Lately, many radar sensors have become available
for relatively cheap prices. In this video, I will give you an overview of what is
available and how they compare. And, of course, we will have a look into how they work and test
a few of them. After viewing this video, you should be able to choose the right sensor for your
needs. And you should know which are overpriced.
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Over the years, we got a few iterations of
radar sensors. Some of them were very cheap, but most of them were quite expensive. This
changed with the arrival of new radar chips for 24GHz and 60GHz. So, today, we will:
- Look what radar sensors can measure and how they do it
- What kind of sensors we get
- How they compare
- Do some testing
- Check the integration in Home
Assistant or other applications
- And finally, you get my verdict
Radar is the abbreviation of “radio detection and ranging”. It was very important for the outcome of
World War II, where it got a huge push when cavity magnetrons were invented by the British who shared
them with the Americans. These high-performance tubes enabled the building of strong transmitters
for very high frequencies. The high frequencies were needed because the resolution of a radar
heavily depends on its frequency. And the high power was needed because they wanted to
detect far away and small airplanes.
Radars emit signals and listen to
the part reflected by conductive material such as metal or water.
Because they use directional antennas, they can detect from which direction a signal
is reflected and how strong. Early radars just showed the presence of an object. Later, they
used the Doppler effect to determine its speed. Fast-moving objects reflect the signal
on a higher or lower frequency, similar to a passing police car. The bigger the frequency
difference, the faster the object. Unfortunately, it was not possible to measure distance
exactly until another invention was made: FMCW radars. They change their frequency at a
rapid pace. This frequency change has the effect that it not only shows the speed of the plane but
also its distance. Unfortunately, both signals are mixed. So, the distance of fast-flying planes
is not accurate. Still, the results were usable.
Our new radar modules are based on the same
principles: They transmit on a high frequency, receive the reflected signal, and make
some calculations. Some radars can only show the speed, others the distance,
and the more sophisticated, both.
Let’s have a look at the different
generations of such sensors.
The first sensors covered on this channel
were these two: one runs at about 10GHz, the other at 24GHz. Both were Doppler radars
and provided an audio frequency proportional to the speed of the detected object. While
the first was hardly working, the second was able to detect the speed. We tried it for the
detection of bicycles, but we were not able to get more than a 5-7m range. Fortunately, one of
my viewers, Mathieu from Limpkin, kept trying, and here we have a small device consisting of a
radar module, a sensitive amplifier, and an STM32 MCU. He did a marvelous documentation if you are
interested in how he built it. In today’s video, it is one of the few sensors outputting speed. You
get sensors with longer ranges, but unfortunately, they are still much more expensive.
24GHz is a so-called ISM band that can be used by everybody without a license
as long as the device complies with the regulations. 10GHz is no ISM band, BTW.
On this module, we see the typical antenna arrangement: A set of transmitting and a
set of receiving antennas. A rule of thumb: The bigger the antennas, the more directional
they are. So, the range becomes longer, and the detection angles get smaller.
These modules were quite big and extremely simple. As Shahriar form “The Signal Path” showed, the
frequency of those sensors is very unstable, and for sure, they cannot be certified by authorities.
So we need something better. And smaller.
When Smartphones started to include all
kinds of sensors, they were produced in high quantities for cheap. This is why we got all
our cheap but good sensors like accelerometers. A similar thing happened with radar. Not with
Smartphones, but with cars. Newer cars need sensors to measure distance. First came parking
sensors, then the distance sensor with ranges up to a few hundred meters. They operate at
77GHz. So, companies started to develop cheap chips for such frequencies. The quality of such
sensors has to be extremely high compared with our simple CDM324. They need stable frequencies
and sensitive receivers. A similar technology can be used to produce chips for 24 and 60GHz
radar chips. So also those became cheaper.
Here is a selection of more than 20 boards. The
price range starts below $5 and surpasses $100. So what do we get for our money?
Let’s start with the cheapest: They are all below $10, and they all come
from the same company, Hi-Link, operate in the 24GHz ISM band, and contain chips from the
same company. Their output power is quite low, around 12dBm (16mW). This is not unexpected,
as the cost of power increases with frequency.
The biggest difference is the antennas. Some
have simple antennas with a 60-degree opening. Others have up to 4 antennas with a reduced
opening of 25 degrees in the vertical and 45 degrees in the horizontal direction. We
should assume that everything else equal, their range should be much longer. But according
to the datasheet, it is not so. So we have to test them. The LD2450 has another antenna
configuration. Its range should be in-between.
The model numbers containing 11XX
and below seem to be obsolete.
The only other sub $10 board comes from MicRadar.
Its output power is only 6dBm even if it has the same chip as the LD2411. Its antenna is
half the size of the larger Hi-Link sensors, and its datasheet range is 4-8m.
The LD2410B and the LD2411S have Bluetooth. The LD2450, too, but it can
only be used to update its firmware.
So let’s quickly test these sensors. It is
beautiful outside, and Dishka monitors the tests. The LD2410B gets to a range of around 4
meters, not the 6m of the datasheet. You get an app for IOS and Android, and you can easily
integrate both of them into Home Assistant. Either via Bluetooth or connected to an
ESP8266 running ESPhome. The LD2450 only can be connected to an ESPhome device.
The LD2411 and the LD2450 can detect moving targets up to about 6m. All of
them can also indicate the direction of the target. This might be a useful feature
if you want to block a particular area.
The next two sensors are $20, respectively $32.
The IFL2411A is similar to the CDM324 as it outputs an analog Doppler voltage or frequency.
It seems to lack a stable frequency because I did not find a crystal. For me a special module
without a lot of documentation. This 24GHz module from Seeeds has similar specs to the LD2450,
just a much higher price. It seems it has been replaced by one of the newer 60GHz sensors. The
last in the 24GHz crowd is the MR24BSD1. Compared with all other boards, it has a huge antenna. Its
main purpose is sleeping detection. Its range is below 3m, which is ok for its purpose. I will
not include it in the current test because of its special purpose. Maybe I will once make a
video about sleep analyzing radars that would also contain the next contender: the MR60BHA1. It
operates in the next higher ISM band: 60GHz. Its price is $45 plus shipping. Its detection range
is only 1.5m, which is okay for its purpose.
What do you miss if you look at this sensor?
Yes, you are right: There are no antennas. Strange. Only a sharp look at the chip reveals
the secret: The antennas are inside the chip. The 60GHz wavelength is only 5mm. Incredible! But
of course, the detection resolution of such short wavelength signals is extremely good. This
is the domain of our most expensive module: The XM125 from the Swedish company Acconeer. It
works on 60GHz, and has on-the-chip antennas, too. But its main purpose is the detection of
very small and fast movements over a reasonable distance. So, its purpose is comparable with the
other contenders. According to its datasheet, the range is 20m, its update speed is so fast
that it has to be connected via the SPI bus, and its accuracy is millimeters.
The evaluation kit costs around $130. But astonishingly, the sensor alone is only $25. That
is a very good price if the datasheet is right.
I tried hard to get this sensor to show me its
capabilities. Unfortunately, all the examples of their tool show a ton of things, but not what I
expected. The only working example was presence detection at a distance of up to 5m. Nothing
to write home about. I tried walking, I tried it with my (metal) bike, and I tried to measure
speed. Nothing worked. I felt like a real noob. Unfortunately, this is not the first time I have
encountered such code. Particularly, technically savvy people want to show how good they are and
forget that all others are not as good. So guys, create a noobs mode that just shows presence
for the promised 20m range and speed in the same range. Then, you can continue with the res t.
Just to show you how easy it can be: Here is the test of Mathieu’s
sensor. It does what is expected.
60GHz is a fascinating technology. I am working
on another video that uses this ISM band. Today, I can just reveal a detail about why the
60GHz band became a free-to-use ISM band: The attenuation curve of oxygen has its maximum
right at 60GHz. So signals are attenuated a lot which is not good for wireless communication
because you lose much of your precious power. In the next video, we will see if we still get
something usable from this ISM band. Stay tuned.
My verdict? For presence detection, I would go
with the cheap LD2410, and if you need more range, with the LD2411 or LD2450. Also they can easily
be integrated into Home Assistant. As said, the breathing detector boards are for a
different purpose and deserve special treatment.
The XM125 has a lot of potential. And for its
price, it could have been a winner if the creator of this video would have been up to his task.
But keep in mind: These are active sensors and therefore consume around 100mA. So they
have to be powered by mains, not batteries.
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
