Need advice about sensors for collision avoidance outdoors.

[keith1200rs]

It depends how you measure phase, but the system I designed was not ambiguous until 360 degrees. Some phase shift measuring systems may not be able to discriminate between 170 degrees and 190 degrees though.

Keith.

 

[Hewhowalk]

Re: Need advice about sensors for collision avoidance outdoo

When I read about it, it seems like when you mix two measured phases you get an expression that is a cosine of the phase-shift instead of the actual phase-shift, which makes as you mentioned only the first 180 degrees unambigous.

So how did you system differ from this? Was it different mixing circuit giving other equiations or was it a compleatly different approach?

 

[keith1200rs]

Ah, I see the confusion. The method you are talking about mixes the incoming signal with the returned signal so you get double the frequency and a DC component which is the cosine of the phase difefrence. I did consider that but it has some problems, as you probably know.

The the technique I used mixes the returned signal with a slightly different frequency. So, you might modulate with 10MHz and mix with 10.01MHz giving a 10kHz difference. The phase of that beat is the same as the phase difference of the 10MHz signals. So, a bit of zero crossing detection and an FPGA and you can measure the phase difference. It works for 360 degrees.

Keith.

Added after 10 minutes:

By the way, that's why I referred to it as a heterodyne system rather than "phase shift". I have more recently done true phase shift systems with the AD8302.

Keith.

 

[Hewhowalk]

Do you know any commercially available systems that use this technique? And it has to be something that I can interface with a microprocessor. The only "phaseshifting" equipment I have found so far is handheld measurement-devices and they can't be used that way.

 

[keith1200rs]

The problem is that there isn't a lot of commercial stuff out there and it is designed for specific applications so may not be suitable for your needs. If you can find one, the closest to your application would be vehicle collision avoidance which is now available on a few cars (Volvo and Mercedes are two I know of) although the maximum range will be longer than you need. I don't know if it is common enough to be a module you can just buy. More likely it has been developed by someone like Bosch specifically for each manufacturer. It might be an avenue worth investigating though.

People like Sharp, TDK, Murata, Sony Semiconductor, Toko, Mitsubishi may have sub assemblies or "building blocks" but I am only guessing.

Keith.