Digital radar speedometer

[audioguru2]

I read that laser speedometers are better than radar.......About that particular circuit what's your opinion.....?

Our "Digital Radar Speedometer" project is titled wrong. It doesn't use radar, it uses a laser.
I don't think it works because its photodiode is backwards and doesn't have an amplifier.

The radar circuits might work. Try them.

 

[MNA]

Have a look on this site(about ramsey radar):-
http://www.rcgroups.com/forums/showthread.php?t=205460&page=2&pp=15

Audioguru,what is microstripline?

View attachment 39073

 

[oldgrandpainmi]

2 quick things-

A great source of d-Flip flops-  DigiKey.  Order their free catalog on cd or paperback (almost 2"thick).  They also have most or all of your laser diode needs.

Also, I use ScreenHunter to screen capture.  It is free, saves everything as a .bmp file (which you can save as something else) and works great!

oldgrandpainmi

 

[audioguru2]

Audioguru,what is microstripline?

A micro-stripline is a way of wiring microwave RF parts so that the plumbing forms tuned circuits and impedance matching devices. I have never played with frequencies as high as microwaves so I don't know anything about it.
A search in Google might find a description about how it works.

 

[MNA]

Have a look on this site(about ramsey radar):-
http://www.rcgroups.com/forums/showthread.php?t=205460&page=2&pp=15

 

[audioguru2]

The Ramsey radar gun kit is only good enough for a kid's science fair demo?

 

[MNA]

The Ramsey radar gun kit is only good enough for a kid's science fair demo?

I know that these crkts can't match with the costly made.......
But why....

2View attachment 39074

 

[MNA]

7  what's the function of LM324(amplification or comparator or else) and 4093 here ?

 

[audioguru2]

I know that these crkts can't match with the costly made.......
But why....?

They are cheap and crude. A free-running oscillator is used in the display circuit and its frequency is adjusted for calibration. A real speedometer uses a very accurate quartz cryatal oscillator.

2

 

[MNA]

(free running oscillator in the display circuit) Can u point me where?
the laser diode is receiving only the reflected frequency???? Doesn't it get mix with the transmitted frequency in air?
If we have two inputs with different frequncies,is there any way that we get their difference????
how can we divide by 7.76 Hz using logic ics?
Why LM324 is used?I mean what is it doing?
Thanx

 

[audioguru2]

(free running oscillator in the display circuit) Can u point me where?

It is a Cmos Schmitt-trigger oscillator whose frequency changes with supply voltage changes and temperature changes. See my attachment.

the laser diode is receiving only the reflected frequency???? Doesn't it get mix with the transmitted frequency in air?

The laser doesn't shine on the photodiode. Maybe the laser is modulated with a tone and the doppler shift changes the tone's frequency, then the two tones are mixed in the receiver.

If we have two inputs with different frequncies,is there any way that we get their difference????

An RF mixer circuit (detector diode) gives their sum and their difference as a beat tone.

how can we divide by 7.76 Hz using logic ics?

A logic divider divides a frequency by a whole number.

Why LM324 is used?I mean what is it doing?

The beat tone is weak so is amplified. The weak beat tone has noise so is filtered. See my attachment.

 

[MNA]

"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???

 

[audioguru2]

"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.

 

[MNA]

there r two oscillators (two inverter c-mos type) Isn't it? Any idea what's the second one doing?

View attachment 39077

 

[audioguru2]

The 2nd oscillator gates the clock pulses to the counter from the photodiode.

 

[MNA]

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

 

[audioguru2]

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.

 

[MNA]

"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))

View attachment 39082

 

[MNA]

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
)

 

[audioguru2]

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.