Distance measurement sensor..

[adiee250988]

I would like to build laser distance measurer using FPGA as the controller. but i dont know where to find the suitable sensor that can connect with the FPGA.
I would like to find a sensor that can measure around 5-10m (its already enough for me) because the point is i want to connect with the FPGA..
i want to buy the IR transmitter and receiver for a try, but i dont know how the receiver work.. which mean where i want to put the receiver?
somebody plz help me.. correct me if im wrong.

[yonghui]

hi,

the FPGA detecting digital input?

[adiee250988]

i think so.. because all the coding using the VHDL or verilog coding and it playing with bit.. but i think, the FPGA also can detect the analog, just depend how we code it..

Can i ask u something, how far the IR can reach which mean the distance where the receiver can detect accurately..

im planning to build IR transmitter and receiver so that the IR transmit that bounce can be detect by the receiver and give signal to FPGA.

[ober]

1. This is very great project, but using laser.... might be very difficult to get a laser and you might need to do some more research on the controlling part.

2. IR, can actually go a few meters, but require special modulation, and of course require filter at receiver to ensure the signal received is from the correct IR source which is the modulated IR transmitter. Never try to modulate IR transmitter yet, so I can only advise to search from google. Still, I would say it is not suitable for 5 to 10 meter range, and not suitable for radius scanning.

[adiee250988]

If im using Laser, the clock must be set to 300Mhz but the problem is that the FPGA only have 50Mhz clock. From my lecturer advice, there are some coding to increase the clock. So before i take the larger risk by thinking about the coding, so better i replace the laser with IR. that just for the testing part. because the IR need less voltage input than the laser.

i think for better efficiency input from IR transmitter, i want to build one IR Transmitter with 2 or 3 IR receiver so that the triangulation of the IR beam can get make the IR receive it precisely. what do u think?

[lordtct]

Judging from your very short measurement distance, TOF laser rangefinding is not a wise idea for two reasons:

1. Your circuit must be able to shoot pulsed laser beams at a rate of at least 1/10th of your minimum time of flight. It takes only 66 ns for round trip at 10 m. At 5 m, you're looking at 33 ns. So yes, your lecturer is right: Your timing circuits needs to be clocked at a whooping 300 MHz. But the actual problem is not the FPGA, but rather HOW you are going to design a power circuit to fire such extremely accurate and fast pulses with near zero margin for timing errors.

2. The million dollar question: If you are able to shoot 300 MHz pulses, what are you going to use to sense the returning pulse? I don't think you can find any affordable photodetectors for the job! That's your final nail in the laser coffin.

On infrared distance measurement, I'm afraid it will not be very straightforward. If you calibrate distance according to IR receiver intensity, you're going to get in trouble because not all objects have the same specularity or reflectivity. If you calibrate the sensors w.r.t. a black object, don't expect the sensor to work for say, a piece of paper.

In the manufacturing industry, we do have something called a "displacement meter" for extremely accurate liquid level measurement. It works by shooting a powerful N-IR laser beam at the moving surface and the beam gets reflected to a 1 dimensional array of photodetectors. Changing heights of the measurant will cause the beam to fall at different positions on the 1D detector. There is of course, the need to calibrate the meter for different height ranges by varying the focusing lenses' powers and the position of detector itself.

If you want to try this yourself, you could aim an infrared laser at an object and measure the response from a 1D photodetector, say, Hamamatsu S3932 (with visible light filter). Knowing all your reference points, you could apply simple trigonometry to obtain the distance. You may need a concave lens to focus the beam in case it doesnt fall on the detector's edges.

Hope that helped!

[adiee250988]

ur information is very helpful to me.. that is why the problem for me is to buy the laser sensor. i will try with that idea first. just to test the experimental project did work. especially to integrate the coding with the sensor.. but i think by put the concave lens in front of the IR really smart idea.. i will try with that first. thank u so much

[happyrush]

Hi there,

You are not able to get this laser range finder done unless you are expert in PLL.

Only PLL can pull up the frequency. The photodiode sensor must be avalanche photodiode with wavelength 600nm to 750 nm ,very expensive.

your shoot out signal + carrier signal must be able to change the timming due to far or near distance.

to get the distance, you are not going to use TOF(time of flight), but you can use phase difference between shooting waveform and receiving waveform.

Even laser, you need the optical knowledge.It need a lens to focus the receiving signal,the structure is highly complicated(base on bosch laser range finder)

This project long time done by BOSCH ,LEICA, FLUKE,PRECASTER, you can buy the device.

[adiee250988]

yeah,, that is why i have problem in designing the laser.. furthermore, the laser equipment is really expensive..
Lordtct post can be classified as cheaper distance measurement method by using infrared sensor.. but the maximum distance for the infrared sensor that i had search is so short in distance.. that is why by using the concave lens can make the infrared beam travel farther.. i hope so..

i just need to build the sensor part.. the clock can be done by using vhdl coding using FPGA controller.. maybe there are coding that can multiply 50Mhz clock to 300Mhz clock.. im still searching for it..

[happyrush]

Hi,

I am familiar with altera FPGA, there is no coding can multiply the frequency, it only can happen in hardware, never in coding, coding only can do clock divider.

You are not to be keep your idea only on FPGA, you still using FPGA but you also can add in a 300MHZ oscillator(http://my.farnell.com/fox/fxo-lc735r-21 ... dp/1538957),FPGA only generate an unique signal to mix with your carrier.

But i wonder IR can support such a high frequency, normally IR run on KHz.Hehe...Good luck!