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Help needed for building a Vehicle speed detector using HB100 RADAR SENSOR

Pavi98

New Member
Hello all,

I'm trying to build a vehicle speed detector using HB100 radar sensor with Arduino as my school project. I found some posts on Hb100 on the Internet and tried one of them but the output on the serial monitor shows continuous values which are not correct. Does anyone have experience with this HB100 radar sensor? I'll upload the amplifier circuit I used below.

Thank you. IMG_20210430_130732.jpg
 

audioguru

Well-Known Member
Most Helpful Member
If your 1m resistors are actually 1M, then the total gain of the two opamps is 12,317 times and the output will be full of random noise since LM324 or LM358 opamps are very noisy. Use low noise dual audio opamps instead.


Also, with such a high gain the wiring must be compact and shielded so that the electrical 50Hz or 60Hz is not picked up and amplified.
 

Pavi98

New Member
If your 1m resistors are actually 1M, then the total gain of the two opamps is 12,317 times and the output will be full of random noise since LM324 or LM358 opamps are very noisy. Use low noise dual audio opamps instead.


Also, with such a high gain the wiring must be compact and shielded so that the electrical 50Hz or 60Hz is not picked up and amplified.
What will be the most suitable signal amplifier for this purpose? Can I use the following circuit? IMG_20210501_110406.jpg
 

rjenkinsgb

Well-Known Member
Most Helpful Member
This is a repeat of your previous thread:

A doppler radar module in effect gives a frequency out proportional to the speed of movement of any object that reflects a signal.

The "preamp" circuit you originally link to appears to be a limiter to try and convert the low level AC to logic levels.

Have you built and tried that circuit?

(The noise level etc is irrelevant if it is supposed to be a limiting amplifier; it should have extreme gain).
 

Pavi98

New Member
This is a repeat of your previous thread:

A doppler radar module in effect gives a frequency out proportional to the speed of movement of any object that reflects a signal.

The "preamp" circuit you originally link to appears to be a limiter to try and convert the low level AC to logic levels.

Have you built and tried that circuit?

(The noise level etc is irrelevant if it is supposed to be a limiting amplifier; it should have extreme gain).
I tried the following amplifier circuit but the serial monitor shows false values continuously (5.2kmph and 5.1kmph repeatedly even I wave my hand or metal sheet towards the sensor).Also, when I remove the output from the amplifier from the Arduino, I stops showing values on serial monitor. I don't have an oscilloscope to see whether the amplifier working properly or not. The output of the amplifier circuit gives around 2.4V but I'm not sure whether the circuit is working properly. Do I need to change the amplifier and what will be the best solution for this?

Thank you. IMG_20210430_130732.jpg
 

audioguru

Well-Known Member
Most Helpful Member
The LM386 is a power amplifier, not an opamp.
The false output values are probably the noisy opamps amplifying their own noise or unshielded interference 12,317 times.
 

Pavi98

New Member
The LM386 is a power amplifier, not an opamp.
The false output values are probably the noisy opamps amplifying their own noise or unshielded interference 12,317 times.
Can you recommend me a suitable signal amplifier for this case?
 

audioguru

Well-Known Member
Most Helpful Member
I do not know why you need such a high amount of gain.
The LM324 quad opamp you selected is one of the oldest and noisiest one ever made. It was designed to use a very low amount of supply current which causes its noise, crossover distortion and poor high frequency response. With your LM324 and very high gain, your preamp's output will be clipping squarewaves of noise and maybe 50Hz or 60Hz from electricity interference in the air.

I have used a few low noise audio opamps but with a much higher supply voltage that you have. An OPA2134 dual opamp or OPA4134 quad opamp has a minimum supply of 6V.

Of course your preamp has an average DC output of 2.4V because it is biased at half of the 5V supply and the 1M feedback resistor has the input bias current of the LM324 in it.
 

gophert

Well-Known Member
Most Helpful Member
High gain is needed because the radar IF output is in the single-digit microvolts. So gain of a million would be great. Also, the signal is about 50Hz for walking speed (5kmh) doeppler effect and higher as relative velocity (target vs radar) increases.

the size of the target x distance x reflectivity (emissivity) all contribute to the strength of the received echo and the proportional voltage to the IF output. The datasheet says about an -83db (loss) from chirp to received echo.

So high gain, low noise, amp that can handle frequencies up to 10kHz (200kmh) at required gain. There is some DC drift so AC coupling is preferred. The circuit above is from the datasheet (post 1).

these radars are very finicky and internal circuitry is noisier than the LM324 they recommend. Constant false triggers or strange values detected for no reason. It's a toy that works occasionally - even with low noise amps NE5532 with a stable 12VDC supply (5v on the radar).
 
Last edited:

Pavi98

New Member
High gain is needed because the radar IF output is in the single-digit microvolts. So gain of a million would be great. Also, the signal is about 50Hz for walking speed (5kmh) doeppler effect and higher as relative velocity (target vs radar) increases.

the size of the target x distance x reflectivity (emissivity) all contribute to the strength of the received echo and the proportional voltage to the IF output. The datasheet says about an -83db (loss) from chirp to received echo.

So high gain, low noise, amp that can handle frequencies up to 10kHz (200kmh) at required gain. There is some DC drift so AC coupling is preferred. The circuit above is from the datasheet (post 1).

these radars are very finicky and internal circuitry is noisier than the LM324 they recommend. Constant false triggers or strange values detected for no reason. It's a toy that works occasionally - even with low noise amps NE5532 with a stable 12VDC supply (5v on the radar).
Thank you very much for the reply. What do you recommend me to do in this project? I'm actually quite not sure whether this sensor work in this case. Is there a way to make a speed detector using another sensor?
 

gophert

Well-Known Member
Most Helpful Member
If it is for a school project, indoor, short range (5-10 meters to target), stick with this one and find a better op amp. It will not be good for anything you must rely on like a security system, industrial controls or anything else.
 

audioguru

Well-Known Member
Most Helpful Member
The MC33078 dual opamp is low noise and has low distortion. The circuit's gain is 1019. The minimum supply for an MC33078 is +/-5V in text or 8V total where it barely works on its datasheet. The circuit posted has the MC33078 opamps without a power supply that might be a single 5V which is wrong.

The LM324 quad opamp is noisy and has crossover distortion. Its gain is 12317.
 

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