micro second

how do I take time in the order of microsecond from cpu?thanx

[Walter Roberson]

This question is still open, and the content of it still applies. Please do not create new questions for the same purpose.

Answer 1

[Walter Roberson]

This requires OS specific methods that might be hardware-specific as well.

For Windows, here is an ActiveX control .

I emphasize again that is likely that the times you obtain this way will be worthless to you, as you have no control over the OS scheduler or the amount of time that MATLAB will take to make the call. MATLAB could, for example, decided at random that it was time to do memory management, or time to service a different interrupt, both of which will take unknown amounts of time.

If you need a timer with higher resolution than 1 kHz, then you should be using a real-time system with hardware that supports such timers.

Remember too that with microsecond measurements, you are measuring in multiples of 300 metres of travel path; if my tired brain has it right, that would mean having to do the equivalent of an fft on 6 billion readings in order to resolve down to 1 m/s velocity.

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It is my belief that the project you very briefly outlined a couple of months ago requires purpose-built hardware to accomplish -- possibly even a custom chip design. Possibly you should be switching over to modeling in Simulink using an HDL simulator for eventual burning in to a chip.

Answer 2

[Paskah Nainggolan]

so it's impossible to do?

[Walter Roberson]

You will have to be more specific about what your goals are, including your performance criteria. And you will have to be specific about how you intend to measure the distances, as you do not appear to be using a RADAR-like time-to-return measurement.

[Paskah Nainggolan]

in a project that I do. I use radio waves to detect the distance of objects.to detect the distance I use the delay time value.

Can you tell me how do I access time untill microsecond?thanx

[Walter Roberson]

Remind me of the radio frequency you are using for this? And the minimum and maximum distance range you need the device to work with? And of the distance resolution that you need to be able to achieve?

1 microsecond corresponds to 1 MHz, which is just short of 300 meter wavelength. 1 MHz is 1000 kHz, which is right in the middle of the commercial AM band. AM is a licensed band, but depending on the regulations for your country, you might be able to transmit unlicensed if you use sufficiently low power (e.g., 10 milliwatt ERP). As, though, you would likely be contending with a local AM station at that frequency, or with roll-off from AM stations with nearby frequencies, you are going to have to use distinctive signal chirps to differentiate between the commercial transmissions and your radar transmissions. The chirp detection and filtering out from other signals would either have to be done in hardware or else you would have to go for a higher time resolution (probably at least 8 times as high) -- or else you will need to take that in to account in the 1 microsecond time resolution, sampling a lower frequency signal at that rate. For example, you might be able to use LowFER, http://en.wikipedia.org/wiki/LowFER and sampling about 6 times per pulse. If you do use such low frequencies, though, you might require an antenna about 100 meters tall; you might also be contending with some established stations as the groundwave effect makes these stations receivable for over 1000 km. http://en.wikipedia.org/wiki/Long_wave

Answer 3

[Paskah Nainggolan]

i nedd the code mr, can you help me mr walter?

[Walter Roberson]

I cannot program or guide when I do not have fundamental information about the goals and the available equipment.

You need to write up a project specification -- a detailed description of the functionality to be provided by the code, and of any real-time constraints, and of which software tools must be used or must not be used, and of the hardware that will be used, including the required accuracy and speed of the hardware and including any hardware interface requirements. If you don't know of any hardware that can meet the requirements, then it is your responsibility to do research to find at least one (available!) piece of hardware that has been tested and found to be able to handle those requirements in practice (not just on the datasheets).

And once you've written the detailed project specifications, you need to go back and re-read them all and make sure everything fits together properly. Imagine that you are submitting the project specifications out to contract bid, and imagine that it is standard practice in the industry to charge a minimum of $5000 extra per change to the specification -- imagine that getting the specification wrong in any way is *expensive*, so it has to be done thoroughly the first time.

If you are hoping someone else can provide code, you need to be very specific about what you need the code to do.