# 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.
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ve6cmm28 days ago

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.

ve6cmm5 months ago

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.

28 days ago

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

Is it possible for you to

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

Is it possible for you to

please give me cct diagram i want it imediatly
pappihails3 months ago

Hi Guys, Great job and want to try this out myself.

naveenr53 months ago

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

mz13714 months ago

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

my E-mai: mojtabazare1371@yahoo.com

Thank you very much...

gvillenap1 year ago

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

Jones Electronic (author)  gvillenap4 months ago

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

10 months ago

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

5 months ago
Nope, i didnt. I did another project, but Im still interisted in this one
Neon_c4 months ago

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!

ve6cmm5 months ago

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.

mobino4 years ago
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?
Jones Electronic (author)  mobino4 years ago
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
5 months ago

what is the 17 unit? is that in seconds?

carmaster4 years ago
Instead of using all those 74xx chips, why not use an Arduino?
Because it involves programming?
4 years ago
I think because they need to be able to respond to a 30Mhz ripple.
Arduino couldn't - could it?
Jones Electronic (author)  mobino4 years ago
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
4 years ago
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. :)
5 months ago

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

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.

5 months ago

sir can you help me on this type of project?

ve6cmm1 year ago

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.........

5 months ago

ironstien1 year ago

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

kurtzthegreat4 years ago
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
1 year ago

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.

Jones Electronic (author)  kurtzthegreat4 years ago
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.
4 years ago
@Jones Electronics: dude can u just mail me a schematic with better quality and visibility to this e-mail address "pendyala87@gamil.com"
Jones Electronic (author)  AvinashPendyala4 years ago
here's the best schematic

http://www.instructables.com/files/orig/F3V/KH3R/GLFUDO8C/F3VKH3RGLFUDO8C.jpg
4 years ago
thanks a lot bro.....I owe you one
Reiff1 year ago
Okay, obviously not for me, to complicated. I was looking for some way to find another persons (on a 2-way hand-held radio) approximate location. I always wondered if there is a simple way to find out where there direction is, or how far the other person is from my radio. Maybe there isn't a way, because I know tech people always like to say to dummy's "It's not magic" (isn't that right!).
1 year ago

They call it Fox Hunting, but it's not a digital computerized method you might see on csi, Fox Hunters use directional yagi antennas and goal post-like dipoles and rotate the device to find the null points of the signal in attempts to figure out what direction it's coming from. Apparently it is not easy to learn and takes a lot of practice.

TheArsonator1 year ago

Could this device send a signal through an engine block?

1 year ago

No, you can't measure through an engine block using radio waves. If you've ever tried to get a gps fix in an area of tall buildings, you've seen the position jump wildly around, because a radio wave will eventually reach every point in space, but often takes a "long path" to get there. The longer flight time throws off the accuracy of measurements. Also, if the engine block is grounded, or acting as a ground, the radio waves will stop there and flow to earth, instead of passing through and continuing on to you're receiver.

Jones Electronic (author)  TheArsonator1 year ago

Of course it can! But i think it will weak the signal so it maybe not be able to transmit it more than 50 meters

1 year ago
Sweet. Does that affect the accuracy?
SirThaiSNU2 years ago
Thank for sharing Jones.
It is nice project. Can you upload the schematic at the second point? How can you connect RX433MHz and TX866MHz? Thank you.
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