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# Digital radar speedometer

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How do radar guns work?

Radar guns utilize the "Doppler principle" to determine speed.
They transmit radio waves at microwave frequencies, and when these waves strike a moving object, they are reflected back to the radar gun at a slightly different frequency. The gun then "mixes" the reflected signal with the transmitted signal, and ends up with a frequency that represents the difference between the two. Since the difference in frequency is generally a number of hertz or kilohertz, it is in the audible range, hence the term "Doppler tone". The speed of the moving object can be derived by performing a calculation using the frequency of this Doppler tone and the original transmit frequency.

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How do laser guns work?

"Laser guns do not use the Doppler principle" like radar guns do. Instead, they use "time difference of arrival". The laser gun sends out a pulse, and calculates the "time of flight" for the pulse to be reflected back to the laser gun. Since the speed of light is a known value, the distance between the laser gun and it's target can be calculated by the time of flight. The laser gun takes multiple distance measurements, and by comparing the different distance measurements over time, it can determine the speed of the target.

What are FMCW and AMCW trying to do here
http://www.swedetrack.com/obstact.htm#4
?

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Our Laser Speedometer project doesn't have an accurate quartz crystal nor a calibration pot so I guess it works by majic!

i think it not work by magic. Ok, this radar works with the doppler effect. It converts variation of frequency into frequency and it measures this frequency to display the speed. The variation of the frequency of the modulation is created by the impact of vehicle against the wave. More the speed of the vehicle is high, more the variation of the frequency will be high. At the speed of the light, the rythm of variation of frequency is the same as the modulated frequency. You can determine the output frequency if you know the modulated frequency value and speed of the car.

the 74as series can be replaced with the 74hc but from what i know the 74hc is a CMOS type, is there 74hc in TTL type?

i want to ask something? what is the major different between TTL and CMOS IC, the different that we can see from the IC... exactly like it shape or marking?

I hope you can help me... :)
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the 74as series can be replaced with the 74hc but from what i know the 74hc is a CMOS type, is there 74hc in TTL type?

i want to ask something? what is the major different between TTL and CMOS IC, the different that we can see from the IC... exactly like it shape or marking?

I hope you can help me...

???

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the 74as series can be replaced with the 74hc but from what i know the 74hc is a CMOS type, is there 74hc in TTL type?

i want to ask something? what is the major different between TTL and CMOS IC, the different that we can see from the IC... exactly like it shape or marking?

The AS and HC ICs are in the same case.
The AS is much faster and operates at a much higher frequency than the HC.
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i think it not work by magic. Ok, this radar works with the doppler effect. It converts variation of frequency into frequency and it measures this frequency to display the speed. The variation of the frequency of the modulation is created by the impact of vehicle against the wave. More the speed of the vehicle is high, more the variation of the frequency will be high. At the speed of the light, the rythm of variation of frequency is the same as the modulated frequency. You can determine the output frequency if you know the modulated frequency value and speed of the car.

I think for that u must know the transmitted frequency ......Can it be known here?
how's the variation of the frequency taken and passed to display speed(in which part of the crkt, as mixer is used for rf crkts) ?.....

U said 74hc can be used here.....I again read the desciption of the crkt and it says ttl type shoulb be used.....74hc is cmos type??
Thanx
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The AS and HC ICs are in the same case.
The AS is much faster and operates at a much higher frequency than the HC.
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Laser radar block diagram and explaination:-

http://profusion.ittc.ku.edu/publications/documents/Allen2002_RSL%20TR%2018680-2.pdf

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That is another way to do it. Who is going to design a circuit that works that way?

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The AS and HC ICs are in the same case.
The AS is much faster and operates at a much higher frequency than the HC.

74AS can be replaced by 74HC because i already asked the author of the crkt....
he say that the 74AS is a fast and high frequency ic but 74HC is higher to...
there was only a little bit different in they frequency respons..
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I think for that u must know the transmitted frequency ......Can it be known here?
how's the variation of the frequency taken and passed to display speed(in which part of the crkt, as mixer is used for rf crkts) ?.....

?

That is another way to do it. Who is going to design a circuit that works that way?

I will design it :)...but for that we have to wait for atleast 1-2 yrs. :) since this subject is not included in my course this year......I am unable to understand themethod upon which e-lab project is based....Can u tell me which method of the two looks good....And please don't get angry with me....I can't leave that work which seems to be hard or impossible....I always try to make it possible ....It's my habit.

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