Introduction: Distance Measurement With Radio Waves

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 Receiver module 434 MHz
1x Receiver 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

Comments

author
Ronit Ve IsraelS (author)2017-02-25

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.

author
Ronit Ve IsraelS (author)2017-02-23

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.

author
alyha (author)2016-12-12

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?

author
GroverR (author)2016-08-14

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?

author

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.

author

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

author

https://fruct.org/publications/abstract16/files/Shc1.pdf

author

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.
Could your system be adapted at all.
I would like the output to go on and modulate the rpm of a brushless DC motor via Arduino or similar.
Kind regards , John

author

Look for "algorithms based on RSSI method" - this is the only way

author

You are dropped From Heaven BRO! :* I love yah!!

author
gvillenap (author)2014-07-30

Sir, my tesis is your project, is there anyway that we can have a small talk? I really appreciate some help with it. I was planing to use a uC arduino due (84 MHz) and 2 tranceivers (NRF24L01, 2.4Ghz) to comunicate them. but I found troubles in there. Please I really need some help. Thanks. Giancarlo

author

I knew this problem! These transmitters don't have a constant delay... somethimes they send the signal out within 1ms somethimes it takes 3ms.

You can only solve this problem by using dirty transmitters. They just have to transmitt a peak. because of that there is no long protocoll, crc or something else, simple but works constantly

author

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.
Could your system be adapted at all.
I would like the output to go on and modulate the rpm of a brushless DC motor via Arduino or similar.
Kind regards , John

author
ohoilett (author)gvillenap2014-10-26

I am actually trying to do this as well. Have you found any success?

author
gvillenap (author)ohoilett2015-03-31

Nope, i didnt. I did another project, but Im still interisted in this one

author
ImranB9 (author)2016-09-03

Hi there. Loved the project. Thanks for sharing Jones! I cannot understand what's happening in the areas marked A, B, C in the diagram attached. Can anyone explain?

ask.png
author
RitendraM (author)2016-06-09

Hi Jones Electronic. I am trying to make this module for a project of mine. The problem is Im unable to find the components listed in the parts list. Additionally, the parts list does not match the components used in the circuit diagram. For instance, 10 74HC4510 ICs are used in the circuit whereas the parts list mentions just 5. 74HC4543 is not used in the circuit. I have not been able to obtain 4510 and BD 175 as they are not available anywhere around where I work or even online. Can you please clarify this issue and suggest alternate ICs and part numbers? My email id is ritendra.mishra@gmail.com. I need to finish this urgently and I would be grateful if you could reply promptly. I eagerly await your reply.

author
JonasSukko (author)2016-01-28

Hi.
This is very good info on how to measure with RF, the best I have found online so far.
I am working on a similar projekt. But i want accuracy in about +-1-3 cm and a maximum range at about 10 m and not about 5 m and 1.5 km as you got with your specs.

Is there an easy way to make it more precise?

author
JohnL373 (author)JonasSukko2016-05-05

That's going to be very difficult. You would need to measure time in picoseconds

d = 1 cm = 0.01 m
v = c = 299 792 458 m/s

t = d/v
t = 3.336e-11 or 33.336 picoseconds to be exact.

So you will need a clock rated in gigahertz

f = 1/t
f = 1/3.336e-11
f = 29,976,019,184 or ~ 30 GHz

While most of today's available ICs operate in the MHz range, finding such high-speed chips will also be difficult and expensive. So, IC's are impractical for this implementation, you would need atomic clocks like the ones used in GPS satellites.

author
kesha9 (author)2016-03-06

is it possible to use it to set say "bubble" in space of certain radius.

like a leash for a dog, so it wouldn't ran away?

Thank you ;)

author
Isaace11 (author)2016-01-04

I must ask.. Is there a way to create alarm system for a child when there are too far away from you? For example, create a project with one transmitter and receiver that will trigger alarm one by one

author
dandyvandy563 (author)Isaace112016-01-08

I would think you could use something like an arduino to incorporate into it? I am looking into doing something similar for seeing how far away my drone is. Also you make a great point about kids because keeping up with them in stores is extremely difficult. Great idea and post. No need to excuse your english for it is far better than many whos native language is english especially here in the USA.

author
Shine6 (author)2015-11-27

awesome idea.

author
sankarmohit (author)2015-09-22

I need clear schematic diagram. Can you give?

author
sankarmohit (author)2015-09-22

I need clear schematic diagram. can you give?

author
ve6cmm (author)2015-08-04

Wow. This project seems to have been going for several years now. One thing that I haven't seen and just came to me is that using radio's at both ends may end up causing some problems do to MULTIPATH. This is common on VHF and UHF frequencies. Buildings and other large objects can reflect these signals and the reflections may actually be stronger than the direct signal (as it may be behind a building). This would be difficult to account for and would obviously take longer to get to the control radio.

I will try and find some time to draw up my idea mentioned earlier.

author
ve6cmm (author)2015-03-26

I am not sure if anyone mentioned it, but you don't seem to have included the time for the measuring transmitter (Interigator) to turn on fully OR the transition time for the far receiver to turn on the far transmitter. Lets call the far Receiver and Transmitter the TRANSPONDER. This can be milliseconds. One of the posters had suggested a means for altitude measurement, which is just radar, and the travel time for the transmitted pulse to hit the target and reflect back to the radar results in the distance (12 microseconds per radar mile). What you are proposing is similar to aircraft IFF Systems.

To get around much of these problems, you could modulated the Interigator signal and then pass the modulation through the Transponder, whose signal you would receive at the start point. The difference in time between the original modulation and the received modulation is the total transit time. The higher the modulation frequency, the more accurate your timing would likely be. You have to consider the time it takes for the modulation signal to pass through all the electronics, but measuring this time would be simple to do on a bench. You could use a simple one IC timer/counter (Intersil made these) to do all the measurment for you. I am sure that you could get a complete stop/start timer from China for a few dollars. I am not sure, but I would suspect that the temperature of the various electronics could affect the transit time enough to limit the accuracy if not taken into account.

A square wave used to modulate the system would probably work well for most applications, and the electronics would be simpler. However, a SINEWAVE would likely give you better accuracy. A stream of 5 or 10 cycles of the modulation waveform every second might make things easier.

If you are trying to get 1ns accuracy, then you would need a counter that would be able to respond to 100 MHz or more.

An exclusive OR gate could be used to compare the transmit and received signals, the pulse output from the gate would be the total time of the modulation hitting the first transmitter, and arriving back at the starting point. If the transmitters and receivers were always on, then only the time it takes for the signal to pass through all of the electronics (a constant) would have to be subtracted from the total time.

The closer you are to the transponder, the higher the modulating frequency would need to be. The further away the transponder is, the lower the modulating frequency would need to be. The nice thing about this is that the transit time through the electronics would stay the same. The timing/counter electronics would stay the same. Only the modulating frequency would need to change, depending on the expected distance. When you don't know how far away the Transponder is from you, you could start start out with a low frequency, say 100 hz, and then you could increase the modulation frequency to improve your distance accuracy.

author
eismeraldo (author)ve6cmm2015-08-04

I'm very interested in
your ideas to increase the accuracy of the measurements.

Is it possible for you to
post a schema with some helpful comments?

author
eismeraldo (author)2015-08-04

I'm very interested in
your ideas to increase the accuracy of the measurements.

Is it possible for you to
post a schema with some helpful comments?

author
nipuna.sankalpa.566 (author)2015-07-05

please give me cct diagram i want it imediatly

author
pappihails (author)2015-05-14

Hi Guys, Great job and want to try this out myself.
Any chance on getting some more information from you?

author
naveenr5 (author)2015-05-05

Hi,
Nice work!!
Could you pls tell me how much is the estimate this

author
mz1371 (author)2015-04-20

Hi, very nice! If its possible send me a high quality schematic.

my E-mai: mojtabazare1371@yahoo.com

Thank you very much...

author
Neon_c (author)2015-04-20

Very nice! Thanks for including the algorithms and full schematic.The accuracy information is very useful. And your English writing is much better than my German distributors!

author
ve6cmm (author)2015-03-26

One other thing, the transmitter at the Interigating end is 434 MHz and the receiver is 868 MHz. These are dirty little transmitters and receivers and the likelyhood of the second harmonic of the transmitter affecting the sensitivity of the receiver is quite likely. You might want to try and find receiver and transmitter that are not on harmonically related! The transponder end is fine, as the second harmonic of the transmitter is much higher than the receiver frequency. There are ISM radios similar to what you are using that run at 303 MHz if I am not mistaken. Taking care of this problem could improve your effective range quite a bit and could stop false readings as the interigator receiver would not hear the interigator transmitter.

author
mobino (author)2011-03-24

Can you explain your example calculation in more detail?

How do you get 560ns from the displayed 17?

Also, how is a nanosecond timer achieved with 30Mhz?

A 10ns timer could be achieved with 100Mhz (10ns cycle time)

a 30Mhz cycle is aprox 33ns

never mind I answered my own question :)
17 * 33ns = 561ns

I like it

what does the circuit for the far side look like?

author
Jones Electronic (author)mobino2011-03-24

your self-answered question was right 17(displayed) * 33ns (from the 30MHz) = 561. so with the accuracy of this crystal we calculated with 560ns. this is acceptable at a resolution of ±5 meter, we dont care of one meter (1ns) more or less.
we described this as a timer which counts in nanoseconds, not in one nanosecond, sorry for this mistake!
we'll post some new photos from our new circuit and the second measure point soon, please feel free to contact us if you've got more questions

author

what is the 17 unit? is that in seconds?

author
carmaster (author)2011-03-30

Instead of using all those 74xx chips, why not use an Arduino?
Because it involves programming?

author
mobino (author)carmaster2011-04-01

I think because they need to be able to respond to a 30Mhz ripple.
Arduino couldn't - could it?

author
Jones Electronic (author)mobino2011-04-02

maybe they can, but we've got no experience with these "high-tech" chips.
they would be very helpful to backup the previous measurements so we can realize diagramms or such things. so maybe in the future we'll include one

author
mobino (author)Jones Electronic2011-04-04

The arduino clock is ~20Mhz. It could be used in place of the drivers to collect data and log it to a PC via serial. It could be used to perform a large number of measurements without manual work. With 3 different measurements you could do on-board trilateration and output 3D coordinates.

Getting an accurate count of millions or billions of ripples is not something any AVR can do by itself. You'd need a high quality TDC for reliable nanosecond accuracy of time of flight measurement.

This project is very good for long distance measurements but indoor positioning (as an example) would benefit more form pre-recorded data for comparison and multiple layers of averaging. I only mention this cause a lot of people would love to have something like this for rover/robot remote control. Unfortunately rf travels a bit too fast. for open field navigation timing ultrasound is a better option.

For me this is interesting for land surveying. I'd love to get this down to 30cm. If you could design a 1ns counter. I'd build it - with arduino logging for 3 bounces. :)

author
gocreeps1433 (author)mobino2015-03-25

Sir how can you build a 1ns counter in arduino?

author
PedroHenriqueGuida (author)2014-04-08

I'm Working on a very similar project using two arduinos with transmitters and receivers to measure their distance from one another. This post was a great help for the way I'll put the formulas in the algorithm inside programming.
For long distances though, atmospheric attenuation and dieletric materials contained along the waves path can change too much the final result.
I would advice a temperature e humidity component to adjust the calculations according to actual atmospheric conditions.
congratulations for your work !!

author

sir can you help me on this type of project?

author
ve6cmm (author)2014-05-07

Another way to do this would be to modulate the transmitted signal, and have that modulation at the far end modulate the 800MHz signal. You could then compare the phase difference of the transmitted signal with the one received, change the modulation frequency if needed to get better accuracy, and you would also eliminate the RX to TX time at the far end. All measurements could be made at audio frequencies, a scope could be used to compare the sent and returned waveform, and would allow you to see any interference in the signal. There are lot's of great ideas for this scheme here! Thanks for getting me thinking.........

author
gocreeps1433 (author)ve6cmm2015-03-25

sir can you help me about this topic?

author
ironstien (author)2014-07-11

can someone explain the use of all the schmitt triggers in the circuit ...

author
kurtzthegreat (author)2011-03-21

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

author
sierahotel (author)kurtzthegreat2014-04-18

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.