Status
Not open for further replies.

#### alitex

Joined Mar 5, 2007
139
This circuit is a Digital Radar Speedometer. It allows us to evaluate the speed of any object moving, especially cars and other vehicles. The speed is calculated in kilometers per hour (KPH). Its display has three digits. This radar works with the laser reflexion. It sends laser radiation to the object and this object reflects the laser radiation to the radar. To evaluate the speed of a vehicle, we must be in front of it. In other words, the vehicle must come in our direction. The front of the radar must point the front of the vehicle. The radar has the shape of a pistol. In this radar, it has a laser LED and a laser diode. Both have a lens.

The laser LED can send a spot of light to a distance of 90 m (295 ft). It's very important that the distance range of the laser LED is 90 m, if not, the speed will not be calculated properly. The laser diode, which receives the light signal by the laser LED, must be able to detect the light which is same color as that emitted by the laser LED. The laser diode and the laser LED must be placed one beside the other. They are protected by a tinted pane. They must be placed at the front of the radar and point the outside. The radar is powered by a 9V battery and it has a SPST switch to control its power state.

The display, or the speed indicator, is placed at the rear of the radar, just on the right of the overload LED indicator. All the logic components of the circuit must be of the 74AS series and TTL type. Because they have short time of response (less than 1.7 ns) and have high frequency supports (more than 200 MHz). The radar can evaluate the speed of an object moving between 0 to 999 km/h. After this speed, the overload LED indicator will turn on and the "999" will still displayed. The radar displays the speed during 3 seconds, after this time, it displays "zero" (0).

#### Papabravo

Joined Feb 24, 2006
16,793
I have my doubts that this device will work reliably, but it's really hard to see what circuitry you have. It mostly looks like some counters, gates, 7 segment displays, and display drivers. I don't see anything that does arithmetic to compute velocity such as measuring the difference in return time if the device can even do that. Did you design this circuit, or did you find it somewhere? Is there a question in there?

#### alitex

Joined Mar 5, 2007
139

#### hgmjr

Joined Jan 28, 2005
9,029

hgmjr

#### alitex

Joined Mar 5, 2007
139
no it's only post

#### Papabravo

Joined Feb 24, 2006
16,793
I followed the link and found a page full of advertising and hyperlinks to posts and projects. Since there was so much stuff on the page to wade through I decided to give up and ask for a more useful link to the subject of your original post.

#### thingmaker3

Joined May 16, 2005
5,084
The site's search function was pretty well buried, but I was lucky enough to stumble across it. I found this:
http://www.electronics-lab.com/projects/test/021/index.html

Clicking on the picture gave me a bigger schematic, and there is contact data for the designer. No addtional information was offered.

#### beenthere

Joined Apr 20, 2004
15,819
The larger schematic helps. This is a marvel of optimism. I love the tqo LS04's that are the oscillator/driver for the laser diode. The 2 pF cap and low value resistor say this is going to jiggle very fast. But enough emisstivity to illuminate an object 90 m away and give a discernable return? Don't think LS04's drive quite that level of current.

The ambition of the return being able to drive the loads of the LS08 and another LS04 is pretty high, too. I love all the pulse shaping following the receiver. Love the 1 and 2 pF caps.

The speed "computation" comes from ANDing the shaped pulses with the other dual LS04 oscillator. The LS08's output counts the string of LS160's.

With no tweaks, it's going to be a matter of luck if this thing can indicate within 25% of actual speed. With the LS04 gate drive to the illuminating laser diode, the 90 m distance seems wildly optomistic.

#### Papabravo

Joined Feb 24, 2006
16,793
Wow, that was a thoughtful analysis way beyond my intuition.

With a bit of care you can create 1-2 pf of capacitance with traces and wires. Never mind using actual components. You'd need a lab full of instruments to debug and troubleshoot this design if it didn't work.

I confess I'm puzzled about the 90 m requirement for correct calculation. Does it mean that the target must be 90 m away or only that there must be a suitable return signal at any distance up to 90 m, and what gives rise to this requirement? How would you test a laser diode/receiver combination for this characteristic.

Back of the envelope calculation
Rich (BB code):
999 km/hr = 16.65 km/min
16.65 km/min = .2775 km/sec
.2775 km/sec = 277.5 m/sec
An object moving at that speed will cover the 90 m distance between you and the object in 324 milliseconds, run you over, and be long gone, by the time the reading goes away three seconds later. Truly amazing what you find on internet. I couldn't even go that fast in the Mazerati I'd like to own.

#### beenthere

Joined Apr 20, 2004
15,819
The 90 m requirement is the most interesting prt of the speculation. If the circuit is indeed only able to give an acurate speed at that distance, how do you arrange to make a measurement at just the right time? Do you have to parallel the laser with a radar gun to see if the distance was correct?

The distance requirement seems nonsensical, as there is no comparison with the outgoing pulse train. A return from 1 cm would seem to be as valid as from 90 m. Sure would like to know how the circuit adapts to frequency drift in the oscillators.

If the LS160's have a hard time counting pulses, perhaps the design could go to 7490's. They always seemed to count any old glitch.

#### Papabravo

Joined Feb 24, 2006
16,793
For reasons that seem altogether obvious I think this design can be relegated to the dustheap of useless internet claptrap. Building one seems like a great deal of work for a vanishingly small payoff and a large headache to debug if it doesn't work.

#### thingmaker3

Joined May 16, 2005
5,084
The 90 m requirement is the most interesting prt of the speculation. If the circuit is indeed only able to give an acurate speed at that distance, how do you arrange to make a measurement at just the right time?
I thought perhaps 90m was the maximum distance. Still, it sound dangerous... less than 3 sec to get out of the way of a 65mph object after clocking it. (If the circuit works.)

#### hingsifu

Joined Jun 6, 2008
3
where we get proper transmitter and reciever

#### hingsifu

Joined Jun 6, 2008
3
is it get the shure output

#### SgtWookie

Joined Jul 17, 2007
22,221
Hingsifu,
It won't work. I'm sure no one actually built one to this design and actually got it working. It's something that someone drew up and never actually built.

They even got the name wrong; it would be a "LADAR" for "LAser Detection And Ranging" - except it's not capable of detecting range. "RADAR" is an acronym for "Radio Detection and Ranging".

#### hingsifu

Joined Jun 6, 2008
3
any where i get any other circuit for this type speedometer

#### kubeek

Joined Sep 20, 2005
5,757

#### SgtWookie

Joined Jul 17, 2007
22,221
biswajitpatra99 wrote this E-mail to me:
This is the message:

Is the circuit of digital radar speedometer working properly??
I guess you didn't see my reply of June 6th, 2008 where I wrote:
It won't work. I'm sure no one actually built one to this design and actually got it working. It's something that someone drew up and never actually built.
And, I'm also pretty sure you didn't bother to read my tagline that basically asks everyone to NOT E-mail me; instead ask questions on the Board. NO, THIS WON'T WORK, the thread on the other forum has been removed, and I want THIS THREAD removed as well so nobody ever E-mails me about it again!

#### Wendy

Joined Mar 24, 2008
22,545
This thread is a classic case of necromancy and hijacking.

I am therefor closing it.

Status
Not open for further replies.