SparkFun Forums 

Where electronics enthusiasts find answers.

Have questions about a SparkFun product or board? This is the place to be.
By schizoghost
I had this idea yesterday while I was trying to find a way to recreate the principle of a Gps but on a much smaller scale.

Basicaly, the idea would be that you have an emitter and a receiver.

Both components has a really precise clock that would be synchronized.

From this point the emitter would send the time that he emits in an encrypted ultrasound.
This ultrasound would be decrypted by the receiver and would compare the lag between the actual time and the emitted sound.

Because sound travels at a speed of around 320 m/s, I could get the distance between the two objects.

tell me what you guys think
I know there is many factor to consider.
And I post this idea as I think that this idea as to be brainstormed by smart people (which I am not)

although I think its an awesome idea to work on

By riden
I've seen something like this done in the past only for location by triangulation. The technique used a combination of IR and ultrasonic sensing. There are a number of issues, but you could put something together easily enough to try. Basically, the receiver needs to have a high precision timer, not a RTC (real-time clock) per se as that would require syncing both RTCs.

The transmitter sends out a strobe of infrared light (IR) followed by an ultrasonic burst. The IR strobe is picked up by the receiver causing the receiver to start its timer and listen for the ultrasonic pulse. When the ultrasonic pulse is received, the receiver turns off the timer and calculates the distance. This works pretty well because the speed of light is so much faster than the speed of sound.

You do need line-of-sight or IR repeaters for this to work and it can be difficult to detect the ultrasonic burst after a certain distance. Read angelsix's excellent thread about his ultrasonic project. Keep in mind that the speed of sound varies with temperature.
By esklar81
riden wrote: Keep in mind that the speed of sound varies with temperature.
and humidity and pressure (and, therefore, altitude). The apparent speed of sound also varies with windspeed. :(

For the record, what was originally proposed here does not implement the fundamental method of GPS. GPS does not rely on absolute time of propagation from a satellite to the receiver, it relies on the differences in times of propagation from several satellites to a receiver. That way, there's no need for the receiver to know the absolute time.

The proposed method more closely resembles SONAR, where distance is measured by timing the period between when a pulse is transmitted and when its echo is received. The major difference is that the proposed system puts the transmitter and receiver on different objects, doubling the range of which it could work, but imposing a much more stringent timing requirement (synchronized absolute time clocks vs a short-duration event timer).
By schizoghost
Tell me if I am wrong but low frequency waves travels better without any alteration of the frequency than ultrasound. On the other hand, there would be way much more exterior sources of noise than ultrasound.

I thought of another idea.

Have you guys ever heard of a theremin?

basically, a theremin emmits a really high electromagnetic waves in the air and takes the feedback of this wave and substract it from the initial wave. In this way, you get the shift between the first wave and the feedback. Because the shift is really small, it is possible to tune the theremin in a way that the substraction gives a audible frequency in form of a sound.

Would it be possible to get two crystals that are first synchronized to use this principle to evalute the distance from two objects.

(I dont have any knowledge, I m just brainstorming)

also, what would be the frequencies that travels the best without alteration of the sound?