Subject:
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Another DIY sensor
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 16 Nov 2000 17:45:27 GMT
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Original-From:
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John Barnes <barnes@sensors^AvoidSpam^.com>
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Viewed:
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685 times
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My continuing journey into the world of DIY RCX sensors
has lead me to a home made rotation sensor which may be
of interest.
Since the RCX light sensor reports values in the range 0 - 100
and my compass sensors are thus constrained to report 0 - 360
as a scaled value in the range 0 - 100, I have settled on a new
scheme in which there are 100 RCX degrees in a circle. Actually
not a bad system of measurement when you get used to it.
Needing to rotate detection sensors with a matching resolution, I
initially used the standard Lego rotation sensor, but it needs
considerable gearing to get up to 100 counts per rev. and suffers
the inevitable backlash problems. So I decided to investigate DIY
rotation sensors. The first two or three simply didn't work. Then
I hit upon the magic recipe;
I made a slotted disk using overhead transparency material in the
laser printer. A simpe disk with 25 black segments.
Then I found that digikey sell an Omron dual optical interrupter
module.
The transparent disk is glued on a piece of modified Lego which
fits a cross axle. (I used a small propellor with the blades carefully
removed). I built the thing up sandwiched between a couple of
technic style plates with an RCX interface consisting of the usual
6 diode and capacitor interface. The two outputs from the interrupter
go through a LM393 dual comparator and are summed with 6.8k
and 15k resistors to the RCX giving almost exactly the same
voltages as I measured from a real rotation sensor.
The 25 black slots give the required 100 counts per rev! It works
great.
If anyone needs any more detail, please let me know. I will try to
take a few pics this weekend.
JB
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Message has 3 Replies:
 | | Re: Another DIY sensor
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| (...) Use RAW mode. Then you get 2500 to 0 (I think it was) Dean -- Coin-Op's For Sale!: (URL) Lego Workshop: (URL) Lego Club: (URL) (24 years ago, 16-Nov-00, to lugnet.robotics)
| | | Re: Another DIY sensor
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| (...) Then: (...) Now you tell me!!!! Just after I finished implementing a set of cheap and cheerful nqc fixed point transcendental functions based on 100 RCX degrees per rev! JB (24 years ago, 16-Nov-00, to lugnet.robotics)
| | | Re: Another DIY sensor
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| Does the ratio of the disk track diameter and the seperation between the interuptors allow you get 90 degrees (optical) seperation ? IE could you get quadrature off of it ? BTW, Please post pictures : ) Thanks, -JSM (24 years ago, 17-Nov-00, to lugnet.robotics)
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