Laser Rangefinder

[kbhattac]

Hi,

I'm trying to create an autonomous robot (on NXT platform of course) and for that I need to create accurate maps of the surroundings. I've read quite a bit on different types of sensors, their accuracy, linear response etc, and came to the conclusion that a Laser rangefinder would be ideal for my case. (0.05m to 10m range, with 1cm accuracy, tolerant to significant clutter).

The idea is to build a Laser range finder based either on the triangulation concept (like the Revo LDS) or phase shifter concept (e.g. used in the BOSCH DLE-40). The other option based on the TOF calculation is way beyond my budget (like the SICK or Hokuyo sensors), and this out of consideration.

Now the question to this forum is what is the best way to interface the output of the sensor to the NXT MCU? I'm using RobotC.
1) Should I (or could I) channel the raw analog data directly to the NXT for processing?
2) Or should I convert the raw sensor data using a DSP (like the Piccolo TI TMF320F28xx series MCU), and channel it to the NXT digitally?

Kind regards,
Kaushik.

[mattallen37]

Can you direct us to the specific sensor you are considering?

Just a little info about the NXT analog input: It uses a 10-bit ADC with ground and sensor supply (4.3-4.7v) as reference. It also has a built-in 10k resistor pulling the line to sensor supply.

I would probably recommend using using an additional uC for signal processing, but it somewhat depends on the sensor.

[kbhattac]

Thanks for the prompt response. I'm making a sensor myself so I've all the flexibility to tailor it. I've not bought anything yet, so all options are open.

[aswin0]

I would consider to make a triangulation based device from a NXT camera from mindsensors and a custom build laser. Or you could use the laser that Ray McNamara sells. You can run this from the NXT.
Phase scanning lasers are expensive and hard to pair with the NXT.

[mattallen37]

In that case, I would almost definitely use a uC for processing control of modes, linearization etc.

[kbhattac]

In that case, I would almost definitely use a uC for processing control of modes, linearization etc.

@aswin0
That gadget is more of an obstacle detector than a range finder.

But I did not get why interfacing with a phase shift laser range finder could be difficult? The NXT has a 10 bit ADC for digitizing the phase detector output? I found this article very interesting: http://www.element14.com/community/docs ... r-solution

And they are not that expensive after all. You get sub $100 hand held devices like the Bosch DLE-40 employing phase shift laser range finders.

@mattallen37
Could you please elaborate on your statement?

[mattallen37]

Well, with a uC, you could have the option to enable/disable the laser, linearize the readings before the NXT gets them, etc. There is so much a uC could do when interfacing the NXT to electronics. I really haven't studied any laser measurement technology, so I'm not really sure what all the uC could be used for. I just know that whenever I interface the NXT with my own circuits, using a uC often opens up many doors of possibilities.

[kbhattac]

That's correct. But I'm wondering why can't I do that stuff with the NXT uC itself?

[mattallen37]

You probably could, but NXT resources can be very expensive. Each sensor port only has 2 GPIOs, plus the ADC IO. Many uCs have at least 16-20 IOs, and you can run as much math as you want, without slowing down the NXT VM.

If all you need is an ADC, then the NXT line should work fine, but you might need an OP amp with a gain of 1 because of the 10k pullup on the NXT ADC.

Edit: I would personally use a uC, even if I could connect it directly to the NXT.

[aswin0]

@aswin0
That gadget is more of an obstacle detector than a range finder.

What is the difference?

But I did not get why interfacing with a phase shift laser range finder could be difficult? The NXT has a 10 bit ADC for digitizing the phase detector output? I found this article very interesting: http://www.element14.com/community/docs ... r-solution

And they are not that expensive after all. You get sub $100 hand held devices like the Bosch DLE-40 employing phase shift laser range finders.

I do not know of any succesful hobby implementations of this. I do know of serious attempts to try to hack commercial range finders. The NXT certainly can't do it.