# Distance Measurement With Radio Waves

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Introduction:
First of all, we want to excuse us for our bad English. (German pupils :D)
We invented a new, inexpensive device to measure distances up to 1.5km (about 1 mile) with accuracy about ±5 Meter (15 feet). The use of radio waves makes it possible to measure without the target being in sight. This means, you can measure distances through whole buildings.There are many rangefinders available, which are working with sound waves or lasers. A disadvantage of distance measurement with laser rangefinder is that you must center up the beam to the receiver and ensure that there are no obstacles along the laser beam.
Schematics and layouts are 100% own work, no copy and paste, only the transmitter and receiver modules had been bought.We already took part with this project in a German youth science competition called „Jugend-Forscht“ and won the 1st prize.

## Step 1: Step 1: Basic Idea

Step 1: Basic idea
To put it simply, the main part is an exact stopwatch, which measures time with a resolution in nanoseconds. It is used to stop the time the emitted radio wave is travelling. Because the spreading rate of radio waves is identical with velocity of light, you can calculate the distance between the two devices (measuring points) by a given travel time of the radio waves.The stopwatch contains a crystal with a clock rate of 30 Megahertz and a couple of decade counters (High- Speed CMOS). To display the stopped time, binary outputs of the decade counters must be converted to be easier readable on 7-segment-displays. The process of a single measurement:
1) The measurement is being initiated (started with a button) by the user at the basic station (1st point)
2) Counter starts, at exactly the same time a 434 MHz AM transmitter module emits out a 1st radio wave
3) The radio wave gets into the receiver at the 2nd point, and immediately starts the 2nd transmitter at a frequency of 868 MHz
4) The 868 MHz wave is being received at the basic station and stops the counter
5) The travelling time can be read on the display.

## Step 2: Step 2: Calculation of Distance

Step 2: Calculation of Distance
The formula:
Δs = (Δt * c) / 2

Δs: Distance in m
Δt: Wave travelling time
c: Speed of light (299,792,458 m/s)

For Example, the Display shows ‘17’ (leading zeroes are shown, too.), the radio wave has been 560ns (nanoseconds) on the way.
(5,6*10-7s * 3,0*10^8m/s) / 2 = 85m
Inserting the values in upper formula, you’ll get a distance about 85 meters.

## Step 3: Step 3: Problems/Accuracy

Step 3: Problems/Accuracy
The use of a 30MHz crystal does not allow creating a very precise time base. The aftermath will be an error on the distance about ±5m. Increasing the frequency of the time base will improve the accuracy: The higher frequency, the more precision . Although there are several crystals available on the market with frequencies up to 100MHz (5th harmonic), the actual limit is the maximum clock frequency input of the 74HC4510 counters with 53MHz. Farnell offers counters up to 1200MHz, but they are expensive, only available for companies and come in boxes with hundreds of it. Another problem is that free frequency bands (434 and 868 MHz in Europe) can be used by any other equipment like walkie-talkies. This means the device will not work, because the receivers will get some other signal that is in the air.
The picture shows on the left side the distance measured by out device. The real distance is plotted on the ground. To prevent errors, several measurements had been performed. The fist one is shown by the blue line, the second by the red one an the real distance is located by the orange one.

## Step 4: Step 4: Parts

Step 4: Parts
Semiconductor:
5x 74HC4510
5x 74HC4543
3x 74HC4040
1x 4093
2x 40106
2x 78L05
1x BD175
1x BC556
32x 1N4148
1x LED red small
5x 7-segment-display

Resistor:
All resistors are 1% metal film, unless otherwise specified.
40x 390R
1x 1k
1x 2,2k
1x 8,2k
2x 10k
1x 12k
1x 15k
4x 22k
1x 27k
1x 1M
1x 10M

Capacitor:
2x 2,7pF
1x 470pF
5x 10nF
4x 100nF
1x 0,22µF
2x 470µF
2x 100µF

Misc:
1x 30 MHz crystal
1x Transmitter module 434 MHz
1x Transmitter module 868 MHz
1x Push Button (to start the measurement)
1x Momentary Switch (to reset the clock watch)
1x small switch (to choose between permanent or temporary display)

## Step 5: Step 5: Schematic

Step 5: Schematic
We thought about uploading layouts for making a PCB, but it it’s not worth it, because the pin connections and alignment of transmitter/receiver modules are always different. (We got very exotic ones from a company in Italy, produced in Taiwan :D) If you decide to buy one – with a high probability they wouldn’t fit in our PCB.

## Step 6: Step 6: Trilateration

Step 6: Trilateration
Suppose you built such a unit, you may ask yourself if distance measurement only is a bit boring. Good news: If you built three of these, you can use them for trilateration.

http://en.wikipedia.org/wiki/Trilateration

Because a radiowave spreads spherically, at 3 given distances a point can be clearly defined:
A circle is simply the set of all points (infinite) with the same distance to a point. The intersection of two spheres is a circle. The intersection of three spheres is one point.

This can be used tracking an object for example a car (GPS uses exactly the same principle.)

## Step 7: Step 6: Conclusion

Step 6: Conclusion
This new technique of measuring distances is a great alternative to conventional laser methods. But the largest advantage is that you can measure through whole buildings. And the way it is built up is also simple enough to push this project easily forward with minimal knowledge of electronic. And you can use it without any knowledge of measurement technics.
To sum it up:
It's easy to use, it's easy to built, it's cheap and it's a new revolutionary method of distance measurement

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## 125 Discussions

Hi , how is this different from the radar guns style of measurement?. Obviously radar is a higher frequency than this. Please elaborate. 2) And is there any industrial grade tool for measuring distance and speed like what you have shown, perhaps a production grade radio frequency measurement tool.

i need your email id to contact regarding my project based on lidar

is it possible to biult a reciver with same pint at transmitter so that we can get reflection of radio wave to measure distance

it seems to me that if you guys used walkie talkies conected to a microcontroler instead of building your own custom radios you would be able to have greater accuracy (maybe) and a lower cost

6 replies

we didnt build our own radio, described on step 5, we bought some and i think the costs, about \$75, are very low. another advantage of building it like we did you dont have to programm some microcontroller, in our point of view this way seems to be easier. and the accuracy depends only on our clock signal with 30 MHz, descibed in step 3.

@Jones Electronics: dude can u just mail me a schematic with better quality and visibility to this e-mail address "pendyala87@gamil.com"

If people are looking for cheap radios to try this out, I can recommend the Baofeng UV-3R. It can be run at 1 or 2 watts, is dual band, VHF/UHF and I think 2 of them can be set up to work as a cross band repeater. The nice thing about these is that they are made in china and don't aim to comply with North American band plans, so they transmit on the entire vhf and uhf bands without restriction, which is great for finding and using "white space" where there will be no interferecne. They also have a simple VOX feature which could help with the cross band repeat.

Hi.

"The 868 MHz wave is being received at the basic station and stops the counter"

How is this done? how - technically - can you have the receiver know when exactly the signal was received in a nano second accuracy?

Thanks.

Hi.

Maybe some one knows how can I transmit a fast rising signal (1-3 ns) to a distance of 100 km and watch it on an oscilloscope using the method described here or any other method?

Thanks,

Mike.

This is a cool project. Is it possible to do it using a microcontroller like the PIC or Atmega? And writing the distance calculation algorithm in C?

HI :) I'm a Doing a project by the way that involves with radio and distance measurements, So how can I use Arduino for this? Or Can I even use Raspberry Pi?

6 replies

You can't use Arduino at all for this purpose. 1) you need hi presion osc. crystals those freq deviation will give you +/-180 m of accuracy error 2) Much higher freq, cause 8mhz - will give you 300.000.000m/s /8 000 000Hz = +/-38m of error 3) And arduino it self has problems to count amount of cpu steps.

I am Making Step 6 :) "Trilateration" But I don't want the sender to know the exact location of the receiver, what I want the Arduino to do is to only compute the Formula of the Trilateration with the given Distance by the sender, The sender should send the Distance by radio too :)

I would Like to set 10m distance of each sender (forming a triangle) and I Will be the one holding a receiver in my hand and looking at the Display and know where I am Inside the Triangle!

is my Imagination even possible? Because if It is possible I would Really Make This

Dear sir, I wonder if you may be able to assist with this query I sent to jones electric?, please see below

Hi there jones electric , I have a small project where I need to measure distance changes over about 0-80m

I would be more than happy with a resolution of 1-2 metres.