Sensors

Discussions around autonomous, semi-automatic and intelligent robots and systems.

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BeligerAnt
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Sensors

Postby BeligerAnt » Thu Nov 17, 2005 8:41 pm

With reference to Adam's question about sensors in the Antweight thread, thought I'd kick something off here.

There are two main ways of doing opponent sensing: ultrasonic and infra-red (IR). Both work on the principle of reflection, ultrasonic uses sound, IR uses light.

For my minisumo robot I am going to try IR. To avoid problems with ambient light I am using IR modulated at 38kHz with a synchronous detector which can effectively filter out ambient light and other infra-red. This all comes in one handy IC, the IS471F from Sharp. It's available from Farnell and several online robotics suppliers. Just add an IR LED, resistor and capacitor.

This gives a "yes/no" detection of an opponent within range. It doesn't give any indication of range.

For an analog IR range-finder, the Sharp GP2 series are popular, but more expensive than the IS471F. Farnell stock several, including stock code 9707859 which gives an analog output over the range 4-30cm. Other ranges are available.

The IS471F soultion costs about ?2.50, whereas the GP2 devices are nearer ?10. Of course, you need (at least) two sensors to detect front/left and front/right to find your target.

I haven't looked at ultrasonic methods in detail, but basically it works like radar - send out a "ping" and wait for the echo to come back. Distance is then proportional to time.
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Lincoln
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Scanning IR Range sensor

Postby Lincoln » Thu Nov 17, 2005 10:41 pm

I've seen several designs that advocate the use of one of the Sharp GP2 IR range sensors mounted on a servo horn so that you can scan it from side to side rather than having to have multiple sensors.

It sounds like we've been thinking along the same lines as I've had some of both types of sensor sitting around waiting to get some attention for a few months now.

You can get a kit to make a complete sensor with a pair of IR LEDs and a small PCB from www.robotmaker.co.uk in the form of their "ProxDots".

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BeligerAnt
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Postby BeligerAnt » Wed Nov 30, 2005 8:18 pm

I got my IS471F sensors from Farnell with a note saying they would not be stocking them any more. :(

Some digging around revealed that they are now stocking the IS471FE (lead free version) instead. :)

This is happening more and more with Farnell. They seem to be changing all their stock numbers as they change over to lead-free parts, even if the manufacturer's part number is not changing! If you find a part listed as "no longer stocked" or even "no longer manufactured" check for an "alternatives" link. Usually it's exactly the same part, but in a lead-free package.
Gary, Team BeligerAnt

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peterwaller
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Postby peterwaller » Tue Feb 28, 2006 2:09 pm

I have just got some SY-CR102 from Maplin. These are a tiny package containing an infared sender and receiver aparently for optical encoders but I think they will be ideal for detecting the white line at the edge of the arena. I will let you know how good they are when I try them out. I got the new ATMega168 processor going last night in the programmer board. Apart from using a different include file and configuring a different port for the PWM output my speed controller code for the Tiny13 processors worked without change. I need to move the processor onto a some veroboard for the the prototype and get the programmer talking to that and then I can start looking at writing some code. I thought I would get the edge sensors working first and see if I can get it running around the arena just avoiding falling off. Must go out and buy some MDF for the arena so I can test it out.

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Postby peterwaller » Wed Mar 01, 2006 9:36 pm

The SY-CR102 works well. At a height of 5 mm they give a full 6.5v swing between the black and the white surface. I have now also built and painted the sumo arena.

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BeligerAnt
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Postby BeligerAnt » Wed Mar 01, 2006 10:28 pm

peterwaller wrote:(28 Feb) Must go out and buy some MDF for the arena so I can test it out ... (1 Mar) I have now also built and painted the sumo arena.

Oh what it is to be retired eh? :wink:
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Remote-Controlled Dave
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Postby Remote-Controlled Dave » Wed Mar 01, 2006 10:36 pm

Diary of a Rambling Retired Roboteer
Die Gracefully Robotics
Winner - AWS 39


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