct these flaws. The readings from the sensor seem to be ok. So, if you write your software, you can modify the trigger processes based on the measured values. I even found a project for an ESPhome sensor that does that. With this project, you do not need the upfront programming. Currently, the project still is a “work in progress.” Another difference to most PIR sensors is the high power consumption. This sensor has to be powered by mains, not batteries. What is my verdict? - This is the best radar sensor for home automation I have seen so far because it combines motion and motionless sensing - The visualization and programming tool is handy - The current firmware does not correctly trigger for longer distances in motionless mode - It is extremely easy to deploy if you can live with the current firmware. Once programmed, you only have to connect one pin, and hardly any programming is needed for the ESP. An ESP-01 with a simple MQTT library example will do the job - The tiny pin header is described as difficult to solder. I had a few 1.27mm pin headers in stock. After cutting a small piece with five pins, I soldered the three needed wires to the female pin header. Now I can check a single module without problems. You can add two more wires to connect the sensor to a USB to Serial converter. Like that, you could save the adapter. RX and TX will also be needed for the ESPhome sensor. - Its price is outstanding if we compare it with other FMCW radar sensors - You also get other 24GHz sensors. I assume they use similar chips but are more expensive. Maybe you used one of those? One last thing: If you do not want to build your own sensor, you can buy this one from Tuya. It has the same module inside. Just the price is different. Because of the outstanding price performance, I assume many more sensors with this module will come to the market soon. This was all for today. As always, you find all the relevant links in the description. I hope this video was useful or at least interesting for you. If true, please consider supporting the channel to secure its future existence. Thank you! Bye
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Channel: Andreas Spiess
Views: 285,637
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Length: 13min 19sec (799 seconds)
Published: Sun Sep 25 2022
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