HB100 Radar speed detector

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RogerClark
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HB100 Radar speed detector

Post by RogerClark » Wed Aug 23, 2017 11:26 pm

I had time last night to power up one of those HB100 Doppler radar modules.

You just need to supply 5V, and it outputs the "IF" signal, which is be mix product from the transmitter and the incoming received signal.
This is the sum and the difference of the Tx and Rx, but the only usable signal is of course the difference, which is in the audible range, as the sum is 20GHz !

Anyway, looking on the IF output of both the modules I have, it does output a signal, but its very weak and there seems to be a lot of noise.

I did try feeding the IF signal into the input of an audio amplifier but it just seemed to amplify the noise, far more than the signal.

I'm not sure where the noise is coming from, as I'm using a linear PSU, but I will need to try adding some decoupling caps directly to the module

I found this circuit for amplifying the signal from these devices

Image

And it looks like I can't simply use an audio amplifier module for this, as the first opamp stage has a gain of 100 and the second opamp stage seems to be setup to maximum gain, which is probably to create square waves into the Arduino input.

The 2 x 100k resistors and cap in the top left of the circuit, seem to form a voltage divider to produce 2.5V, and I think that voltage is fed into both of the opamps, as a central reference reference voltage.

But I think that possibly that circuit is designed to convert the IF frequency into a voltage as the last opamp is probably configured as an integrator

I found these 2 product data sheets for the HB100

https://www.openimpulse.com/blog/wp-con ... asheet.pdf

https://www.openimpulse.com/blog/wp-con ... n_Note.pdf

Interestingly the same circuit which is shown as the Arduino interface on www.theorycircuit.com seems to be in the Application Note.
So I'm not convinced whether its the ideal circuit for generating square waves from the output of the module.

I know other people have used this module for doppler speed measurements, so I will need to find the amplifier circuits

Edit.

Direct link to one of those PDF's

http://www.apollounion.com/eweb/download/410.pdf

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Pito
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Re: HB100 Radar speed detector

Post by Pito » Thu Aug 24, 2017 6:51 am

The second opamp is an amplifier too, with gain about 120, the 2.2nF creates a low pass filter in both (corner freq is aprox 74Hz -6dB). The 4.7uF and 10k creates high pass corner aprox 3.5Hz. So in total the gain is aprox 100 x 120 = 12000 (inside a bandpass 3-75Hz).

With none signal at the input (disconnect the module but leave the first 12k there) you have to see DC 2.5V (plus minus opamp's input noise multiplied by amplifier gain, maybe ~hundred(s) of mVpp) at the output of the second opamp. The center (DC) of your signal will always be at 2.5V.

Anything with amplitude bigger than 200uV (inside the band pass freq) will saturate the amplifier (you will get a "square" wave 5V out, or 0.5-2V less) - it depends on the opamp types (ie. rail2rail).

PS: the docs indicates the movement beats around 100-150Hz, so I would decrease the 2.2nF caps to say 1nF in order to get the beat freq inside the bandpass..
Last edited by Pito on Thu Aug 24, 2017 7:37 am, edited 1 time in total.
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Re: HB100 Radar speed detector

Post by RogerClark » Thu Aug 24, 2017 7:36 am

@pito

Thanks

I don't have any descrete opamps , but I found this http://www.instructables.com/id/Radar-W ... nd-MAX446/ which shows how to convert a MAX446 based microphone sound detector as the amplifier

Its probably not as good as the 2 opamp circuit, but I will try it, as it will be easy to wire up.

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Re: HB100 Radar speed detector

Post by Pito » Thu Aug 24, 2017 7:42 am

With that MAX module you have to remove the R2 resistor when connected to the radar output (leave the 12k at the module's output there).
With R5=1k you get gain=100, with R5=100ohm you get gain=1000, etc.
Also I would increase the C2 to something like 1uF (ceramic/foil) to move down the input's highpass freq..
Of course 12000 amplification with a single opamp is usually not to recommend :), but you may try..
Last edited by Pito on Thu Aug 24, 2017 7:50 am, edited 1 time in total.
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Re: HB100 Radar speed detector

Post by RogerClark » Thu Aug 24, 2017 7:47 am

@pito

Yes. I know I need to change the feedback resistor.

I think in that post, the author change the 100k to 1M, so increased the gain by 10 x

I could remove it completely, but I think it would end up being worse as I already have problems with noise

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Re: HB100 Radar speed detector

Post by Pito » Thu Aug 24, 2017 7:53 am

Best you would use 2 modules in series (each with 1Meg feedback). Mind the coupling capacitors (C2) should be bigger. Also remove the R2.
C4=100pF - with that capacitor and 1Meg the upper corner freq will be maybe 2kHz, thus you will get a lot of noise. Your beat signals are up to say 200Hz, so I would increase the C4 to 1nF.
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Re: HB100 Radar speed detector

Post by RogerClark » Thu Aug 24, 2017 8:01 am

umm

I just looked at the sound detector modules that I have and they are different :-(

They use a LM393.

I'll need to see if I can find a schematic for that type, so see if its practical to modify them


Edit. I just looked at the datasheet and the LM393 is a comparitor not an opamp.

PS.
I did try using a class D audio amp module PAM8403 but I had issues with noise :-(

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Pito
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Re: HB100 Radar speed detector

Post by Pito » Thu Aug 24, 2017 8:22 am

Roger, I would guess you will not be happy with your measurements unless you wire the amplifier as on the schematics above.
The useful (your beat) output signal from the module is in range of uV, and only up to couple of hundreds Hertz of frequency. You have to consider that.
Doppler shift output from IF terminal when movement is detected. The magnitude of
the Doppler Shift is proportional to reflection of transmitted energy and is in the range of microvolts (μV). A high gain low frequency amplifier is usually connected to the IF terminal in order to amplify the Doppler shift to a processable level (see Annex 1). Frequency of Doppler shift is proportional to velocity of motion. Typical human walking generates Doppler shift below 100 Hz. Doppler frequency can be calculated by Doppler equation in Annex 4.
The Received Signal Strength (RSS) is the voltage measured of the Doppler shift at the IF output. The RSS figure specified in the technical data sheet is level of a 25 Hz Doppler shift, generate from the modulated microwave signal received at the received antenna, The received microwave signal is attenuated to 93 dB below the transmit microwave signal from the transmit antenna of the same unit. The 93dB loss is the total losses combining two ways free space loss (82.4 dB for 30 meters at 10.525 GHz), reflection less and absorption loss of the target, as well as other losses.
This RSS figure can be view as an approximation of the output signal strength for a human at 15 meters away walking straight to the module at 1.28 km/hour.
The ready to use audio amps are usually 100Hz-20KHz, working with hundreds of mV inputs (low gain). Your signal will be totally lost in the noise (and most probably it will not fit into the amplifier's bandwidth).
The above schematics with maybe a better opamps (ie. modern low noise) would be definitely my starting point..
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Re: HB100 Radar speed detector

Post by RogerClark » Thu Aug 24, 2017 10:32 am

Thanks Pito

My local electronics shop should have the LM324 in stock, so I will drive there at the weekend and buy one (albeit at an inflated price of $2.50 !)

I'll also take a look in my box of IC's but I think its mainly old 74xx series

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Re: HB100 Radar speed detector

Post by Pito » Thu Aug 24, 2017 11:54 am

$2.50
It seems there is only one guy (DaveJ) except you messing with electronics on your continent :)
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