Re: Range-finding ultrasonic / infrared

From: Danny T (danny_at_nospam.oops)
Date: 01/04/05 

Date: Tue, 04 Jan 2005 07:31:56 +0000

Robert Monsen wrote:
> Danny T wrote:
>
>> What's the best (cheapest, quickest, easiest) way to detect obstacles
>> for a small robot? The book I have starts with infrared, and later
>> replaces them with ultrasonic. Infrared is way cheaper, but I don't
>> full understand how it works..
>>
>> I've got some phototransistors here, that seem to work exaclty like
>> LDRs, they just change the resistance with the light - except they
>> also work with infrared (as well as normal light). I've seen infrared
>> LEDs, and infrared phototransistors - am I right in thinking these are
>> simple filtered to only detect IR, instead of normal light?
>>
>> Would these be accurate enough to be able to get a range, or would it
>> simple be a yes/no if something's there? Ideally, I want to be able to
>> detect a) if there's anything within, say, 6 inches, and also if
>> there's anything within, say, 3 inches. That way, as things get near,
>> I'll start turning my robot, but if it doesn't turn quick enough,
>> it'll increase the turn when it gets closer.
>>
>> Thanks,
>
>
> You can buy units that are designed as IR distance sensors. They give
> you either a voltage (which you can read with the comparator or a/d) or
> a binary output. The Sharp GP2D120 comes to mind. Here is a datasheet:
>
> http://www.technologicalarts.com/myfiles/data/gp2d120.pdf
>
> You can get them at the various robotics webstores. However, they are
> cheaper at Arrow electronics. Make sure you get some JST connectors,
> because they are a bit difficult to run without them. Acroname sells
> them with the connectors and wires for $12.50 plus shipping:
>
> http://www.acroname.com/robotics/parts/R146-GP2D120.html
>
> I've built robots with these before, and they work pretty well. One
> issue they have is that they are *really* directional. This is an issue
> when you are trying to detect obstacles, and mounting becomes critical.
> That is one thing to say for ultrasonics.

Sounds good, but Acroname don't have visible shipping costs for the UK!
Cheapest I've found here is:
http://www.active-robots.com/products/accessories/sensors.shtml

But I'll have a look around. I'll probably need 2 or 3, but looks like
they'll do the job! :)

> You can also just use a bump sensor, like the roomba.
>
> http://www.irobot.com/home.cfm

There's something more elegant about a robot that moves around without
hitting things... Imagine seeing people walking around an office by
bumping off walls ;-) 

-- 
Danny

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