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Digital radar speedometer

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"Maybe the laser is "modulated with a tone" and the doppler shift changes the tone's frequency"
did't get it.....Is it present in the electronics -lab project???

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"Maybe the laser is "modulated with a tone" and the doppler shift changes the tone's frequency"
did't get it.....Is it present in the electronics -lab project???

Yes, the laser beam is modulated in our project. The oscillator is a two-inverter Cmos type without any accurate parts, and without any calibration adjustment.
The oscillator appears to operate at a high RF frequency and a similar but lower frequency oscillator is used for gating the photodiode's signal.
The text doesn't explain how the circuit is supposed to calculate speed.

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Audioguru what it wants to do? referring to the truth table? 
How to calculate it's frequency?u posted the formula on first page but R1 is not present here......R2<<<<R1 here????
Thanx

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You can't calculate the frequency because its timing capacitor's value is much less than stray capacitance of the wiring. 2pF and 10pF are nearly nothing!

I don't know how the circuit is supposed to calculate speed.

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"An RF mixer circuit "(detector diode)" gives their sum and their difference as a beat tone."
I think by detecter diode u mean to refering to the schematic .....r u talking about the photodiode? The received signal will have the transmitted frequency+ doppler shift and I think there difference has to be takem to get the audio frequency?

ramsey says that for each mile per hr the target is travelling towards radar gun the doppler shift will be 7.76 .......Is it for ladar also?

Any idea what these blocks r doing (Plz forgive me !I m really new to this but I want to learn(as much as possible))

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I went through a link in google....and it says that for 2.6GHz transmitted frequency the doppler shift for eachmi/hr is 7.74..........
How to calculate the transmitted frequency in this case of ladar?
So,I think that was what I was trying to claculate ...... But the formula can't do it.......Can't a laser beam transmitted with a known frequency??


(
-      Doppler Lidar
-    Measures the velocity of a target
-    Light transmitted from lidar hits target moving towards or away from the lidar, wavelength of light reflected/scattered off the target will be changed slightly- Doppler shift
-    If target moving away from lidar, return light will have longer wavelength (red shift), or shorter wavelength if moving towards lidar (blue shift)
)
(Radiation used by laser radars is at wavelengths 10,000 to 100,000 times shorter than that used by conventional radar
)

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The logic circuits you highlighted are monostable multivibrators that make a pulse of a certain polarity (each circuit has the opposite output polarity of the other) when they are triggered by a short input signal. One pulse resets the counter and the other pulse enables the counter to count for the duration of its pulse. These pulse generators are not accurate and are not adjustable in this circuit.

The colors of light are its frequency and it is extremely high. Electronic circuits can "see" different colors through colored filters to determine the frequency of light. This circuit doesn't use colored filters so I don't know how it detects the doppler shift of the laser beam, maybe it detects the frequency shift of the beam's RF modulation.

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:o oh! I thought u were referencing photo diode....the mixer not present in our circuit(laser)???? How can that RF modulated frequency be determined in the ladar?
By now what I've learnt is that the rf frequency should be known.....I can't see without that how one can proceed ...... RF modulated...Frequency Modulated ..I think?

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Our Laser Speedometer project has two oscillators:
1) A high radio frequency oscillator that pulses the laser at maybe 100MHz.
2) A medium radio frequency oscillator that gates the received pulses that might be doppler shifted in rate. The pulses are gated into the counter for a time period determined by the lower frequency oscillator. 

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The signal entering in the ramsey display schematic(low pass filter) is the doppler shift? which is, for 2.6 GHz case, 7.76Hz for each mi/hr.....So,the crkt may be designed for 7.6Hz.....
Can we FM modulate the laser beam?how? at 2.6GHz?

If we fm modulate it and after the signal is received ......we pass both the signals(transmitted and reflected) in a mixer and gets their difference, the doppler shift and if we have 2.6GHz transmitted signal ,then we only have to connect the transmitter and receiver+mixer part to the ramsey

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The signal entering in the ramsey display schematic(low pass filter) is the doppler shift? which is, for 2.6 GHz case, 7.76Hz for each mi/hr.....So,the crkt may be designed for 7.6Hz.....

No. Then its max speed detection is a snail's pace. Its filter cuts noise above about 760Hz (for 100mph) or a little higher.

Can we FM modulate the laser beam?how? at 2.6GHz?

Cell phones FM modulate 2.6GHz but FM and 2.6GHz are useless in a laser speedometer.


I haven't got into it that how it displays speed.....
I can't get what the 2nd oscillator do in the electronics-lab pro....what do u mean by gating?

The 2nd oscillator in our project is at a lower frequency than the pulsing modulation oscillator and drives a logic gate in the counter circuit. A logic gate has an input for pulses and another input to allow or not allow it to pass the pulses. Then the counter counts and displays how many pulses passed in the time allowed by the 2nd oscillator's time period. If an object is moving toward the receiver then maybe the doppler shift causes the received pulses of light to be at a higher rate than the transmitted rate.

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What's the purpose of this(see labeled block)?
I m unable to find a good detail on ladars in google......Have u any? there are many about radars but none explaining the steps of ladar.....
You say that there is no mixer in our ladar......then It is not using the doppler shift????? Since the mixer will give us the doppler shift......
Are ladars absolutely different from radars?
Still I don't get how to determine the transmitted frequency in ladars.......
This seems to me giving no results :'(

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I've never seen a radar or laser speedometer circuit before. I am not sure what the Photodiode Circuit does, maybe a very short pulse generator.
The same author has about the same circuit using the same ICs in another project of his and he doesn't describe it either: http://www.electronics-lab.com/projects/pc/023/index.html

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Yeah, Audioguru,it is hard to understand without the details of the project.....I don't know where to find about it.....Googling didn't help me......


You say that there is no mixer in our ladar......then It is not using the doppler shift????? Since the mixer will give us the doppler shift......

Sorry!any idea about this :-[

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Our laser speedometer circuit doesn't have a mixer because light frequency is too high for an electronic mixer circuit. Radar uses radio waves and has an electronic mixer diode.
Our laser speedometer circuit counts the frequency of the modulation of the reflected laser beam. I assume that the doppler frequency shift also occurs to the modulation frequency.

The RING pin on the jack is from the output of the mixer and it is going to the input of the lowpass filter in the amplifier circuit.

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Our laser speedometer circuit counts the frequency of the modulation of the reflected laser beam. I assume that the doppler frequency shift also occurs to the modulation frequency.


yeah,Acc to my knowledge,doppler shift occurs to the modulation frequency......But how is it useful......Just leave the crkt at electronics-lab and tell me that how he counting of the received signal with doppler shift can be useful?How can it be converted to speed?Just ideas not referencing the ladar crkt if it is wrong.....

yes,that's what I was saying about the ring pin:-

The signal entering in the ramsey display schematic(low pass filter) is the doppler shift? which is, for 2.6 GHz case, 7.76Hz for each mi/hr.....So,the crkt may be designed for 7.76Hz(or it's multiples to masure the speed like this 7.76*10=77.6 which means 10 Miles/hr)?????.....


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